arXiv daily: High Energy Astrophysical Phenomena (astro-ph.HE)

Authors:Anjasha Gangopadhyay, Keiichi Maeda, Avinash Singh, Nayana A. J., Tatsuya Nakaoka, Koji S Kawabata, Kenta Taguchi, Mridweeka Singh, Poonam Chandra, Stuart D Ryder, Raya Dastidar, Masayuki Yamanaka, Miho Kawabata, Rami Z. E. Alsaberi, Naveen Dukiya, Rishabh Singh Teja, Bhavya Ailawadhi, Anirban Dutta, D. K. Sahu, Takashi J Moriya, Kuntal Misra, Masaomi Tanaka, Roger Chevalier, Nozomu Tominaga, Kohki Uno, Ryo Imazawa, Taisei Hamada, Tomoya Hori, Keisuke Isoga

Abstract: We present optical, near-infrared, and radio observations of supernova (SN) SN~IIb 2022crv. We show that it retained a very thin H envelope and transitioned from a SN~IIb to a SN~Ib; prominent H$\alpha$ seen in the pre-maximum phase diminishes toward the post-maximum phase, while He {\sc i} lines show increasing strength. \texttt{SYNAPPS} modeling of the early spectra of SN~2022crv suggests that the absorption feature at 6200\,\AA\ is explained by a substantial contribution of H$\alpha$ together with Si {\sc ii}, as is also supported by the velocity evolution of H$\alpha$. The light-curve evolution is consistent with the canonical stripped-envelope supernova subclass but among the slowest. The light curve lacks the initial cooling phase and shows a bright main peak (peak M$_{V}$=$-$17.82$\pm$0.17 mag), mostly driven by radioactive decay of $\rm^{56}$Ni. The light-curve analysis suggests a thin outer H envelope ($M_{\rm env} \sim$0.05 M$_{\odot}$) and a compact progenitor (R$_{\rm env}$ $\sim$3 R$_{\odot}$). An interaction-powered synchrotron self-absorption (SSA) model can reproduce the radio light curves with a mean shock velocity of 0.1c. The mass-loss rate is estimated to be in the range of (1.9$-$2.8) $\times$ 10$^{-5}$ M$_{\odot}$ yr$^{-1}$ for an assumed wind velocity of 1000 km s$^{-1}$, which is on the high end in comparison with other compact SNe~IIb/Ib. SN~2022crv fills a previously unoccupied parameter space of a very compact progenitor, representing a beautiful continuity between the compact and extended progenitor scenario of SNe~IIb/Ib.

Authors:Jakob Böttcher for the IceCube Collaboration

Abstract: For about a decade the IceCube Neutrino Observatory has been observing a high-energy diffuse astrophysical neutrino flux. At these energies, an important source of background are the prompt atmospheric neutrinos produced in decays of charmed mesons that are part of cosmic-ray-induced air showers. The production yield of charmed mesons in the very forward phase space of hadronic interactions, and thus the flux of prompt neutrinos, is not well known and has not yet been observed by IceCube. A measurement of the flux of prompt neutrinos will improve the modeling of hadronic interactions in cosmic-ray induced air showers at high energies. Additionally, in the context of astrophysical neutrino measurements, understanding this background flux will improve the measurement precision of the spectral shape in the future. In particular, the analysis of up-going muon neutrino-induced tracks in IceCube provides a large sample of atmospheric neutrinos which likely includes prompt neutrinos. However, the measurement of a subdominant prompt neutrino flux strongly depends on the hypothesis for the dominant astrophysical neutrino flux. This makes the estimation of upper limits on the prompt neutrino flux challenging. We discuss the extent of this model dependency on the astrophysical flux and propose a method to calculate robust upper limits. Furthermore, a possible dedicated search of the prompt neutrino flux using multiple IceCube detection channels is outlined.

Authors:P. Gitika, M. Bailes, R. M. Shannon, D. J. Reardon, A. D. Cameron, M. Shamohammadi, M. T. Miles, C. M. L. Flynn, A. Corongiu, M. Kramer

Abstract: We present a flux density study of 89 millisecond pulsars (MSPs) regularly monitored as part of the MeerKAT Pulsar Timing Array (MPTA) using the L-Band receiver with an approximately two week cadence between 2019-2022. For each pulsar, we have determined the mean flux densities at each epoch in eight $\sim$97 MHz sub-bands ranging from 944 to 1625 MHz. From these we have derived their modulation indices, their average and peak-to-median flux densities in each sub-band, as well as their mean spectral indices across the entire frequency range. We find that the vast majority of the MSPs have spectra that are well described by a simple power law, with a mean spectral index of -1.86(6). Using the temporal variation of the flux densities we measured the structure functions and determined the refractive scintillation timescale for seven. The structure functions provide strong evidence that the intrinsic radio luminosities of MSPs are stable. As a population, the average modulation index at 20 cm wavelengths peaks near unity at dispersion measures (DMs) of $\sim$20 pc cm$^{-3}$ and by a DM of 100 pc cm$^{-3}$ are closer to 0.2, due to refractive scintillation. We find that timing arrays can improve their observing efficiency by reacting to scintillation maxima, and that 20 cm FRB surveys should prioritise highly scintillating mid-latitude regions of the Galactic sky where they will find $\sim$30% more events and bursts at greater distances.

Authors:L. Ducci, C. Malacaria

Abstract: X-ray spectroscopy is a powerful technique for the analysis of the energy distribution of X-rays from astrophysical sources. It allows for the study of the properties, composition, and physical processes taking place at the site of emission. X-ray spectral analysis methods are diverse, as they often need to be tailored to the specific type of instrument used to collect the data. In addition, these methods advance together with the improvement of the technology of the telescopes and detectors. Here, we present a compact overview of the common procedures currently employed in this field. We describe the fundamental data structure and the essential auxiliary information required for conducting spectral analysis and we explore some of the most relevant aspects related to statistical and computational challenges in X-ray spectroscopy. Furthermore, we outline some practical scenarios in the context of data reduction, modeling and fitting of spectra, and spectral simulations.

Authors:Xinxin Wang, Ye-Zhao Yu

Abstract: Fast radio bursts are a class of transient radio sources that are thought to originate from extragalactic sources since their dispersion measure greatly exceeds the highest dispersion measure that the Milky Way interstellar medium can provide. Host Galaxies of twenty-two fast radio bursts have already been identified. In this paper, the dispersion measurement of these fast radio bursts produced by the Milky Way interstellar medium, and the intergalactic medium is obtained through known physical models to yield the host galaxy dispersion measure. It is observed that the host galaxy dispersion measure increases with its redshift value. We also obtained that the host galaxy dispersion measure has different distribution between repeaters and non-repeaters. It is noted that the reason for the divergence of the host galaxy dispersion measures should be accounted for by the difference in their local environment.

Authors:K. Ertini, G. Folatelli, L. Martinez, M. C. Bersten, J. P. Anderson, C. Ashall, E. Baron, S. Bose, P. J. Brown, C. Burns, J. M. DerKacy, L. Ferrari, L. Galbany, E. Hsiao, S. Kumar, J. Lu, P. Mazzali, N. Morrell, M. Orellana, P. J. Pessi, M. M. Phillips, A. L. Piro, A. Polin, M. Shahbandeh, B. J. Shappee, M. Stritzinger, N. B. Suntzeff, M. Tucker, N. Elias-Rosa, H. Kuncarayakti, C. P. Gutiérrez, A. Kozyreva, T. E. Müller-Bravo, T. -W. Chen, J. T. Hinkle, A. V. Payne, P. Székely, T. Szalai, B. Barna, R. Könyves-Tóth, D. Bánhidi, I. B. Bíró, I. Csányi, L. Kriskovits, A. Pál, Zs. Szabó, R. Szakáts, K. Vida, J. Vinkó, M. Gromadzki, L. Harvey, M. Nicholl, E. Paraskeva, D. R. Young, B. Englert

Abstract: We present extensive ultraviolet (UV) and optical photometric and optical spectroscopic follow-up of supernova (SN)~2021gno by the "Precision Observations of Infant Supernova Explosions" (POISE) project, starting less than two days after the explosion. Given its intermediate luminosity, fast photometric evolution, and quick transition to the nebular phase with spectra dominated by [Ca~II] lines, SN~2021gno belongs to the small family of Calcium-rich transients. Moreover, it shows double-peaked light curves, a phenomenon shared with only four other Calcium-rich events. The projected distance from the center of the host galaxy is not as large as other objects in this family. The initial optical light-curve peaks coincide with a very quick decline of the UV flux, indicating a fast initial cooling phase. Through hydrodynamical modelling of the bolometric light curve and line velocity evolution, we found that the observations are compatible with the explosion of a highly-stripped massive star with an ejecta mass of $0.8\,M_\odot$ and a $^{56}$Ni mass of $0.024~M_{\odot}$. The initial cooling phase (first light curve peak) is explained by the presence of an extended circumstellar material comprising $\sim$$10^{-2}\,M_{\odot}$ with an extension of $1100\,R_{\odot}$. We discuss if hydrogen features are present in both maximum-light and nebular spectra, and its implications in terms of the proposed progenitor scenarios for Calcium-rich transients.

Authors:Noam Soker Technion, Israel

Abstract: I identify a point-symmetric structure composed of three pairs of clumps in the recently released JWST image of the ejecta of SN 1987A and argue that these pairs of clumps support the jittering jets explosion mechanism (JJEM) for SN 1987A. I compare this point-symmetric structure with the multipolar-lobe morphology of a post-asymptotic giant branch nebula. The three pairs of clumps in the post-AGB nebula are formed at the tip of jet-inflated lobes. I use this similarity to strengthen earlier claims that SN 1987A was exploded by jets in the frame of the JJEM.

Authors:Akash Garg IUCAA, Divya Rawat IUCAA, Mariano Méndez Kapteyn Astronomical Institute

Abstract: The incoming Imaging X-ray Polarimetry Explorer (IXPE) observations of X-ray binaries provide a new tool to investigate the underlying accretion geometry. Here we report the first measurements of X-ray polarization of the extra-galactic black-hole X-ray binary LMC X$-$3. We find a polarization fraction of $\sim$ 3 % at a polarization angle of $\sim 135^\circ$ in the $2-8$ keV energy band with statistical significance at the 7$\sigma$ level. This polarization measurement significantly exceeds the minimum detectable polarization threshold of 1.2 % for the source, ascertained at a 99 % confidence level within the $2-8$ keV energy band. The simultaneous spectro-polarimetric fitting of NICER, Swift/XRT, and IXPE revealed the presence of a disc with a temperature of 1 keV and a Comptonized component with a power-law index of 2.4, confirming the soft nature of the source. The polarization degree increases with energy from $\sim$3 % in the $2-5$ keV band to $\sim$8 % in the $5-8$ keV band, while the polarization angle is energy independent. The observed energy dependence and the sudden jump of polarization fraction at $\sim$ 5 keV supports the idea of a static slab coronal geometry for the comptonizing medium of LMC X$-$3. We further observed no change in the polarization properties with time over the period of the IXPE observations.

Authors:A. Manca, A. Sanna, A. Marino, T. Di Salvo, S. M. Mazzola, A. Riggio, N. Deiosso, C. Cabras, L. Burderi

Abstract: XTE J1810-189 is a Low-Mass X-ray Binary transient system hosting a neutron star, which underwent a three-month-long outburst in 2020. In order to study its spectral evolution during this outburst, we analysed all the available observations performed by NICER, in the 1-10 keV energy band. Firstly, we fitted the spectra with a thermal Comptonisation model. Our analysis revealed the lack of a significant direct emission from a black-body-like component, therefore we calculated the optical depth of the Comptonising region, deriving an upper limit of 4.5, which suggests the presence of a moderately thick corona. We also attempted to fit the spectrum with an alternative model, i.e. a cold Comptonised emission from a disc and a direct thermal component from the neutron star, finding a similarly good fit. The source did not enter a full high luminosity/soft state throughout the outburst, with a photon index ranging from 1.7 to 2.2, and an average unabsorbed flux in the 1-10 keV band of 3.6x10^(-10) erg cm^(-2) s^(-1). We searched for the presence of Fe K-shell emission lines in the range 6.4-7 keV, significantly detecting a broad component only in a couple of observations. Finally, we conducted a time-resolved spectral analysis of the detected type-I X-ray burst, observed during the outburst, finding no evidence of a photospheric radius expansion. The type-I burst duration suggests a mix of H/He fuel.

Authors:Ioannis Contopoulos, Ioannis Dimitropoulos, Vassilis Mpisketzis, Evangelos Chaniadakis

Abstract: We propose a new method for obtaining the general solution of the ideal force-free steady-state pulsar magnetosphere in 3D. We divide the magnetosphere in the regions of closed and open field lines and train two custom Physics Informed Neural Networks (PINNs) to yield the solution in each of these two regions. We also periodically adjust the shape of the separatrix between the two regions to satisfy pressure balance everywhere. Our method introduces several innovations over traditional methods that are based on numerical grids and finite differences. In particular, it introduces a proper treatment of mathematical contact discontinuities in FFE. We present preliminary results in axisymmetry which confirm the significant potential of our method.

Authors:Seshadri Majumder, Ankur Kushwaha, Santabrata Das, Anuj Nandi

Abstract: We report a comprehensive spectro-polarimetric study of the black hole binary LMC X$-3$ using simultaneous {\it IXPE}, {\it NICER} and {\it NuSTAR} observations in $0.5-20$ keV energy band. The broad-band energy spectrum ($0.5-20$ keV) with {\it NICER} and {\it NuSTAR} is well described by the disc emission of temperature $\sim 1.1$ keV and a weak Compotonizing tail beyond $\sim 10$ keV. This evidently suggests a disc-dominated spectral state of the source with disc contribution of $\sim 96\%$. The lack of variability ($rms \sim 0.5\%$) in the power density spectrum further corroborates the high/soft nature of the source. A significant polarization degree (PD) of $3.04 \pm 0.40\%$ ($ > 7\sigma$) at a polarization angle (PA) of $-44.24^{\circ} \pm 3.77^{\circ}$ ($> 7\sigma$) is found in $2-8$ keV energy range of {\it IXPE}. In addition, the degree of polarization is seen to increase with energy up to $\sim 4.35 \pm 0.98\%$ ($> 3\sigma$) in $4-8$ keV band. Further, we attempt to constrain the spin ($a_{*}$) of the source using broad-band spectral modelling that indicates a weakly rotating black hole in LMC X$-3$ with $a_{*} = 0.295_{-0.021}^{+0.008}-0.273_{-0.012}^{+0.011}$ ($90\%$ confidence). Based on the spectro-polarimetric results, we infer that the polarization in LMC X$-3$ is resulted possibly due to the combined effects of the direct and/or reflected emissions from a partially ionized disc atmosphere. Finally, we discuss the relevance of the above findings.

Authors:ANTARES Collaboration, A. Albert, S. Alves, M. André, M. Ardid, S. Ardid, J. J. Aubert, J Aublin, B. Baret, S. Basa, Y. Becherini, B. Belhorma, M. Bendahman, F. Benfenati, V. Bertin, S. Biagi, M. Bissinger, J. Boumaaza, M. Bouta, M. C. Bouwhuis, H. Brânzaş, R. Bruijn, J. Brunner, J. Busto, B. Caiffi, D. Calvo, S. Campion, A. Capone, L. Caramete, F. Carenini, J. Carr, V. Carretero, S. Celli, L. Cerisy, M. Chabab, R. Cherkaoui El Moursli, T. Chiarusi, M. Circella, J. A. B. Coelho, A. Coleiro, R. Coniglione, P. Coyle, A. Creusot, A. S. M. Cruz, A. F. Díaz, B. De Martino, C. Distefano, I. Di Palma, A. Domi, C. Donzaud, D. Dornic, D. Drouhin, T. Eberl, T. van Eeden, D. van Eijk, S. El Hedri, N. El Khayati, A. Enzenhöfer, P. Fermani, G. Ferrara, F. Filippini, L. Fusco, S. Gagliardini, J. García, C. Gatius Oliver, P. Gay, N. Geißelbrecht, H. Glotin, R. Gozzini, R. Gracia Ruiz, K. Graf, C. Guidi, L. Haegel, S. Hallmann, H. van Haren, A. J. Heijboer, Y. Hello, J. J. Hernández-Rey, J. Hößl, J. Hofestädt, F. Huang, G. Illuminati, C. W. James, B. Jisse-Jung, M. de Jong, P. de Jong, M. Kadler, O. Kalekin, U. Katz, A. Kouchner, Y. A Kovalev, Y. Y Kovalev, I. Kreykenbohm, V. Kulikovskiy, R. Lahmann, M. Lamoureux, A. Lazo, D. Lefèvre, E. Leonora, G. Levi, S. Le Stum, D. Lopez-Coto, S. Loucatos, L. Maderer, J. Manczak, M. Marcelin, A. Margiotta, A. Marinelli, J. A. Martínez-Mora, P. Migliozzi, A. Moussa, R. Muller, S. Navas, E. Nezri, B. Ó Fearraigh, E. Oukacha, A. Păun, G. E. Păvălaş, S. Peña-Martínez, M. Perrin-Terrin, V. Pestel, P. Piattelli, A. Plavin, C. Poirè, V. Popa, T. Pradier, A. Pushkarev, N. Randazzo, D. Real, S. Reck, G. Riccobene, A. Romanov, A. Sánchez-Losa, A. Saina, F. Salesa Greus, D. F. E. Samtleben, M. Sanguineti, P. Sapienza, J. Schnabel, J. Schumann, F. Schüssler, J. Seneca, M. Spurio, Th. Stolarczyk, M. Taiuti, Y. Tayalati, S. J. Tingay, S. Troitsky, B. Vallage, G. Vannoye, V. Van Elewyck, S. Viola, D. Vivolo, J. Wilms, S. Zavatarelli, A. Zegarelli, J. D. Zornoza, J. Zúñiga, OVRO Collaboration, :, T. Hovatta, S. Kiehlmann, I. Liodakis, V. Pavlidou, A. C. S Readhead

Abstract: Active galaxies, especially blazars, are among the most promising neutrino source candidates. To date, ANTARES searches for these objects considered GeV-TeV $\gamma$-ray bright blazars. Here, a statistically complete radio-bright blazar sample is used as the target for searches of origins of neutrinos collected by the ANTARES neutrino telescope over 13 years of operation. The hypothesis of a neutrino-blazar directional correlation is tested by pair counting and by a complementary likelihood-based approach. The resulting post-trial $p$-value is $3.0\%$ ($2.2\sigma$ in the two-sided convention), possibly indicating a correlation. Additionally, a time-dependent analysis is performed to search for temporal clustering of neutrino candidates as a mean of detecting neutrino flares in blazars. None of the investigated sources alone reaches a significant flare detection level. However, the presence of 18 sources with a pre-trial significance above $3\sigma$ indicates a $p=1.4\%$ ($2.5\sigma$ in the two-sided convention) detection of a time-variable neutrino flux. An \textit{a posteriori} investigation reveals an intriguing temporal coincidence of neutrino, radio, and $\gamma$-ray flares of the J0242+1101 blazar at a $p=0.5\%$ ($2.9\sigma$ in the two-sided convention) level. Altogether, the results presented here suggest a possible connection of neutrino candidates detected by the ANTARES telescope with radio-bright blazars.

Authors:Zsófia V. Kovács-Stermeczky, József Vinkó

Abstract: A Tidal Disruption Event (TDE) occurs when a supermassive black hole tidally disrupt a nearby passing star. The fallback accretion rate of the disrupted star may exceed the Eddington limit, which induces a supersonic outflow and a burst of luminosity, similar to an explosive event. Thus, TDEs can be detected as very luminous transients, and the number of observations for such events is increasing rapidly. In this paper we fit 20 TDE light curves with TiDE, a new public, object-oriented code designed to model optical TDE light curves. We compare our results with those obtained by the popular MOSFiT and the recently developed TDEmass codes, and discuss the possible sources of differences.

Authors:Yu Zhao, Xiao-Hong Yang, Li Xue, Shuang-Liang Li

Abstract: According to the standard thin disc theory, it is predicted that the radiation-pressure-dominated inner region of a thin disc is thermally unstable, while observations suggest that it is common for a thin disc of more than 0.01 Eddington luminosity to be in a thermally stable state. Previous studies have suggested that magnetically-driven winds are potential to suppress instability. In this work, we implement one-dimensional global simulations of the thin accretion disc to study the effects of magnetically-driven winds on thermal instability. The winds play a role in transferring the angular momentum of the disc and cooling the disc. When the mass outflow rate of winds is low, the important role of winds is to transfer the angular momentum and then shorten the outburst period. When the winds have a high mass outflow rate, they can calm down the thermal instability. We also explore the parameter space of the magnetic field strength and the mass loading parameter.

Authors:A. M. Steane

Abstract: We study the gravitational bremsstrahlung owing to collisions mediated by a $1/r$ potential. We combine classical and first order Born approximation results in order to construct an approximate gravitational `Gaunt factor' for the total emitted energy. We also obtain the cross-section with an angular momentum cut-off, and hence the cross-section for emission via close hyperbolic encounters in a gravitating cluster. These effects are the dominant source of very high frequency gravitational noise in the solar system. The total gravitational wave power of the Sun is $76\pm 20\,$MW.

Authors:Yong Yuan, Xi-Long Fan, Hou-Jun Lv, Yang-Yi Sun, Kai Lin

Abstract: The gravitational waves (GW) from core-collapse supernovae (CCSN) have been proposed as a probe to investigate physical properties inside of the supernova. However, how to search and extract the GW signals from core-collapse supernovae remains an open question due to its complicated time-frequency structure. In this paper, we applied the Ensemble Empirical Mode Decomposition (EEMD) method to decompose and reconstruct simulated GW data generated by magnetorotational mechanism and neutrino-driven mechanism within the advanced LIGO, using the match score as the criterion for assessing the quality of the reconstruction. The results indicate that by decomposing the data, the sum of the first six intrinsic mode functions (IMFs) can be used as the reconstructed waveform. To determine the probability that our reconstructed waveform corresponds to a real GW waveform, we calculated the false alarm probability of reconstruction (FAPR). By setting the threshold of the match score to be 0.75, we obtained FAPR of GW sources at a distance of 5 kpc and 10 kpc to be $1\times10^{-2}$ and $3\times10^{-2}$ respectively. If we normalize the maximum amplitude of the GW signal to $5\times10^{-21}$, the FAPR at this threshold is $4\times10^{-3}$. Furthermore, in our study, the reconstruction distance is not equivalent to the detection distance. When the strain of GW reaches $7 \times 10^{-21}$, and the match score threshold is set at 0.75, we can reconstruct GW waveform up to approximately 37 kpc.

Authors:Fatemeh Hossein Nouri, Agnieszka Janiuk

Abstract: The merger of supermassive black holes (BBH) produces mHz gravitational waves (GW), which are potentially detectable by future Laser Interferometer Space Antenna (LISA). Such binary systems are usually embedded in an accretion disk environment at the centre of the active galactic nuclei (AGN). Recent studies suggest the plasma environment imposes measurable imprints on the GW signal if the mass ratio of the binary is around q $ \sim10^{-4}-10^{-3}$. The effect of the gaseous environment on the GW signal is strongly dependent on the disk's parameters, therefore it is believed that future low-frequency GW detections will provide us with precious information about the physics of AGN accretion disks. We investigate this effect by measuring the disk torques on the binary system by modelling several magnetized tori. Using GRMHD HARM-COOL code, we perform 2D simulations of weakly-magnetized thin accretion disks, with a possible truncation and transition to advection-dominated accretion flow (ADAF). In our numerical simulations, we study the angular momentum transport and turbulence generated by the magnetorotational instability (MRI). We quantify the disk's effective alpha viscosity and its evolution over time. We apply our numerical results to estimate the relativistic viscous torque and GW phase shift due to the gas environment.

Authors:Pin Gao, Xi-Long Fan, Zhou-Jian Cao, Xue-Hao Zhang

Abstract: Resolving individual gravitational waves from tens of millions of double white dwarf (DWD) binaries in the Milky Way is a challenge for future space-based gravitational wave detection programs. By using previous data to define the priors for the next search, we propose an accelerated approach of searching the DWD binaries and demonstrate its efficiency based on the GBSIEVER detection pipeline. Compared to the traditional GBSIEVER method, our method can obtain $\sim 50\%$ of sources with 2.5\% of the searching time for LDC1-4 data. In addition, we find that both methods have a similar ability to detect the Milky Way structure by their confirmed sources. The relative error of distance and chirp mass is about 20\% for DWD binaries whose gravitational wave frequency is higher than $4\times10^{-3}$ Hz, even if they are close to the Galactic center. Finally, we propose a signal-to-noise ratio (SNR) threshold for LISA to confirm the detection of DWD binaries. The threshold should be 16 when the gravitational wave frequency is lower than $4\times10^{-3}$ Hz and 9 when the frequency range is from $4\times10^{-3}$ Hz to $1.5\times10^{-2}$ Hz.

Authors:Xilu Wang, Rebecca Surman

Abstract: This chapter discusses three nucleosynthesis processes involved in producing heavy nuclei beyond the iron group that are influenced or shaped by neutrino interactions: the v process, the vp process and the r process. These processes are all related to explosive events involving compact objects, such as core-collapse supernovae and binary neutron star mergers, where an abundant amount of neutrinos are emitted. The interactions of the neutrinos with nucleons and nuclei through both charged-current and neutral-current reactions play a crucial role in the nucleosynthesis processes. During the propagation of neutrinos inside the nucleosynthesis sites, neutrinos may undergo flavor oscillations that can also potentially affect the nucleosynthesis yields. Here we provide a general overview of the possible effects of neutrinos and neutrino flavor conversions on these three heavy-element nucleosynthesis processes.

Authors:Ze-Nan Liu, Jin-Jun Geng, Yuan-Pei Yang, Wei-Yang Wang, Zi-Gao Dai

Abstract: Fast radio bursts (FRBs) are extragalactic radio transients with extremely high brightness temperature, which strongly suggests the presence of coherent emission mechanisms. In this study, we introduce a novel radiation mechanism for FRBs involving coherent Cherenkov radiation (ChR) emitted by bunched particles that may originate within the magnetosphere of a magnetar. We assume that some relativistic particles are emitted from the polar cap of a magnetar and move along magnetic field lines through a charge-separated magnetic plasma, emitting coherent ChR along their trajectory. The crucial condition for ChR to occur is that the refractive index of the plasma medium, denoted as $n_r$, must satisfy the condition $n_r^2 > 1$. We conduct comprehensive calculations to determine various characteristics of ChR, including its characteristic frequency, emission power, required parallel electric field, and coherence factor. Notably, our proposed bunched coherent ChR mechanism has the remarkable advantage of generating a narrower-band spectrum. Furthermore, a frequency downward drifting pattern, and $\sim100\%$ linearly polarized emission can be predicted within the framework of this emission mechanism.

Authors:Roberto Serafinelli, Andrea Marinucci, Alessandra De Rosa, Stefano Bianchi, Riccardo Middei, Giorgio Matt, James N. Reeves, Valentina Braito, Francesco Tombesi, Vittoria E. Gianolli, Adam Ingram, Frédéric Marin, Pierre-Olivier Petrucci, Daniele Tagliacozzo, Francesco Ursini

Abstract: MCG-5-23-16 is a Seyfert 1.9 galaxy at redshift z=0.00849. We analyse here the X-ray spectra obtained with XMM-Newton and NuSTAR data, which are the first contemporaneous observations with these two X-ray telescopes. Two reflection features, producing a narrow core and a broad component of the Fe K$\alpha$, are clearly detected in the data. The analysis of the broad iron line shows evidence of a truncated disc with inner radius $R_{\rm in}=40^{+23}_{-16}$ $R_g$ and an inclination of $41^{+9}_{-10}$ $^\circ$. The high quality of the NuSTAR observations allows us to measure a high energy cut-off at $E_{\rm cut}=131^{+10}_{-9}$ keV. We also analyse the RGS spectrum, finding that the soft X-ray emission is produced by two photoionised plasma emission regions, with different ionisation parameters and similar column densities. Remarkably, the source only shows moderate continuum flux variability, keeping the spectral shape roughly constant in a time scale of $\sim20$ years.

Authors:Xiao-Song Hu, Ben-Yang Zhu, Tian-Ci Liu, Yun-Feng Liang

Abstract: Electrons and positrons produced in dark matter annihilation can generate secondary emission through synchrotron and IC processes, and such secondary emission provides a possible means to detect DM particles with masses beyond the detector's energy band. The secondary emission of heavy dark matter (HDM) particles in the TeV-PeV mass range lies within the Fermi-LAT energy band. In this paper, we utilize the Fermi-LAT observations of dwarf spheroidal (dSph) galaxies to search for annihilation signals of HDM particles. We consider the propagation of $e^+/e^-$ produced by DM annihilation within the dSphs, derive the electron spectrum of the equilibrium state by solving the propagation equation, and then compute the gamma-ray signals produced by the $e^+/e^-$ population through the IC and synchrotron processes. We do not detect any significant HDM signal. By assuming a magnetic field strength of $B=1\,{\rm \mu G}$ and a diffusion coefficient of $D_0 = 3\times10^{28}\,{\rm cm^{2}s^{-1}}$ of the dSphs, we place limits on the annihilation cross section for HDM particles. Our results are weaker than the previous limits given by the VERITAS observations of dSphs, but are comparable to those derived from the IceCube observations of dSphs. As a complement, we also search for the prompt $\gamma$-rays produced by DM annihilation and give limits on the cross section in the 10-$10^5$ GeV mass range. Consequently, in this paper we obtain the upper limits on the DM annihilation cross section for a very wide mass range from 10 GeV to 100 PeV in a unified framework of the Fermi-LAT data analysis.

Authors:Atreya Acharyya, Marcos Santander

Abstract: High-energy neutrinos originating in astrophysical sources should be accompanied by gamma-rays at production. Depending on the properties of the emission environment and the distance of the source to the Earth, these gamma-rays may be observed directly, or through the detection of lower energy photons that result from interactions with the intervening radiation fields. In this work, we present an automated tool that aims at using data from the Fermi-Large Area Telescope to identify multiwavelength counterparts to astrophysical neutrino events. The main goal of this tool is to enable prompt follow-up observations with ground-based and space-based observatories in order to help pinpoint the neutrino source.

Authors:The Pierre Auger Collaboration, A. Abdul Halim, P. Abreu, M. Aglietta, I. Allekotte, K. Almeida Cheminant, A. Almela, R. Aloisio, J. Alvarez-Muñiz, J. Ammerman Yebra, G. A. Anastasi, L. Anchordoqui, B. Andrada, S. Andringa, Anukriti, C. Aramo, P. R. Araújo Ferreira, E. Arnone, J. C. Arteaga Velázquez, P. Assis, G. Avila, E. Avocone, A. M. Badescu, A. Bakalova, F. Barbato, A. Bartz Mocellin, J. A. Bellido, C. Berat, M. E. Bertaina, G. Bhatta, M. Bianciotto, P. L. Biermann, V. Binet, K. Bismark, T. Bister, J. Biteau, J. Blazek, C. Bleve, J. Blümer, M. Boháčová, D. Boncioli, C. Bonifazi, L. Bonneau Arbeletche, N. Borodai, J. Brack, P. G. Brichetto Orchera, F. L. Briechle, A. Bueno, S. Buitink, M. Buscemi, A. Bwembya, M. Büsken, K. S. Caballero-Mora, S. Cabana-Freire, L. Caccianiga, R. Caruso, A. Castellina, F. Catalani, G. Cataldi, L. Cazon, M. Cerda, A. Cermenati, J. A. Chinellato, J. Chudoba, L. Chytka, R. W. Clay, A. C. Cobos Cerutti, R. Colalillo, A. Coleman, M. R. Coluccia, R. Conceição, A. Condorelli, G. Consolati, M. Conte, F. Convenga, D. Correia dos Santos, P. J. Costa, C. E. Covault, M. Cristinziani, C. S. Cruz Sanchez, S. Dasso, K. Daumiller, B. R. Dawson, R. M. de Almeida, J. de Jesús, S. J. de Jong, J. R. T. de Mello Neto, I. De Mitri, J. de Oliveira, D. de Oliveira Franco, F. de Palma, V. de Souza, B. P. de Souza de Errico, E. De Vito, A. Del Popolo, O. Deligny, N. Denner, L. Deval, A. di Matteo, M. Dobre, C. Dobrigkeit, J. C. D'Olivo, L. M. Domingues Mendes, J. C. dos Anjos, R. C. dos Anjos, J. Ebr, F. Ellwanger, M. Emam, R. Engel, I. Epicoco, M. Erdmann, A. Etchegoyen, C. Evoli, H. Falcke, J. Farmer, G. Farrar, A. C. Fauth, N. Fazzini, F. Feldbusch, F. Fenu, A. Fernandes, B. Fick, J. M. Figueira, A. Filipčič, T. Fitoussi, B. Flaggs, T. Fodran, T. Fujii, A. Fuster, C. Galea, C. Galelli, B. García, C. Gaudu, H. Gemmeke, F. Gesualdi, A. Gherghel-Lascu, P. L. Ghia, U. Giaccari, J. Glombitza, F. Gobbi, F. Gollan, G. Golup, J. P. Gongora, J. M. González, N. González, I. Goos, A. Gorgi, M. Gottowik, T. D. Grubb, F. Guarino, G. P. Guedes, E. Guido, M. Gómez Berisso, P. F. Gómez Vitale, D. Góra, S. Hahn, P. Hamal, M. R. Hampel, P. Hansen, D. Harari, V. M. Harvey, A. Haungs, T. Hebbeker, C. Hojvat, P. Horvath, M. Hrabovský, T. Huege, J. R. Hörandel, A. Insolia, P. G. Isar, P. Janecek, J. A. Johnsen, J. Jurysek, K. H. Kampert, B. Keilhauer, A. Khakurdikar, V. V. Kizakke Covilakam, H. O. Klages, M. Kleifges, F. Knapp, N. Kunka, B. L. Lago, N. Langner, M. A. Leigui de Oliveira, Y. Lema-Capeans, A. Letessier-Selvon, I. Lhenry-Yvon, L. Lopes, L. Lu, Q. Luce, J. P. Lundquist, A. Machado Payeras, M. Majercakova, D. Mandat, B. C. Manning, P. Mantsch, S. Marafico, F. M. Mariani, A. G. Mariazzi, I. C. Mariş, G. Marsella, D. Martello, S. Martinelli, M. A. Martins, O. Martínez Bravo, H. J. Mathes, J. Matthews, G. Matthiae, E. Mayotte, S. Mayotte, P. O. Mazur, G. Medina-Tanco, J. Meinert, D. Melo, A. Menshikov, C. Merx, S. Michal, M. I. Micheletti, L. Miramonti, S. Mollerach, F. Montanet, L. Morejon, C. Morello, K. Mulrey, R. Mussa, W. M. Namasaka, S. Negi, L. Nellen, K. Nguyen, G. Nicora, M. Niechciol, D. Nitz, D. Nosek, V. Novotny, L. Nožka, A. Nucita, L. A. Núñez, C. Oliveira, M. Palatka, J. Pallotta, S. Panja, G. Parente, T. Paulsen, J. Pawlowsky, M. Pech, R. Pelayo, L. A. S. Pereira, E. E. Pereira Martins, J. Perez Armand, L. Perrone, S. Petrera, C. Petrucci, T. Pierog, M. Pimenta, M. Platino, B. Pont, M. Pothast, M. Pourmohammad Shahvar, P. Privitera, M. Prouza, A. Puyleart, C. Pérez Bertolli, J. Pękala, S. Querchfeld, J. Rautenberg, D. Ravignani, J. V. Reginatto Akim, M. Reininghaus, J. Ridky, F. Riehn, M. Risse, V. Rizi, W. Rodrigues de Carvalho, E. Rodriguez, J. Rodriguez Rojo, M. J. Roncoroni, S. Rossoni, M. Roth, E. Roulet, A. C. Rovero, P. Ruehl, A. Saftoiu, M. Saharan, F. Salamida, H. Salazar, G. Salina, J. D. Sanabria Gomez, E. M. Santos, E. Santos, F. Sarazin, R. Sarmento, R. Sato, P. Savina, V. Scherini, H. Schieler, M. Schimassek, M. Schimp, D. Schmidt, O. Scholten, H. Schoorlemmer, P. Schovánek, F. G. Schröder, J. Schulte, T. Schulz, C. M. Schäfer, S. J. Sciutto, M. Scornavacche, A. Segreto, S. Sehgal, S. U. Shivashankara, G. Sigl, G. Silli, O. Sima, F. Simon, R. Smau, P. Sommers, J. F. Soriano, R. Squartini, M. Stadelmaier, S. Stanič, J. Stasielak, P. Stassi, M. Straub, S. Strähnz, T. Suomijärvi, A. D. Supanitsky, Z. Svozilikova, Z. Szadkowski, F. Sánchez, F. Tairli, A. Tapia, C. Taricco, C. Timmermans, O. Tkachenko, P. Tobiska, C. J. Todero Peixoto, B. Tomé, Z. Torrès, A. Travaini, P. Travnicek, C. Trimarelli, M. Tueros, M. Unger, L. Vaclavek, M. Vacula, J. F. Valdés Galicia, L. Valore, E. Varela, D. Veberič, C. Ventura, I. D. Vergara Quispe, V. Verzi, J. Vicha, J. Vink, J. Vlastimil, S. Vorobiov, A. Vásquez-Ramírez, C. Watanabe, A. A. Watson, A. Weindl, L. Wiencke, H. Wilczyński, D. Wittkowski, B. Wundheiler, B. Yue, A. Yushkov, O. Zapparrata, E. Zas, D. Zavrtanik, M. Zavrtanik, R. Šmída

Abstract: Operating since 2004, the Pierre Auger Observatory has led to major advances in our 8 understanding of the ultra-high-energy cosmic rays. The latest findings have revealed new insights 9 that led to the upgrade of the Observatory, with the primary goal of obtaining information on the 10 primary mass of the most energetic cosmic rays on a shower-by-shower basis. In the framework of the 11 upgrade, called AugerPrime, the 1660 water-Cherenkov detectors of the surface array are equipped 12 with plastic scintillators and radio antennas, allowing us to enhance the composition sensitivity. 13 To accommodate new detectors and to increase experimental capabilities, the electronics is also 14 upgraded. This includes better timing with up-to-date GPS receivers, higher sampling frequency, 15 increased dynamic range, and more powerful local processing of the data. In this paper, the design 16 characteristics of the new electronics and the enhanced dynamic range will be described. The 17 manufacturing and test processes will be outlined and the test results will be discussed. The 18 calibration of the SD detector and various performance parameters obtained from the analysis of 19 the first commissioning data will also be presented.

Authors:Dongzi Li, Ue-Li Pen

Abstract: A fast radio burst (FRB) localized to a globular cluster (GC) challenges FRB models involving ordinary young magnetars. In this paper, we examine the rapid spindown millisecond neutron star (NS) scenario, which favours the dynamic environment in GCs. Fast spindown corresponds to a larger magnetic field than regular millisecond pulsars, which empirically favours giant pulse (GP) emission. The kinetic energy in millisecond NSs can readily exceed the magnetic energy in magnetars. The high inferred isotropic luminosity of most FRBs is challenging to explain in spin-down powered pulsars. A recent observation of a GP from the Crab pulsar, on the other hand, suggests highly Doppler-beamed emission, making the required energy orders of magnitude smaller than estimated with isotropic assumptions. Considering this strong beaming effect, GPs from a recycled pulsar with a modest magnetic field could explain the energetics and burst rates for a wide range of FRBs. The short life span accounts for a paucity of bright FRBs in the Milky Way neighbourhood. We point out that tidal disruption spin-up from a main sequence star can provide sufficient accretion rate to recycle a NS with mild magnetic field. It can also explain the observed source density and the spatial offset in the GC for FRB 20200120E. Frequency variation in the scattering tail for some of the brightest FRBs is expected in this scenario.

Authors:Petros Stefanou, Jorge F. Urbán, José A. Pons

Abstract: In this study, Physics-Informed Neural Networks (PINNs) are skilfully applied to explore a diverse range of pulsar magneto-spheric models, specifically focusing on axisymmetric cases. The study successfully reproduced various axisymmetric models found in the literature, including those with non-dipolar configurations, while effectively characterizing current sheet features. Energy losses in all studied models were found to exhibit reasonable similarity, differing by no more than a factor of three from the classical dipole case. This research lays the groundwork for a reliable elliptic Partial Differential Equation solver tailored for astrophysical problems. Based on these findings, we foresee that the utilization of PINNs will become the most efficient approach in modelling three-dimensional magnetospheres. This methodology shows significant potential and facilitates an effortless generalization, contributing to the advancement of our understanding of pulsar magnetospheres.

Authors:Kaho Tse, Duncan K. Galloway, Alexander Heger

Abstract: We report the detection of millihertz quasi-periodic oscillations ($\mathrm{mHz}$ QPOs) from the low-mass X-ray binary XTE 1701$-$462. The discovery came from a search of the legacy data set of the Rossi X-ray Timing Explorer, in order to detect the periodic signals in all observations of sources exhibiting thermonuclear bursts. We found that $47$ out of $860$ observations of XTE 1701$-$462; covering the 2006--7 outburst exhibits signals with a significance above the detection threshold, which was determined separately for each observation via a Monte Carlo approach. We chose the four strongest candidates, each with maximum power exceeding $4\sigma$ of the simulated wavelet noise power distribution, to demonstrate the properties of the QPOs. The frequencies of the signals in the four observations are $\sim 3.5\;\text{to}\;5.6\; \mathrm{mHz}$, and the fractional R.M.S. amplitudes vary between $0.74 \pm 0.05\,\%$ and $3.54 \pm 0.04\,\%$. Although previously reported signals in other sources typically disappear immediately before a burst, we do not observe this behaviour in XTE 1701$-$462. Instead, we found that the QPOs and bursts occurred in separate accretion regimes. When the persistent luminosity dropped near the end of the outburst, the source showed bursts and no QPOs were detected, which is the behaviour predicted by theory for the transition from stable to unstable burning. On the basis of this new detection, we reassess the cases for identifying these $\mathrm{mHz}$ QPOs in this and other sources as arising from marginally stable burning.

Authors:Liyi Gu, Jelle Kaastra, Daniele Rogantini, Missagh Mehdipour, Anna Juranova, Elisa Costantini, Chen Li

Abstract: We present an investigation into the spectroscopic properties of non-equilibrium photoionization processes operating in a time-evolving mode. Through a quantitative comparison between equilibrium and time-evolving models, we find that the time-evolving model exhibits a broader distribution of charge states compared to the equilibrium model, accompanied by a slight shift in the peak ionization state depending on the source variability and gas density. The time-evolving code, tpho in SPEX, has been successfully employed to analyze the spectral properties of warm absorbers in the Seyfert galaxy NGC 3783. The incorporation of variability in the tpho model improves the fits of the time-integrated spectra, providing more accurate descriptions to the average charge states of several elements, in particular for Fe which is peaked around Fe XIX. The inferred densities and distances of the relevant X-ray absorber components are estimated to be approximately a few 1E11 per cubic meter and less than 1 pc, respectively. Furthermore, the updated fit suggests a potential scenario in which the observed absorbers are being expelled from the central AGN at the escape velocities. This implies that these absorbers might not play a significant role in the AGN feedback mechanism.

Authors:Ayako T. Ishii, Yuki Takei, Daichi Tsuna, Toshikazu Shigeyama, Koh Takahashi

Abstract: Some supernovae (SNe), such as Type IIn SNe, are powered by collision of the SN ejecta with a dense circumstellar matter (CSM). Their emission spectra show characteristic line shapes of combined broad emission and narrow P-Cyg lines, which should closely relate to the CSM structure and the mass-loss mechanism that creates the dense CSM. We quantitatively investigate the relationship between the line shape and the CSM structure by Monte Carlo radiative transfer simulations, considering two representative cases of dense CSM formed by steady and eruptive mass loss. Comparing the H$\alpha$ emission between the two cases, we find that a narrow P-Cyg line appears in the eruptive case while it does not appear in the steady case, due to the difference in the velocity gradient in the dense CSM. We also reproduce the blue-shifted photon excess observed in some SNe IIn, which is formed by photon transport across the shock wave and find the relationship between the velocity of the shocked matter and the amount of the blue shift of the photon excess. We conclude that the presence or absence of narrow P-Cyg lines can distinguish the mass loss mechanism, and suggest high-resolution spectroscopic observations with $\lambda/ \Delta \lambda \gtrsim 10^4$ after the light curve peak for applying this diagnostic method.

Authors:Felix Riehn, Ralph Engel, Anatoli Fedynitch

Abstract: Current simulations of air showers produced by ultra-high energy cosmic rays (UHECRs) do not satisfactorily describe recent experimental data, particularly when looking at the muonic shower component relative to the electromagnetic one. Discrepancies can be seen in both average values and on an individual shower-by-shower basis. It is thought that the muonic part of the air showers isn't accurately represented in simulations, despite various attempts to boost the number of muons within standard hadronic interaction physics. In this study, we investigate whether modifying the final state of events created with Sibyll~2.3d in air shower simulations can achieve a more consistent description of the muon content observed in experimental data. We create several scenarios where we separately increase the production of baryons, $\rho^0$, and strange particles to examine their impact on realistic air shower simulations. Our results suggest that these ad-hoc modifications can improve the simulations, providing a closer match to the observed muon content in air showers. One side-effect of the increased muon production in the considered model versions is a smaller difference in the predicted total muon numbers for proton and iron showers. However, more research is needed to find out whether any of these adjustments offers a realistic solution to the mismatches seen in data, and to identify the precise physical process causing these changes in the model. We hope that these modified model versions will also help to develop improved machine-learning analyses of air shower data and to estimate sys.{} uncertainties related to shortcomings of hadronic interaction models.

Authors:E. S. Kammoun, L. Robin, I. E. Papadakis, M. Dovčiak, C. Panagiotou

Abstract: In this paper, we present an updated version of our model (KYNXiltr) which considers thermal reverberation of a standard Novikov-Thorne accretion disc illuminated by an X-ray point-like source. Previously, the model considered only two cases of black hole spins, and assumed a colour correction factor $f_{\rm col} = 2.4$. Now, we extend the model to any spin value and colour correction. In addition, we consider two scenarios of powering the X-ray corona, either via accretion, or external to the accretion disc. We use KYNXiltr to fit the observed time lags obtained from intense monitoring of four local Seyfert galaxies (NGC 5548, NGC 4395, Mrk 817, and Fairall 9). We consider various combinations of black hole spin, colour correction, corona height, and fraction of accretion power transferred to the corona. The model fits well the overall time-lags spectrum in these sources (for a large parameter space). For NGC 4593 only, we detect a significant excess of delays in the U-band. The contribution of the diffuse BLR emission in the time-lags spectrum of this source is significant. It is possible to reduce the large best-fitting parameter space by combining the results with additional information, such as the observed Eddington ratio and average X-ray luminosity. We also provide an update to the analytic expression provided by Kammoun et al., for an X-ray source that is not powered by the accretion process, which can be used for any value of colour correction, and for two values of the black hole spin (0 and 0.998).

Authors:Hiroki Yoneda, Felix Aharonian, Paolo Coppi, Thomas Siegert, Tadayuki Takahashi

Abstract: De-excitation gamma-ray lines, produced by nuclei colliding with protons, provide information about astrophysical environments where particles have kinetic energies of $10-100$ MeV per nucleon. In general, such environments can be categorized into two types: the interaction between non-thermal MeV cosmic rays and ambient gas, and the other is thermal plasma with a temperature above a few MeV. In this paper, we focus on the latter type and investigate the production of de-excitation gamma-ray lines in very hot thermal plasma, especially the dependence of the line profile on the plasma temperature. We have calculated the line profile of prompt gamma rays from $^{12}$C and $^{16}$O and found that when nuclei have a higher temperature than protons, gamma-ray line profiles can have a complex shape unique to each nucleus species. This is caused by anisotropic gamma-ray emission in the nucleus rest frame. We propose that the spectroscopy of nuclear de-excitation gamma-ray lines may enable to probe energy distribution in very hot astrophysical plasmas. This diagnostics can be a new and powerful technique to investigate the physical state of a two-temperature accretion flows onto a black hole, especially the energy distributions of the protons and nuclei, which are difficult to access for any other diagnostics.

Authors:Jialian Liu, Xiaofeng Wang, Alexei V. Filippenko, Thomas G. Brink, Yi Yang, Weikang Zheng, Hanna Sai, Gaobo Xi, Shengyu Yan, Nancy Elias-Rosa, Wenxiong Li, Xiangyun Zeng, Abdusamatjan Iskandar

Abstract: Late-time spectra of Type Ia supernovae (SNe Ia) are important in clarifying the physics of their explosions, as they provide key clues to the inner structure of the exploding white dwarfs. We examined late-time optical spectra of 36 SNe Ia, including five from our own project (SNe 2019np, 2019ein, 2021hpr, 2021wuf, and 2022hrs), with phase coverage of $\sim 200$ to $\sim 400$ days after maximum light. At this late phase, the outer ejecta have become transparent and the features of inner iron-group elements emerge in the spectra. Based on multicomponent Gaussian fits and reasonable choices for the pseudocontinuum around Ni and Fe emission features, we get reliable estimates of the Ni to Fe ratio, which is sensitive to the explosion models of SNe Ia. Our results show that the majority (about 67%) of our SNe Ia are more consistent with the sub-Chandrasekhar-mass (i.e., double-detonation) model, although they could be affected by evolutionary or ionisation effects. Moreover, we find that the Si II $\lambda$6355 velocity measured around the time of maximum light tends to increase with the Ni to Fe ratio for the subsample with either redshifted or blueshifted nebular velocities, suggesting that progenitor metallicity might play an important role in accounting for the observed velocity diversity of SNe Ia.

Authors:Christine E. Collins, Luke J. Shingles, Andreas Bauswein, Stuart A. Sim, Theodoros Soultanis, Vimal Vijayan, Andreas Floers, Oliver Just, Gerrit Leck, Gabriel Martínez-Pinedo, Albert Sneppen, Darach Watson, Zewei Xiong

Abstract: Recent analysis of the kilonova, AT2017gfo, has indicated that this event was highly spherical. This may challenge hydrodynamics simulations of binary neutron star mergers, which usually predict a range of asymmetries, and radiative transfer simulations show a strong direction dependence. Here we investigate whether the synthetic spectra from a 3D kilonova simulation of asymmetric ejecta from a hydrodynamical merger simulation can be compatible with the observational constraints suggesting a high degree of sphericity in AT2017gfo. Specifically, we determine whether fitting a simple P-Cygni line profile model leads to a value for the photospheric velocity that is consistent with the value obtained from the expanding photosphere method. We would infer that our kilonova simulation is highly spherical at early times, when the spectra resemble a blackbody distribution. The two independently inferred photospheric velocities can be very similar, implying a high degree of sphericity, which can be as spherical as inferred for AT2017gfo, demonstrating that the photosphere can appear spherical even for asymmetrical ejecta. The last-interaction velocities of radiation escaping the simulation show a high degree of sphericity, supporting the inferred symmetry of the photosphere. We find that when the synthetic spectra resemble a blackbody the expanding photosphere method can be used to obtain an accurate luminosity distance (within 4-7 per cent).

Authors:Richard Anantua, Angelo Ricarte, George Wong, Razieh Emami, Roger Blandford, Lani Oramas, Hayley West, Joaquin Duran, Brandon Curd

Abstract: Horizon-scale observations of the jetted active galactic nucleus M87 are compared with simulations spanning a broad range of dissipation mechanisms and plasma content in three-dimensional general relativistic flows around spinning black holes. Observations of synchrotron radiation from radio to X-ray frequencies can be compared with simulations by adding prescriptions specifying the relativistic electron-plus-positron distribution function and associated radiative transfer coefficients. A suite of time-varying simulations with various spins and plasma magnetizations is chosen to represent distinct possibilities for the M87 jet/accretion flow/black hole (JAB) system. We then input turbulent heating and equipartition-based emission prescriptions (and piecewise combinations thereof) in the time-dependent 3D simulations, in which jet morphology, polarization and variation are "observed" and compared with real observations so as to try to infer the rules that govern the polarized emissivity. The models in this paper support a magnetically arrested disk (MAD) with several possible spin/emission model combinations supplying the jet in M87, whose inner jet and black hole shadow have been observed down to the photon ring at 230 GHz by the Event Horizon Telescope (EHT). We also show that some MAD cases that are dominated by intrinsic circular polarization have near-linear V/I dependence on unpaired electron or positron content while SANE polarization exhibits markedly greater positron-dependent Faraday effects -- future probes of the SANE/MAD dichotomy and plasma content with the EHT. This is the second work in a series also applying the "observing" simulations methodology to near-horizon regions of supermassive black holes in Sgr A* and 3C 279.

Authors:Elias R. Most, Alexander A. Philippov

Abstract: The presence of magnetic fields in the late inspiral of black hole -- neutron star binaries could lead to potentially detectable electromagnetic precursor transients. Using general-relativistic force-free electrodynamics simulations, we investigate pre-merger interactions of the common magnetosphere of black hole -- neutron star systems. We demonstrate that these systems can feature copious electromagnetic flaring activity, which we find depends on the magnetic field orientation but not on black hole spin. Due to interactions with the surrounding magnetosphere, these flares could lead to Fast Radio Burst-like transients, as well as X-ray emission. Assuming interactions of the flares with the orbital current sheet as the main driver of coherent emission at low frequencies, for field strengths $B_\ast \simeq 10^{12}\, \rm G$ at the surface of the neutron star, we estimate peak frequencies above $9\, \rm GHz$ and $\mathcal{L}_{\rm EM} \lesssim 10^{41}\, \rm erg/ s$ as an upper bound for the luminosity.

Authors:A. Reimer, L. Merten, M. Boughelilba, P. Da Vela, S. Vorobiov, J. P. Lundquist

Abstract: In order to understand observable signatures from putative cosmic-ray (CR) sources in-source acceleration of particles, their energy and time-dependent transport including interactions in an evolving environment and their escape from source have to be considered, in addition to source-to-Earth propagation. We present the code CR-ENTREES (Cosmic-Ray ENergy TRansport in timE-Evolving astrophysical Settings) that evolves the coupled time- and energy-dependent kinetic equations for cosmic-ray nucleons, pions, muons, electrons, positrons, photons and neutrinos in a one-zone setup of (possibly) non-constant size, with user-defined particle and photon injection laws. All relevant interactions, particle/photon escape and adiabatic losses are considered in a radiation-dominated, magnetized astrophysical environment that is itself evolving in time. Particle and photon interactions are pre-calculated using event generators assuring an accurate interactions and secondary particle production description. We use the matrix multiplication method for fast radiation and particle energy transport which allows also an efficient treatment of transport non-linearities due to the produced particles/photons being fed back into the simulation chain. Examples for the temporal evolution of the non-thermal emission from AGN jet-like systems with focus on proton-initiated pair cascades inside an expanding versus straight jet emission region, are further presented.

Authors:Kaushik Chatterjee, Dipak Debnath, Sujoy Kumar Nath, Hsiang-Kuang Chang

Abstract: The transient Galactic black hole candidate MAXI J0637-430 went through an outburst in 2019--20 for the very first time. This outburst was active for almost 6 months from November 2019 to May 2020. We study the spectral properties of this source during that outburst using archival data from NICER, Swift, and NuSTAR satellites/instruments. We have analyzed the source during 6 epochs on which simultaneous NICER--NuSTAR and Swift/XRT--NuSTAR data were available. Using both phenomenological and physical model fitting approaches, we analyzed the spectral data in the broad $0.7-70$ keV energy band. We first used a combination of disk blackbody with power-law, disk blackbody with broken power-law, and disk blackbody with power-law and bmc models. For a better understanding of the accretion picture, e.g., understanding how the accretion rates change with the changing size of the perceived Compton cloud, we used the two-component advective flow (TCAF) model with broken power-law, TCAF with power-law and bmc models. For last 3 epochs, the diskbb+power-law and TCAF models were able to spectrally fit the data for acceptable $\chi^2/DOF$. However, for the first 3 epochs, we needed an additional component to fit spectra for acceptable $\chi^2/DOF$. From our analysis, we reported about the possible presence of another component during these first 3 epochs when the source was in the high soft state. This additional component in this state is best described by the bulk motion Comptonization phenomenon. From the TCAF model fitting, we estimated the average mass of the source as $8.1^{+1.3}_{-2.7}~M_\odot$.

Authors:Sharon Mitrani, Ehud Behar

Abstract: The population of meta-stable levels is key to high precision density diagnostics of astrophysical plasmas. In photo-ionized plasmas, density is used to infer the distance from the ionizing source, which is otherwise difficult to obtain. Perfecting models that compute these populations is thus crucial. The present paper presents a semi-analytic hydrogenic approximation for assessing the relative importance of different processes in populating atomic levels. This approximation shows that in the presence of a radiation source, photo- and collisional- excitations are both important over a wide range of plasma temperatures and ionizing spectra, while radiative recombination is orders of magnitude weaker. The interesting case of Fe$^{+21}$ with a collisional radiative model with photo-excitation demonstrates this effect. The population of the first excited meta-stable level in Fe$^{+21}$ is sensitive to the electron number density in the critical range of $n_e=10^{12}-10^{15}\,\rm{cm}^{-3}$; it was observed to be significantly populated in the X-ray spectrum of the 2005 outburst of the X-ray binary GROJ1655-40. The present model shows that photo-excitation is the predominant process indirectly populating the meta-stable level. For the photo-ionized plasma in the GROJ1655-40 outflow, the model indicates a measured value of $n_e=(2.6 \pm 0.5)\times10^{13}\,\rm{cm}^{-3}$ implying a distance from the source of $r=(4.4 \pm 0.4)\times10^{10}$\,cm. Finally, we show how the computed critical density and distance of Fe$^{+21}$ yield the correct ionization parameter of the ion, independent of ionization balance calculations.

Authors:Anirban Dutta, Vikram Rana, Koji Mukai, Raimundo Lopes de Oliveira

Abstract: We present a broadband X-ray study ($\sim$\,0.3-50 keV) of the dwarf nova SS Cyg highlighting the changes in the accretion during two phases, the quiescence and the outburst states. The investigation was based on simultaneous observations carried out with the XMM-Newton and NuSTAR telescopes in two epochs, involving medium and high-resolution spectroscopy. Spectra were harder during quiescence ($kT_{\rm high}\sim22.8$ keV) than outburst ($kT_{\rm high}\sim8.4$ keV), while the mass accretion rate increased by $\sim35$ times in outburst ($1.7\times10^{16} \rm g\;s^{-1}$) than quiescence. The bolometric luminosity (0.01-100.0 keV) during the outburst was dominated by a blackbody emission ($kT_{\rm BB}\sim28$ eV) from the optically thick boundary layer, and the inner edge of the accretion disk resides very close to the WD surface. X-rays from the accretion disk boundary layer are consistent with the white dwarf having mass $1.18_{-0.01}^{+0.02} \rm M_{\odot}$. Our study conclusively confirms the presence of the reflection hump in the 10-30 keV range for both phases, which arises when X-ray photons hit colder material and undergo Compton scattering. We estimated a similarly strong reflection amplitude during quiescence ($\sim1.25$) and outburst ($\sim1.31$), indicating both the WD surface and disk are contributing to reflection. The neutral Fe K$_{\alpha}$ line, which is correlated with Compton reflection, also showed similar strength ($\sim80$ eV) in both phases. Finally, X-rays also revealed the presence of a partial intrinsic absorber during the outburst, possibly due to an outflowing accretion disk wind.

Authors:Antonio Condorelli, Jonathan Biteau, Remi Adam

Abstract: Galaxy clusters are the universe's largest objects in the universe kept together by gravity. Most of their baryonic content is made of a magnetized diffuse plasma. We investigate the impact of such magnetized environment on ultra-high-energy-cosmic-ray (UHECR) propagation. The intracluster medium is described according to the self-similar assumption, in which the gas density and pressure profiles are fully determined by the cluster mass and redshift. The magnetic field is scaled to the thermal components of the intracluster medium under different assumptions. We model the propagation of UHECRs in the intracluster medium using a modified version of the Monte Carlo code {\it SimProp}, where hadronic processes and diffusion in the turbulent magnetic field are implemented. We provide a universal parametrization that approximates the UHECR fluxes escaping from the environment as a function of the most relevant quantities, such as the mass of the cluster, the position of the source with respect to the center of the cluster and the nature of the accelerated particles. We show that galaxy clusters are an opaque environment especially for UHECR nuclei. The role of the most massive nearby clusters in the context of the emerging UHECR astronomy is finally discussed.

Authors:Jujia Zhang, Han Lin, Xiaofeng Wang, Zeyi Zhao, Liping Li, Jialian Liu, Shenyu Yan, Danfeng Xiang, Huijuan Wang, Jinming Bai

Abstract: Type II supernovae represent the most common stellar explosions in the Universe, for which the final stage evolution of their hydrogen-rich massive progenitors towards core-collapse explosion are elusive. The recent explosion of SN 2023ixf in a very nearby galaxy, Messier 101, provides a rare opportunity to explore this longstanding issue. With the timely high-cadence flash spectra taken within 1-5 days after the explosion, we can put stringent constraints on the properties of the surrounding circumstellar material around this supernova. Based on the rapid fading of the narrow emission lines and luminosity/profile of $\rm H\alpha$ emission at very early times, we estimate that the progenitor of SN 2023ixf lost material at a mass-loss rate $\dot{\rm M} \approx 6 \times 10^{-4}\, \rm M_{\odot}\,yr^{-1}$ over the last 2-3 years before explosion. This close-by material, moving at a velocity $v_{\rm w} \approx 55\rm \, km\,s^{-1}$, accumulates a compact CSM shell at the radius smaller than $7 \times 10^{14}$ cm from the progenitor. Given the high mass-loss rate and relatively large wind velocity presented here, together with the pre-explosion observations made about two decades ago, the progenitor of SN 2023ixf could be a short-lived yellow hypergiant that evolved from a red supergiant shortly before the explosion.

Authors:Sho Fujibayashi, Alan Tsz-Lok Lam, Masaru Shibata, Yuichiro Sekiguchi

Abstract: We perform a new general-relativistic viscous-radiation hydrodynamics simulation for supernova-like explosion associated with stellar core collapse of rotating massive stars to a system of a black hole and a massive torus paying particular attention to large-mass progenitor stars with the zero-age main-sequence mass of $M_\mathrm{ZAMS}=$20, 35, and 45$M_\odot$ of Ref.~\cite{Aguilera-Dena2020oct}. Assuming that a black hole is formed in a short timescale after the onset of the stellar collapse, the new simulations are started from initial data of a spinning black hole and infalling matter that self-consistently satisfy the constraint equations of general relativity. It is found that with a reasonable size of the viscous parameter, the supernova-like explosion is driven by the viscous heating effect in the torus around the black hole irrespective of the progenitor mass. The typical explosion energy and ejecta mass for the large-mass cases ($M_\mathrm{ZAMS}=35$ and $45M_\odot$) are $\sim 10^{52}$ erg and $\sim 5M_\odot$, respectively, with $^{56}$Ni mass larger than $0.15M_\odot$. These are consistent with the observational data of stripped-envelope and high-energy supernovae such as broad-lined type Ic supernovae. This indicates that rotating stellar collapses of massive stars to a black hole surrounded by a massive torus can be a central engine for high-energy supernovae. By artificially varying the angular velocity of the initial data, we explore the dependence of the explosion energy and ejecta mass on the initial angular momentum and find that the large explosion energy $\sim 10^{52}$ erg and large $^{56}$Ni mass $\geq 0.15M_\odot$ are possible only when a large-mass compact torus with mass $\gtrsim 1M_\odot$ is formed.

Authors:Lin-Qing Gao, Xiao-Jun Bi, Jun-Guang Guo, Wenbin Lin, Peng-Fei Yin

Abstract: Axion-like particles (ALPs) could mix with photons in the presence of astrophysical magnetic fields, and result in oscillations in the high energy $\gamma$-ray spectra observed by experiments. In this work, we investigate the ALP-photon oscillation effect through the blazar Mrk 421 spectra of 15 periods observed by Major Atmospheric Gamma Imaging Cherenkov Telescopes (MAGIC) and Fermi Large Area Telescope (Fermi-LAT). Compared with previous studies, we generate the mock data under the ALP hypothesis and apply the ${\rm CL_s}$ method to set constraints on the ALP parameters. This method is widely employed in high energy experiments and could avoid the possibility of excluding some parameter regions due to the fluctuation. We find that the ALP-photon coupling $g_{a\gamma}$ is constrained to be smaller than $\sim 2\times10^{-11}$ GeV$^{-1}$ for ALP mass ranging from $10^{-9}$ eV to $10^{-7}$ eV at a 95\% confidence level. The constraints obtained with the method based on the TS distribution under the null hypothesis, which is adopted in many previous astrophysical ALP studies, are also shown. Our results demonstrate that the joint constraints of all the periods from both methods are consistent. However, the latter method fails to provide constraints for some observation periods, whereas the ${\rm CL_s}$ method remains effective in such cases.

Authors:Valenti Bosch-Ramon

Abstract: Jets of active galactic nuclei are potential accelerators of ultra high-energy cosmic rays. Supernovae can occur inside these jets and contribute to cosmic ray acceleration, particularly of heavy nuclei, but that contribution has been hardly investigated so far. We carried out a first dedicated exploration of the role of supernovae inside extragalactic jets in the production of ultra high-energy cosmic rays. We characterized the energy budget of supernova-jet interactions, and the maximum possible energies of the particles accelerated in those events, likely dominated by heavy nuclei. This allowed us to assess whether these interactions can be potential acceleration sites of ultra high-energy cosmic rays, or at least of their seeds. For that, we estimated the cosmic ray luminosity for different galaxy types, and compared the injection rate of cosmic ray seeds into the jet with that due to galactic cosmic ray entrainment. Since the supernova is fueled for a long time by the luminosity of the jet, the energy of a supernova-jet interaction can be several orders of magnitude greater than that of an isolated supernova. Thus, despite the low rate of supernovae expected to occur in the jet, they could still provide more seeds for accelerating ultra high-energy particles than cosmic ray entrainment from the host galaxy. Moreover, these interactions can create sufficiently efficient accelerators to be a source of cosmic rays with energies $\gtrsim 10$~EeV. Supernova-jet interactions can contribute significantly to the production of ultra high-energy cosmic rays, either directly by accelerating these particles themselves or indirectly by providing pre-accelerated seeds.

Authors:Barbara Olmi

Abstract: Based on the expected population of core collapse supernova remnants and the huge number of detected pulsars in the Galaxy, still representing only a fraction of the real population, pulsar wind nebulae are likely to constitute one of the largest classes of {extended} Galactic sources in many energy bands. For simple evolutionary reasons, the majority of the population is made of evolved systems, whose detection and identification are complicated by their reduced luminosity, the possible lack of X-ray emission (that fades progressively away with the age of the pulsar), and by their modified morphology with respect to young systems. Nevertheless they have gained renewed attention in recent years, following the detection of misaligned X-ray tails protruding from an increasing number of nebulae created by fast moving pulsars, and of extended TeV halos surrounding aged systems. Both these features are clear signs of an efficient escape of particles, with energy close to the maximum acceleration limit of the pulsar. Here we discuss the properties of those evolved systems and what we have understood about the process of particle escape, and the formation of observed features.

Authors:Mainak Mukhopadhyay, Mukul Bhattacharya, Kohta Murase

Abstract: Recent radio observations and coincident neutrino detections suggest that some tidal disruption events (TDEs) exhibit late-time activities, relative to the optical emission peak, and these may be due to delayed outflows launched from the central supermassive black hole. We investigate the possibility that jets launched with a time delay of days to months, interact with a debris that may expand outwards. We discuss the effects of the time delay and expansion velocity on the outcomes of jet breakout and collimation. We find that a jet with an isotropic-equivalent luminosity of $\lesssim 5 \times 10^{45}\,{\rm erg/s}$ is likely to be choked for a delay time of $\sim 3$ months. We also study the observational signatures of such delayed choked jets. The jet-debris interaction preceding the breakout would lead to particle acceleration and the resulting synchrotron emission can be detected by current and near-future radio, optical and X-ray telescopes, and the expanding jet-driven debris could explain late-time radio emission. We discuss high-energy neutrino production in delayed choked jets, and the time delay can significantly alleviate the difficulty of the hidden jet scenario in explaining neutrino coincidences.

Authors:Anna Bobrikova, Vladislav Loktev, Tuomo Salmi, Juri Poutanen

Abstract: Pulse profiles of accreting millisecond pulsars can be used to determine neutron star (NS) parameters, such as their masses and radii, and therefore provide constraints on the equation of state of cold dense matter. Information obtained by the Imaging X-ray Polarimetry Explorer (IXPE) can be used to decipher pulsar inclination and magnetic obliquity, providing ever tighter constraints on other parameters. In this paper, we develop a new emission model for accretion-powered millisecond pulsars based on thermal Comptonization in an accretion shock above the NS surface. The shock structure was approximated by an isothermal plane-parallel slab and the Stokes parameters of the emergent radiation were computed as a function of the zenith angle and energy for different values of the electron temperature, the Thomson optical depth of the slab, and the temperature of the seed blackbody photons. We show that our Compton scattering model leads to a significantly lower polarization degree of the emitted radiation compared to the previously used Thomson scattering model. We computed a large grid of shock models, which can be combined with pulse profile modeling techniques both with and without polarization included. In this work, we used the relativistic rotating vector model for the oblate NS in order to produce the observed Stokes parameters as a function of the pulsar phase. Furthermore, we simulated the data to be produced by IXPE and obtained constraints on model parameters using nested sampling. The developed methods can also be used in the analysis of the data from future satellites, such as the enhanced X-ray Timing and Polarimetry mission.

Authors:Debora Mroczek, M. Coleman Miller, Jacquelyn Noronha-Hostler, Nicolas Yunes

Abstract: Measurements of neutron star masses, radii, and tidal deformability have direct connections to nuclear physics via the equation of state (EoS), which for the cold, catalyzed matter in neutron star cores is commonly represented as the pressure as a function of energy density. Microscopic models with exotic degrees of freedom display nontrivial structure in the speed of sound ($c_s$) in the form of first-order phase transitions and bumps, oscillations, and plateaus in the case of crossovers and higher-order phase transitions. We present a procedure based on Gaussian processes to generate an ensemble of EoSs that include nontrivial features. Using a Bayesian analysis incorporating measurements from X-ray sources, gravitational wave observations, and perturbative QCD results, we show that these features are compatible with current constraints. We investigate the possibility of a global maximum in $c_s$ that occurs within the densities realized in neutron stars -- implying a softening of the EoS and possibly an exotic phase in the core of massive stars -- and find that such a global maximum is consistent with, but not required by, current constraints.

Authors:Yangyang Cai, Samuel E. Gralla, Vasileios Paschalidis

Abstract: As first proposed by Gruzinov, a charged particle moving in strong electromagnetic fields can enter an equilibrium state where the power input from the electric field is balanced by radiative losses. When this occurs, the particle moves at nearly light speed along special directions called the principal null directions (PNDs) of the electromagnetic field. This equilibrium is "Aristotelian" in that the particle velocity, rather than acceleration, is determined by the local electromagnetic field. In paper I of this series, we analytically derived the complete formula for the particle velocity at leading order in its deviation from the PND, starting from the fundamental Landau-Lifshitz (LL) equation governing charged particle motion, and demonstrated agreement with numerical solutions of the LL equation. We also identified five necessary conditions on the field configuration for the equilibrium to occur. In this paper we study the entry into equilibrium using a similar combination of analytical and numerical techniques. We simplify the necessary conditions and provide strong numerical evidence that they are also sufficient for equilibrium to occur. Based on exact and approximate solutions to the LL equation, we identify key timescales and properties of entry into equilibrium and show quantitative agreement with numerical simulations. Part of this analysis shows analytically that the equilibrium is linearly stable and identifies the presence of oscillations during entry, which may have distinctive radiative signatures. Our results provide a solid foundation for using the Aristotelian approximation when modeling relativistic plasmas with strong electromagnetic fields.

Authors:Carmelo Evoli, Ulyana Dupletsa

Abstract: When examining the abundance of elements in the placid interstellar medium, a deep hollow between helium and carbon becomes apparent. Notably, the fragile light nuclei Lithium, Beryllium, and Boron (collectively known as LiBeB) are not formed, with the exception of Li7, during the process of Big Bang nucleosynthesis, nor do they arise as byproducts of stellar lifecycles. In contrast to the majority of elements, these species owe their existence to the most energetic particles in the Universe. Cosmic rays, originating in the most powerful Milky Way's particle accelerators, reach the Earth after traversing tangled and lengthy paths spanning millions of years. During their journey, these primary particles undergo transformations through collisions with interstellar matter. This process, known as spallation, alters their composition and introduces secondary light elements in the cosmic-ray beam. In light of this, the relatively large abundance of LiBeB in the cosmic radiation provides remarkable insights into the mechanisms of particle acceleration, as well as the micro-physics of confinement within galactic magnetic fields. These lecture notes are intended to equip readers with basic knowledge necessary for examining the chemical and isotopic composition, as well as the energy spectra, of cosmic rays, finally fostering a more profound comprehension of the complex high-energy astrophysical processes occurring within our Galaxy.

Authors:Nikolaos D. Kylafis, Pablo Reig

Abstract: The observed correlation between the radio and X-ray fluxes in the hard state of black-hole X-ray binaries (BHXRBs) has been around for more than two decades. It is currently accepted that the hard X-rays in BHXRBs come from Comptonization in the corona and the radio emission from the relativistic jet (Lorentz $\gamma >> 1$), which is a narrow structure of a few $R_g=GM/c^2$ at its base. The relativistic jet and the corona, however, are separate entities with hardly any communication between them, apart from the fact that both are fed from the accreting matter. It is also widely accepted that the accretion flow around black holes in BHXRBs consists of an outer thin disk and an inner hot flow. From this hot inner flow, an outflow emanates in the hard and hard-intermediate states of the source. By considering Compton up-scattering of soft disk photons in the outflow (i.e., in the outflowing corona, which is a wider structure, tens to hundreds of $R_g$ at its base, with low Lorentz gamma) as the mechanism that produces the hard X-ray spectrum, we have been able to explain quantitatively a number of observed correlations. Here, we demonstrate that this outflowing corona can also explain quantitatively the observed radio - X-ray correlation. In addition, we make the following theoretical predictions for GX 339-4: 1) the radio flux in the hard and hard-intermediate states should be a bell-shaped curve as a function of the photon-number spectral index Gamma, 2) the radio - X-ray correlation should break down when the source moves from the hard to the hard-intermediate state and instead the radio flux should first increase sharply in the hard-intermediate state and then decrease also sharply, in a very narrow range of the X-ray flux, and 3) the X-ray polarization will be parallel to the outflow in the hard state and perpendicular to it in the hard-intermediate one.

Authors:Adithiya Dinesh, Gopal Bhatta, Tek P. Adhikari, Maksym Mohorian, Niraj Dhital, Suvas C. Chaudhary, Radim Panis, Dariusz Gora

Abstract: Blazars exhibit relentless variability across diverse spatial and temporal frequencies. The study of long- and short-term variability properties observed in the X-ray band provides insights into the inner workings of the central engine. In this work, we present timing and spectral analyses of the blazar 3C 273 using the X-ray observations from the $\textit{XMM-Newton}$ telescope covering the period from 2000 to 2020. The methods of timing analyses include estimation of fractional variability, long- and short-term flux distribution, rms-flux relation, and power spectral density analysis. The spectral analysis include estimating a model independent flux hardness ratio and fitting the observations with multiplicative and additive spectral models such as \textit{power-law}, \textit{log-parabola}, \textit{broken power-law}, and \textit{black body}. The \textit{black body} represents the thermal emission from the accretion disk, while the other models represent the possible energy distributions of the particles emitting synchrotron radiation in the jet. During the past two decades, the source flux changed by of a factor of three, with a considerable fractional variability of 27\%. However, the intraday variation was found to be moderate. Flux distributions of the individual observations were consistent with a normal or log-normal distribution, while the overall flux distribution including entire observations appear to be rather multi-modal and of a complex shape. The spectral analyses indicate that \textit{log-parabola} added with a \textit{black body} gives the best fit for most of the observations. The results indicate a complex scenario in which the variability can be attributed to the intricate interaction between the disk/corona system and the jet.

Authors:Nicolas De Angelis, J. Michael Burgess, Franck Cadoux, Jochen Greiner, Merlin Kole, Hancheng Li, Slawomir Mianowski, Agnieszka Pollo, Nicolas Produit, Dominik Rybka, Jianchao Sun, Xin Wu, Shuang-Nan Zhang

Abstract: Gamma-Ray Bursts are among the most powerful events in the Universe. Despite half a century of observations of these transient sources, many open questions remain about their nature. Polarization measurements of the GRB prompt emission have long been theorized to be able to answer most of these questions. With the aim of characterizing the polarization of these prompt emissions, a compact Compton polarimeter, called POLAR, has been launched to space in September 2016. Time integrated polarization analysis of the POLAR GRB catalog have shown that the prompt emission is lowly polarized or fully unpolarized. However, time resolved analysis depicted strong hints of an evolving polarization angle within single pulses, washing out the polarization degree in time integrated analyses. Here we will for the first time present energy resolved polarization measurements with the POLAR data. The novel analysis, performed on several GRBs, will provide new insights and alter our understanding of GRB polarization. The analysis was performed using the 3ML framework to fit polarization parameters versus energy in parallel to the spectral parameters. Although limited by statistics, the results could provide a very relevant input to disentangle between existing theoretical models. In order to gather more statistics per GRB and perform joint time and energy resolved analysis, a successor instrument, called POLAR-2, is under development with a launch window early 2025 to the CSS. After presenting the first energy resolved polarization results of the POLAR mission, we will present the prospects for such measurements with the upcoming POLAR-2 mission.

Authors:Travis Court, Carles Badenes, Shiu-Hang Lee, Daniel Patnaude, Guillermo García-Segura, Eduardo Bravo

Abstract: The nature of Type Ia Supernova (SN Ia) explosions remains an open issue, with several contending progenitor scenarios actively being considered. One such scenario involves a SN Ia explosion inside a planetary nebula (PN) in the aftermath of a stellar merger triggered by a common envelope (CE) episode. We examine this scenario using hydrodynamic and non-equilibrium ionization simulations of the interaction between the SN ejecta and the PN cocoon into the supernova remnant (SNR) phase, focusing on the impact of the delay between the CE episode and the SN explosion. We compare the bulk dynamics and X-ray spectra of our simulated SNRs to the observed properties of known Type Ia SNRs in the Milky Way and the Magellanic Clouds. We conclude that models where the SN explosion happens in the immediate aftermath of the CE episode (with a delay $\lesssim$1,000 yr) are hard to reconcile with the observations, because the interaction with the dense PN cocoon results in ionization timescales much higher than those found in any known Type Ia SNR. Models with a longer delay between the CE episode and the SN explosion ($\sim$10,000 yr) are closer to the observations, and may be able to explain the bulk properties of some Type Ia SNRs.

Authors:Sandeep Kumar Mondal, Saikat Das, Nayantara Gupta

Abstract: Markarian (Mrk) 180 is a High frequency-peaked BL Lacertae object or HBL object, located at a redshift of 0.045 and a potential candidate for high-energy cosmic ray acceleration. In this work, we have done a temporal and spectral study using Fermi Large Area Telescope (Fermi-LAT) $\gamma$-ray data, collected over 12.8 years. In the case of the temporal study, the 12.8 years long, 30-day binned, Fermi-LAT $\gamma$-ray light curve does not show any significant enhancement of the flux. To understand the underlying physical mechanism, we focused our study on multi-wavelength spectral analysis. We constructed multi-wavelength spectral energy distribution (MWSED) using Swift X-ray, ultraviolet & optical, and X-ray Multi-Mirror Mission (XMM-Newton) data, which have been analysed thoroughly. The SED has been modelled with three different models: (i) pure leptonic scenario and lepto-hadronic scenario where we considered two types of lepto-hadronic interactions (ii) line-of-sight interactions of ultrahigh-energy cosmic rays (UHECR; $E\gtrsim 10^{17}$ eV) with the cosmic background radiation and (iii) interaction between relativistic protons with the cold proton within the blazar jet. In this literature, we have done a detailed comparative study between all these three models. In an earlier study, Mrk 180 was associated with the Telescope Array (TA) hotspot of UHECRs at $E>57$ EeV which motivates us to check whether Mrk 180 can be a source of UHECRs, contributing to the TA hotspot. From our study, we find, for conservative strengths of the extragalactic magnetic field, Mrk 180 is unlikely to be a source of UHECR events.

Authors:Kevin Almeida Cheminant, Dariusz Gora, Nataliia Borodai, Ralph Engel, Tanguy Pierog, Jan Pekala, Markus Roth, Jarosław Stasielak, Michael Unger, Darko Veberic, Henryk Wilczynski

Abstract: The number of muons in an air shower is a strong indicator of the mass of the primary particle and increases with a small power of the cosmic ray mass by the $\beta$-exponent, $N_{\mu} \sim A^{(1-\beta)}$. This behaviour can be explained in terms of the Heitler-Matthews model of hadronic air showers. In this paper, we present a method for calculating $\beta$ from the Heitler-Matthews model. The method has been successfully verified with a series of simulated events observed by the Pierre Auger Observatory at $10^{19}$ eV. To follow real measurements of the mass composition at this energy, the generated sample consists of a certain fraction of events produced with p, He, N and Fe primary energies. Since hadronic interactions at the highest energies can differ from those observed at energies reached by terrestrial accelerators, we generate a mock data set with $\beta =0.92$ (the canonical value) and $\beta =0.96$ (a more exotic scenario). The method can be applied to measured events to determine the muon signal for each primary particle as well as the muon scaling factor and the $\beta$-exponent. Determining the $\beta$-exponent can effectively constrain the parameters that govern hadronic interactions and help solve the so-called muon problem, where hadronic interaction models predict too few muons relative to observed events. In this paper, we lay the foundation for the future analysis of measured data from the Pierre Auger Observatory with a simulation study.

Authors:A. M. W. Mitchell for the H.E.S.S. collaboration, S. Caroff for the H.E.S.S. collaboration

Abstract: Geminga is an enigmatic radio-quiet gamma-ray pulsar located at a mere 250 pc distance from Earth. Extended very-high-energy gamma-ray emission around the pulsar has been detected by multiple water Cherenkov detector based instruments. However, the detection of extended TeV gamma-ray emission around the Geminga pulsar has proven challenging for IACTs due to the angular scale exceeding the typical field-of-view. By detailed studies of background estimation techniques and characterising systematic effects, a detection of highly extended TeV gamma-ray emission could be confirmed by the H.E.S.S. IACT array. Building on the previously announced detection, in this contribution we further characterise the emission and apply an electron diffusion model to the combined gamma-ray data from the H.E.S.S. and HAWC experiments, as well as X-ray data from XMM-Newton.

Authors:Felix Aharonian, Denys Malyshev, Maria Chernyakova

Abstract: HESS J1702-420 is a multi-TeV gamma-ray source with an unusual energy-dependent morphology. The recent H.E.S.S. observations suggest that the emission is well described by a combination of point-like HESS J1702-420A (dominating at highest energies, $\gtrsim$ 30 TeV ) and diffuse ($\sim$ 0.3$^\circ$) HESS J1702-420B (dominating below $\lesssim$ 5TeV) sources with very hard (${\Gamma} \sim 1.5$) and soft (${\Gamma}$ ~2.6) power-law spectra, respectively. Here we propose a model which postulates that the proton accelerator is located at the position of HESS J1702-420A and is embedded into a dense molecular cloud that coincides with HESS J1702-420B. In the proposed model, the VHE radiation of HESS J1702-420 is explained by the pion-decay emission from the continuously injected relativistic protons propagating through a dense cloud. The energy-dependent morphology is defined by the diffusive nature of the low-energy protons propagation, transiting sharply to (quasi) ballistic propagation at higher energies. Adopting strong energy dependence of the diffusion coefficient, $D \propto E^\beta$ with $\beta \geq 1$, we argue that HESS J1702-420 as the system of two gamma-ray sources is the result of the propagation effect. Protons injected by a single accelerator at the rate $Q_0 \simeq 10^{38} \, (n_0/100 \, \rm cm^{-3})^{-1}\, (d/ \, 0.25\,kpc)^{-1} \rm erg/s$ can reasonably reproduce the morphology and fluxes of two gamma-ray components.

Authors:Federica Bradascio for the H.E.S.S. and IceCube Collaborations, Halim Ashkar for the H.E.S.S. and IceCube Collaborations, Jowita Borowska for the H.E.S.S. and IceCube Collaborations, Jean Damascene Mbarubucyeye for the H.E.S.S. and IceCube Collaborations, Enzo Oukacha for the H.E.S.S. and IceCube Collaborations, Fabian Schüssler for the H.E.S.S. and IceCube Collaborations, Hiromasa Suzuki for the H.E.S.S. and IceCube Collaborations, Alicja Wierzcholska for the H.E.S.S. and IceCube Collaborations

Abstract: The evidence for multi-messenger photon and neutrino emission from the blazar TXS 0506+056 has demonstrated the importance of realtime follow-up of neutrino events by various ground- and space-based facilities. The effort of H.E.S.S. and other experiments in coordinating observations to obtain quasi-simultaneous multiwavelength flux and spectrum measurements has been critical in measuring the chance coincidence with the high-energy neutrino event IC-170922A and constraining theoretical models. For about a decade, the H.E.S.S. transient program has included a search for gamma-ray emission associated with high-energy neutrino alerts, looking for gamma-ray activity from known sources and newly detected emitters consistent with the neutrino location. In this contribution, we present an overview of follow-up activities for realtime neutrino alerts with H.E.S.S. in 2021 and 2022. Our analysis includes both public IceCube neutrino alerts and alerts exchanged as part of a joint H.E.S.S.-IceCube program. We focus on interesting coincidences observed with gamma-ray sources, particularly highlighting the significant detection of PKS 0625-35, an AGN previously detected by H.E.S.S., and three IceCube neutrinos.

Authors:T. Wach for the H.E.S.S. collaboration, A. M. W. Mitchell for the H.E.S.S. collaboration, V. Joshi for the H.E.S.S. collaboration, S. Funk for the H.E.S.S. collaboration

Abstract: HESS J1813-178 is one of the brightest sources detected during the first HESS Galactic Plane survey. The compact source, also detected by MAGIC, is believed to be a pulsar wind nebula powered by one of the most powerful pulsars known in the Galaxy, PSR J1813-1749 with a spin-down luminosity of $\dot{\mathrm{E}} = 5.6 \cdot 10^{37}\,\mathrm{erg}\,\mathrm{s}^{-1}$. With its extreme physical properties, as well as the pulsar's young age of 5.6 kyrs, the $\gamma$-rays detected in this region allow us to study the evolution of a highly atypical system. Previous studies of the region in the GeV energy range show emission extended beyond the size of the compact H.E.S.S. source. Using the archival H.E.S.S. data with improved background methods, we perform a detailed morphological and spectral analysis of the region. Additionally to the compact, bright emission component, we find significantly extended emission, whose position is coincident with HESS J1813-178. We reanalyse the region in GeV and derive a joint-model in order to find a continuous description of the emission in the region from GeV to TeV. Using the results derived in this analysis, as well as X-ray and radio data of the region, we perform multi-wavelength spectral modeling. Possible hadronic or leptonic origins of the $\gamma$-ray emission are investigated, and the diffusion parameters necessary to explain the extended emission are examined.

Authors:Mahdi Najafi-Ziyazi, Jordy Davelaar, Yosuke Mizuno, Oliver Porth

Abstract: Recent polarimetric mm-observations of the galactic centre by Wielgus et al. (2022a) showed sinusoidal loops in the Q-U plane with a duration of one hour. The loops coincide with a quasi-simultaneous X-ray flare. A promising mechanism to explain the flaring events are magnetic flux eruptions in magnetically arrested accretion flows (MAD). In our previous work (Porth et al. 2021), we studied the accretion flow dynamics during flux eruptions. Here, we extend our previous study by investigating whether polarization loops can be a signature produced by magnetic flux eruptions. We find that loops in the Q-U plane are robustly produced in MAD models as they lead to enhanced emissivity of compressed disk material due to orbiting flux bundles. A timing analysis of the synthetic polarized lightcurves demonstrate a polarized excess variability at timescales of ~ 1 hr. The polarization loops are also clearly imprinted on the cross-correlation of the Stokes parameters which allows to extract a typical periodicity of 30 min to 1 hr with some evidence for a spin dependence. These results are intrinsic to the MAD state and should thus hold for a wide range of astrophysical objects. A subset of GRMHD simulations without saturated magnetic flux (single temperature SANE models) also produces Q-U loops. However, in disagreement with the findings of Wielgus et al. (2022a), loops in these simulations are quasi-continuous with a low polarization excess

Authors:Ji-Gui Cheng, Yun-Feng Liang, En-Wei Liang

Abstract: Weakly interacting massive particles, as a major candidate of dark matter (DM), may directly annihilate or decay into high-energy photons, producing monochromatic spectral lines in the gamma-ray band. These spectral lines, if detected, are smoking-gun signatures for the existence of new physics. Using the 5 years of DAMPE and 13 years of Fermi-LAT data, we search for line-like signals in the energy range of 3 GeV to 1 TeV from the Galactic halo. Different regions of interest are considered to accommodate different DM density profiles. We do not find any significant line structure, and the previously reported line-like feature at $\sim$133 GeV is also not detected in our analysis. Adopting a local DM density of $\rho_{\rm local}=0.4\,{\rm GeV\,cm^{-3}}$, we derive 95% confidence level constraints on the velocity-averaged cross-section of $\langle{\sigma v}\rangle_{\gamma\gamma} \lesssim 4 \times 10^{-28}\,{\rm cm^{3}\,s^{-1}}$ and the decay lifetime of $\tau_{\gamma\nu} \gtrsim 5 \times 10^{29}\,{\rm s}$ at 100 GeV, achieving the strongest constraints to date for the line energies of 6-660 GeV. The improvement stems from the longer Fermi-LAT data set used and the inclusion of DAMPE data in the analysis. The simultaneous use of two independent data sets could also reduce the systematic uncertainty of the search.

Authors:Zheng Cao, Lie-Wen Chen

Abstract: Neutron stars (NSs) which could contain exotic degrees of freedom in the core and the self-bound quark stars (QSs) made purely of absolutely stable deconfined quark matter are still two main candidates for the compact objects observed in pulsars and gravitational wave (GW) events in binary star mergers. We perform a Bayesian model-agnostic inference of the properties of NSs and QSs by combining multi-messenger data of GW170817, GW190425, PSR J0030+0451, PSR J0740+6620, PSR J1614-2230, PSR J0348+0432 as well as ab initio calculations from perturbative quantum chromodynamics and chiral effective field theory. We find the NS scenario is strongly favored against the QS scenario with a Bayes factor of NS over QS $\mathcal{B}^\text{NS}_\text{QS} = 11.5$. In addition, the peak of the squared sound velocity $c_s^2 \sim 0.5c^2$ around $3.5$ times nuclear saturation density $n_0$ observed in the NS case disappears in the QS case which suggests that the $c_s^2$ first increases and then saturates at $c_s^2 \sim 0.5c^2$ above $\sim 4n_0$. The sound velocity and trace anomaly are found to approach the conformal limit in the core of heavy NSs with mass $M \gtrsim 2M_{\odot}$, but not in the core of QSs.

Authors:Nicholas Vieira, John J. Ruan, Daryl Haggard, Nicole M. Ford, Maria R. Drout, Rodrigo Fernández

Abstract: In kilonovae, freshly-synthesized $r$-process elements imprint features on optical spectra, as observed in AT2017gfo, the counterpart to the GW170817 binary neutron star merger. However, measuring the $r$-process compositions of the merger ejecta is computationally challenging. Vieira et al. (2023) introduced Spectroscopic $r$-Process Abundance Retrieval for Kilonovae (SPARK), a software tool to infer elemental abundance patterns of the ejecta, and associate spectral features with particular species. Previously, we applied SPARK to the 1.4 day spectrum of AT2017gfo and inferred its abundance pattern for the first time, characterized by electron fraction $Y_e=0.31$, a substantial abundance of strontium, and a dearth of lanthanides and heavier elements. This ejecta is consistent with wind from a remnant hypermassive neutron star and/or accretion disk. We now extend our inference to spectra at 2.4 and 3.4 days, and test the need for multi-component ejecta, where we stratify the ejecta in composition. The ejecta at 1.4 and 2.4 days is described by the same single blue component. At 3.4 days, a new redder component with lower $Y_e=0.16$ and a significant abundance of lanthanides emerges. This new redder component is consistent with dynamical ejecta and/or neutron-rich ejecta from a magnetized accretion disk. As expected from photometric modelling, this component emerges as the ejecta expands, the photosphere recedes, and the earlier bluer component dims. At 3.4 days, we find an ensemble of lanthanides, with the presence of cerium most concrete. This presence of lanthanides has important implications for the contribution of kilonovae to the $r$-process abundances observed in the Universe.

Authors:M. Colom i Bernadich, V. Balakrishnan, E. Barr, M. Berezina, M. Burgay, S. Buchner, D. J. Champion, G. Desvignes, P. C. C. Freire, K. Grunthal, M. Kramer, Y. Men, P. V. Padmanabh, A. Parthasarathy, D. Pillay, I. Rammala, S. Sengupta, V. Venkatraman Krishnan

Abstract: The MMGPS-L is the most sensitive pulsar survey in the Southern Hemisphere. We present a follow-up study of one of these new discoveries, PSR J1208-5936, a 28.71-ms recycled pulsar in a double neutron star system with an orbital period of Pb=0.632 days and an eccentricity of e=0.348. Through timing of almost one year of observations, we detected the relativistic advance of periastron (0.918(1) deg/yr), resulting in a total system mass of Mt=2.586(5) Mo. We also achieved low-significance constraints on the amplitude of the Einstein delay and Shapiro delay, in turn yielding constraints on the pulsar mass (Mp=1.26(+0.13/-0.25) Mo), the companion mass (Mc=1.32(+0.25/-0.13) Mo, and the inclination angle (i=57(2) degrees). This system is highly eccentric compared to other Galactic field double neutron stars with similar periods, possibly hinting at a larger-than-usual supernova kick during the formation of the second-born neutron star. The binary will merge within 7.2(2) Gyr due to the emission of gravitational waves. With the improved sensitivity of the MMGPS-L, we updated the Milky Way neutron star merger rate to be 25(+19/-9) Myr$^{-1}$ within 90% credible intervals, which is lower than previous studies based on known Galactic binaries owing to the lack of further detections despite the highly sensitive nature of the survey. This implies a local cosmic neutron star merger rate of 293(+222/-103} Gpc/yr, consistent with LIGO and Virgo O3 observations. With this, we predict the observation of 10(+8/-4) neutron star merger events during the LIGO-Virgo-KAGRA O4 run. We predict the uncertainties on the component masses and the inclination angle will be reduced to 5x10$^{-3}$ Mo and 0.4 degrees after two decades of timing, and that in at least a decade from now the detection of the shift in Pb and the sky proper motion will serve to make an independent constraint of the distance to the system.

Authors:Ivan Z. Stefanov

Abstract: The aim of the current paper is to apply the method of Bambi (Bambi, 2015) to a source which contains two or more simultaneous triads of variability components. The joint chi-square variable that can be composed in this case, unlike some previous studies, allows the goodness of the fit to be tested. It appears that a good fit requires one of the observation groups to be disregarded. Even then, the model prediction for the mass of the neutron star in the accreting millisecond pulsar IGR J17511-3057 is way too high to be accepted.

Authors:S. Prabu, J. C. A. Miller-Jones, A. Bahramian, C. M. Wood, S. J. Tingay, P. Atri, R. M. Plotkin, J. Strader

Abstract: Using multi-frequency Very Long Baseline Interferometer (VLBI) observations, we probe the jet size in the optically thick hard state jets of two black hole X-ray binary (BHXRB) systems, MAXI J1820+070 and V404 Cygni. Due to optical depth effects, the phase referenced VLBI core positions move along the jet axis of the BHXRB in a frequency dependent manner. We use this "core shift" to constrain the physical size of the hard state jet. We place an upper limit of $0.3$\,au on the jet size measured between the 15 and 5 GHz emission regions of the jet in MAXI J1820+070, and an upper limit of $1.0$\,au between the $8.4$ and $4.8$\,GHz emission regions of V404 Cygni. Our limit on the jet size in MAXI J1820+070 observed in the low-hard state is a factor of $5$ smaller than the values previously observed in the high-luminosity hard state (using time lags between multi-frequency light curves), thus showing evidence of the BHXRB jet scaling in size with jet luminosity. We also investigate whether motion of the radio-emitting region along the jet axis could affect the measured VLBI parallaxes for the two systems, leading to a mild tension with the parallax measurements of Gaia. Having mitigated the impact of any motion along the jet axis in the measured astrometry, we find the previous VLBI parallax measurements of MAXI J1820+070 and V404 Cygni to be unaffected by jet motion. With a total time baseline of $8$ years, due to having incorporated fourteen new epochs in addition to the previously published ones, our updated parallax measurement of V404 Cygni is $0.450 \pm 0.018$\,mas ($2.226 \pm 0.091$\,kpc).

Authors:Chul Min Kim, Sang Pyo Kim

Abstract: Highly magnetized neutron stars have magnetic fields of order of the critical field and can lead to measurable QED effects. We consider the Goldreich-Julian pulsar model with supercritical magnetic fields, induced subcritical electric fields, and a period of milliseconds. We then study the strong field physics, such as Schwinger pair production and the vacuum birefringence including the wrench effect, whose X-ray polarimetry will be observed in future space missions.

Authors:Shihong Zhan, Wei Wang

Abstract: As one of the brightest galactic ${\gamma}$-ray sources, the Cygnus Cocoon superbubble has been observed by many detectors, such as $Fermi$-LAT, ARGO, HAWC, and LHAASO. However, the origin of $\gamma$-ray emission for the Cygnus Cocoon and the possible contribution to PeV cosmic rays are still under debate. The recent ultrahigh-energy $\gamma$-ray observations by LHAASO up to 1.4 PeV towards the direction of the Cygnus Cocoon, as well as the neutrino event report of IceCube-201120A coming from the same direction, suggest that the Cygnus Cocoon may be one of the sources of high-energy cosmic rays in the Galaxy. In this work, we propose a dual-zone diffusion model for the Cygnus Cocoon: the cocoon region and surrounding interstellar medium (ISM). This scenario can account for the $\gamma$-ray data from GeV to $\sim$ 50 TeV and agree with the one sub-PeV neutrino event result from IceCube so far. Moreover, it predict a non-negligible contribution $\gamma$-ray emission at hundreds TeV from the ISM surrounding the Cygnus Cocoon. This possible diffuse TeV-PeV gamma-ray features can be resolved by the future LHAASO observations.

Authors:Gabriel Torralba Paz, Artem Bohdan, Jacek Niemiec

Abstract: Acceleration processes that occur in astrophysical plasmas produce cosmic rays that are observed on Earth. To study particle acceleration, fully-kinetic particle-in-cell (PIC) simulations are often used as they can unveil the microphysics of energization processes. Tracing of individual particles in PIC simulations is particularly useful in this regard. However, by-eye inspection of particle trajectories includes a high level of bias and uncertainty in pinpointing specific acceleration mechanisms that affect particles. Here we present a new approach that uses neural networks to aid individual particle data analysis. We demonstrate this approach on the test data that consists of 252,000 electrons which have been traced in a PIC simulation of a non-relativistic high Mach number perpendicular shock, in which we observe the two-stream electrostatic Buneman instability to pre-accelerate a portion of electrons to nonthermal energies. We perform classification, regression and anomaly detection by using a Convolutional Neural Network. We show that regardless of how noisy and imbalanced the datasets are, the regression and classification are able to predict the final energies of particles with high accuracy, whereas anomaly detection is able to discern between energetic and non-energetic particles. The methodology proposed may considerably simplify particle classification in large-scale PIC and also hybrid kinetic simulations.

Authors:Yu-Hua Yao, Xu-Lin Dong, Yi-Qing Guo, Qiang Yuan

Abstract: Recent observations of cosmic rays (CRs) have revealed a two-component anomaly in the spectra of primary and secondary particles, as well as their ratios, prompting investigation into their common origin. In this study, we incorporate the identification of slow diffusion zones around sources as a common phenomenon into our calculations, which successfully reproduces all previously described anomalies except for the positron spectrum. Crucially, our research offers a clear physical picture of the origin of CR: while high-energy ($\textrm{>200~GV}$, including the knee) particles are primarily produced by fresh accelerators and are confined to local regions, low energy ($\textrm{<200~GV}$) components come from distant sources and travel through the outer diffusive zone outside of the galactic disk. This scenario can be universally applied in the galactic disk, as evidenced by ultra-high energy diffuse $\rm\gamma$-ray emissions detected by the AS$\rm\gamma$ experiment. Furthermore, our results predict that the spectrum of diffuse $\rm\gamma$-ray is spatial-dependent, resting with local sources, which can be tested by LHAASO experiment.

Authors:Emanuele Greco, Jacco Vink, Amael Ellien, Carlo Ferrigno

Abstract: Synchrotron radiation from relativistic electrons is usually invoked as the responsible for the nonthermal emission observed in Supernova Remnants (SNRs). Diffusive shock acceleration (DSA) is the most popular mechanism to explain the process of particles acceleration and within its framework a crucial role is played by the turbulent magnetic-field. However, the standard models commonly used to fit X-ray synchrotron emission do not take into account the effects of turbulence in the shape of the resulting photon spectra. An alternative mechanism that properly includes such effects is the jitter radiation, that provides for an additional power-law beyond the classical synchrotron cutoff. We fitted a jitter spectral model to Chandra, NuSTAR, SWIFT/BAT and INTEGRAL/ISGRI spectra of Cassiopeia A and found that it describes the X-ray soft-to-hard range better than any of the standard cutoff models. The jitter radiation allows us to measure the index of the magnetic turbulence spectrum $\nu_B$ and the minimum scale of the turbulence $\lambda_{\rm{min}}$ across several regions of Cas A, with best-fit values $\nu_B \sim 2-2.4$ and $\lambda_{\rm{min}} \lesssim 100$ km.

Authors:Fatemeh Kayanikhoo, Miljenko Cemeljic, Maciek Wielgus, Wlodek Kluzniak

Abstract: During substructure formation in magnetized astrophysical plasma, dissipation of magnetic energy facilitated by magnetic reconnection affects the system dynamics by heating and accelerating the ejected plasmoids. Numerical simulations are a crucial tool for investigating such systems. In astrophysical simulations, the energy dissipation, reconnection rate and substructure formation critically depend on the onset of reconnection of numerical or physical origin. In this paper, we hope to assess the reliability of the state-of-the-art numerical codes, PLUTO and KORAL by quantifying and discussing the impact of dimensionality, resolution, and code accuracy on magnetic energy dissipation, reconnection rate, and substructure formation. We quantitatively compare results obtained with relativistic and non-relativistic, resistive and non-resistive, as well as two- and three-dimensional setups performing the Orszag-Tang test problem. We find the sufficient resolution in each model, for which numerical error is negligible and the resolution does not significantly affect the magnetic energy dissipation and reconnection rate. The non-relativistic simulations show that at sufficient resolution, magnetic and kinetic energies convert to internal energy and heat up the plasma. The results show that in the relativistic system, energy components undergo mutual conversion during the simulation time, which leads to a substantial increase in magnetic energy at 20\% and 90\% of the total simulation time of $10$ light-crossing times -- the magnetic field is amplified by a factor of five due to relativistic shocks. We also show that the reconnection rate in all our simulations is higher than $0.1$, indicating plasmoid-mediated regime. It is shown that in KORAL simulations magnetic energy is slightly larger and more substructures are captured than in PLUTO simulations.

Authors:Motoko Fujiwara, Koichi Hamaguchi, Natsumi Nagata, Maura E. Ramirez-Quezada

Abstract: Recent observations of old warm neutron stars suggest the presence of a heating source in these stars, requiring a paradigm beyond the standard neutron-star cooling theory. In this work, we study the scenario where this heating is caused by the friction associated with the creep motion of neutron superfluid vortex lines in the crust. As it turns out, the heating luminosity in this scenario is proportional to the time derivative of the angular velocity of the pulsar rotation, and the proportional constant $J$ has an approximately universal value for all neutron stars. This $J$ parameter can be determined from the temperature observation of old neutron stars because the heating luminosity is balanced with the photon emission at late times. We study the latest data of neutron star temperature observation and find that these data indeed give similar values of $J$, in favor of the assumption that the frictional motion of vortex lines heats these neutron stars. These values turn out to be consistent with the theoretical calculations of the vortex-nuclear interaction.

Authors:A. Hennessy, R. L. C. Starling, A. Rowlinson, I. de Ruiter, A. Kumar, R. A. J. Eyles-Ferris, A. K. Ror, G. E. Anderson, K. Gourdji, A. J. van der Horst, S. B. Pandey, T. W. Shimwell, D. Steeghs, N. Stylianou, S. ter Veen, K. Wiersema, R. A. M. J. Wijers

Abstract: The composition of relativistic gamma-ray burst (GRB) jets and their emission mechanisms are still debated, and they could be matter or magnetically dominated. One way to distinguish these mechanisms arises because a Poynting flux dominated jet may produce low-frequency radio emission during the energetic prompt phase, through magnetic reconnection at the shock front. We present a search for radio emission coincident with three GRB X-ray flares with the LOw Frequency ARray (LOFAR), in a rapid response mode follow-up of long GRB 210112A (at z~2) with a 2 hour duration, where our observations began 511 seconds after the initial swift-BAT trigger. Using timesliced imaging at 120-168 MHz, we obtain upper limits at 3 sigma confidence of 42 mJy averaging over 320 second snapshot images, and 87 mJy averaging over 60 second snapshot images. LOFAR's fast response time means that all three potential radio counterparts to X-ray flares are observable after accounting for dispersion at the estimated source redshift. Furthermore, the radio pulse in the magnetic wind model was expected to be detectable at our observing frequency and flux density limits which allows us to disfavour a region of parameter space for this GRB. However, we note that stricter constraints on redshift and the fraction of energy in the magnetic field are required to further test jet characteristics across the GRB population.

Authors:Yi-Fan Wang, Alexander H. Nitz

Abstract: Searches for gravitational waves from compact-binary mergers, which to date have reported nearly 100 observations, have previously ignored binaries whose components are both light ($< 2 M_\odot$) and have high dimensionless spin ($>$ 0.05). While previous searches targeted sources that are representative of observed double neutron star binaries in the galaxy, it is already known that neutron stars can regularly be spun up to a dimensionless spin of $\sim$ 0.4, and in principle reach up to $\sim$ 0.7 before breakup would occur. Furthermore, there may be primordial black hole binaries or exotic formation mechanisms to produce subsolar mass black holes. In these cases, it is possible for the binary constituent to be spun up beyond that achievable by a neutron star. A single detection of this type of source would reveal a novel formation channel for compact binaries. To determine if there is evidence for any such sources, we conduct the first search of LIGO and Virgo data from three observing runs for light compact objects with high spin. Our analysis detects previously known observations e.g. GW170817 and GW200115; however, we report no additional mergers. The most significant candidate, not previously known, is consistent with the noise distribution, and so we constrain the merger rate of spinning light binaries.

Authors:Hemanth Manikantan, Biswajit Paul, Vikram Rana

Abstract: Some of the accreting X-ray pulsars are reported to exhibit a peculiar spectral feature at $\sim$10 keV, known as the "10 keV feature". The feature has been characterized as either an emission line or an absorption line, and its origin is unknown. It has been found in multiple observations of the same source by different observatories, but not all the observations of any particular source consistently showed the presence of it. In this work, we have carried out a systematic investigation for the presence of the "10 keV feature" using data from NuSTAR, a low background spectroscopic observatory having uninterrupted wide band coverage on either side of 10 keV. We performed a systematic spectral analysis on 58 archival NuSTAR observations of 30 bright X-ray pulsars. The 3$-$79 keV spectral continua of these selected sources were fitted with a model chosen on the basis of its fitting quality in 3$-$15 keV and model simplicity, and then inspected for the presence of the "10 keV feature". Our analysis indicates the presence of such a feature in 16 out of 58 the NuSTAR observations of 11 different sources and is fitted with a Gaussian absorption model centered around 10 keV. Our analysis also suggests that such a feature could be wrongly detected if flare data is not analyzed separately from persistent emission.

Authors:Vladislav Loktev, Alexandra Veledina, Juri Poutanen, Joonas Nättilä, Valery F. Suleimanov

Abstract: Spectro-polarimetric signatures of accretion disks in X-ray binaries and active galactic nuclei contain information about the masses and spins of their central black holes, as well as the geometry of matter close to the compact objects. This information can be extracted using the means of X-ray polarimetry. In this work, we present a fast analytical ray-tracing technique for polarized light \textsc{artpol} that helps obtain the spinning black hole parameters from the observed properties. This technique can replace the otherwise time-consuming numerical ray-tracing calculations. We show that \textsc{artpol} proves accurate for Kerr black holes with dimensionless spin parameter $a\leq0.94$ while being over four orders of magnitude faster than direct ray-tracing calculations. This approach opens broad prospects for directly fitting the spectro-polarimetric data from the \textit{Imaging X-ray Polarimetry Explorer}.

Authors:Neha Lad for the IceCube Collaboration, D. F. Cowen for the IceCube Collaboration

Abstract: We present a summary of the flavor composition measurements for the diffuse astrophysical neutrino flux using data from the IceCube Neutrino Observatory at the South Pole. IceCube has identified candidate astrophysical tau neutrinos through two different approaches. One approach used a dedicated particle identification algorithm for the classification and reconstruction of the 'Double Cascade' event topology, a signature of tau neutrino charged current interactions. This first approach is applied to the High Energy Starting Events (HESE) sample, an all-sky, all-flavor set of neutrino events with energy above 60~TeV encompassing 12 years of IceCube livetime. We show that the addition of more years of data and updated ice properties on the HESE sample delivers tighter constraints on the flavor composition of the astrophysical neutrino flux than previous IceCube analyses, in particular when it is fit in combination with high statistics samples of through-going tracks and cascades. A second approach uses a sensitive machine-learning-based selection technique that finds seven candidate events in 9.7 years of IceCube data. This approach excludes the zero astrophysical tau neutrino hypothesis at the highest statistical significance to date.

Authors:Neha Lad for the IceCube-Gen2 Collaboration

Abstract: The observation of an astrophysical neutrino flux in IceCube and its detection capability to separate between the different neutrino flavors has led IceCube to constraint the flavor content of this flux. IceCube-Gen2 is the planned extension of the current IceCube detector, which will be about 8 times larger than the current instrumented volume. In this work, we study the sensitivity of IceCube-Gen2 to the astrophysical neutrino flavor composition and investigate its tau neutrino identification capabilities. We apply the IceCube analysis on a simulated IceCube-Gen2 dataset that mimics the High Energy Starting Event (HESE) classification. Reconstructions are performed using sensors that have 3 times higher quantum efficiency and isotropic angular acceptance compared to the current IceCube optical modules. We present the projected sensitivity for 10 years of data on constraining the flavor ratio of the astrophysical neutrino flux at Earth by IceCube-Gen2.

Authors:Mikhail V. Beznogov, Adriana R. Raduta

Abstract: The equation of state (EOS) is a key ingredient for understanding the structure and composition of neutron stars (NSs). Observation of several pulsars with masses $\approx$ 2 Msun, inference of tidal deformabilities from gravitational waves signals in binary neutron stars mergers and joint mass and radius estimates of two millisecond pulsars contributed to better constraining the behavior of NS EOS beyond the nuclear saturation density. We aim to build families of EOSs subjected to various minimal sets of constraints and identify the role some of these constraints play. We also aim to establish correlations between properties of nuclear matter (NM) and properties of NSs. The non-relativistic mean field theory of NM and the standard Skyrme parametrization of the nucleonic effective interactions are used to generate, within a Bayesian framework, models of EOSs. The constraints we pose come from empirical parameters of NM, ab initio calculations of pure neutron matter (PNM) and the 2 Msun lower limit on the maximum NS mass. EOSs also have to be causal. A purely nucleonic composition is hypothesized. EOSs are generated and investigated for five sets of constraints. Marginalized posteriors of the effective interaction's parameters; empirical parameters of NM; selected global properties of NSs are plotted and analyzed. Correlations among parameters in the isoscalar and isovector channels as well as with NS properties are studied. EOSs of NM and NSs are very sensitive to the set of constraints, including whether correlations among the values that the energy per nucleon in PNM takes at different densities are accounted for. In each of the five sets that we have generated there is a significant number of models that comply at 50\% credible region with joint mass and radius constraints from PSR J0030+045 and J0740+6620, while a tension exists with similar data from the NS in HESS J1731--34.

Authors:Pablo Torne, Kuo Liu, Ralph P. Eatough, Jompoj Wongphechauxsorn, James M. Cordes, Gregory Desvignes, Mariafelicia De Laurentis, Michael Kramer, Scott M. Ransom, Shami Chatterjee, Robert Wharton, Ramesh Karuppusamy, Lindy Blackburn, Michael Janssen, Chi-kwan Chan, Geoffrey B. Crew, Lynn D. Matthews, Ciriaco Goddi, Helge Rottmann, Jan Wagner, Salvador Sanchez, Ignacio Ruiz, Federico Abbate, Geoffrey C. Bower, Juan J. Salamanca, Arturo I. Gomez-Ruiz, Alfredo Herrera-Aguilar, Wu Jiang, Ru-Sen Lu, Ue-Li Pen, Alexander W. Raymond, Lijing Shao, Zhiqiang Shen, Gabriel Paubert, Miguel Sanchez-Portal, Carsten Kramer, Manuel Castillo, Santiago Navarro, David John, Karl-Friedrich Schuster, Michael D. Johnson, Kazi L. J. Rygl, Kazunori Akiyama, Antxon Alberdi, Walter Alef, Juan Carlos Algaba, Richard Anantua, Keiichi Asada, Rebecca Azulay, Uwe Bach, Anne-Kathrin Baczko, David Ball, Mislav Balokovic, John Barrett, Michi Bauboeck, Bradford A. Benson, Dan Bintley, Raymond Blundell, Katherine L. Bouman, Hope Boyce, Michael Bremer, Christiaan D. Brinkerink, Roger Brissenden, Silke Britzen, Avery E. Broderick, Dominique Broguiere, Thomas Bronzwaer, Sandra Bustamante, Do-Young Byun, John E. Carlstrom, Chiara Ceccobello, Andrew Chael, Dominic O. Chang, Koushik Chatterjee, Ming-Tang Chen, Yongjun Chen, Xiaopeng Cheng, Ilje Cho, Pierre Christian, Nicholas S. Conroy, John E. Conway, Thomas M. Crawford, Alejandro Cruz-Osorio, Yuzhu Cui, Rohan Dahale, Jordy Davelaar, Roger Deane, Jessica Dempsey, Jason Dexter, Vedant Dhruv, Sheperd S. Doeleman, Sean Dougal, Sergio A. Dzib, Razieh Emami, Heino Falcke, Joseph Farah, Vincent L. Fish, Ed Fomalont, H. Alyson Ford, Marianna Foschi, Raquel Fraga-Encinas, William T. Freeman, Per Friberg, Christian M. Fromm, Antonio Fuentes, Peter Galison, Charles F. Gammie, Roberto Garcia, Olivier Gentaz, Boris Georgiev, Roman Gold, Jose L. Gomez, Minfeng Gu, Mark Gurwell, Kazuhiro Hada, Daryl Haggard, Kari Haworth, Michael H. Hecht, Ronald Hesper, Dirk Heumann, Luis C. Ho, Paul Ho, Mareki Honma, Chih-Wei L. Huang, Lei Huang, David H. Hughes, Shiro Ikeda, C. M. Violette Impellizzeri, Makoto Inoue, Sara Issaoun, David J. James, Buell T. Jannuzi, Britton Jeter, Alejandra Jimenez-Rosales, Svetlana Jorstad, Abhishek V. Joshi, Taehyun Jung, Mansour Karami, Tomohisa Kawashima, Garrett K. Keating, Mark Kettenis, Dong-Jin Kim, Jae-Young Kim, Jongsoo Kim, Junhan Kim, Motoki Kino, Jun Yi Koay, Prashant Kocherlakota, Yutaro Kofuji, Shoko Koyama, Thomas P. Krichbaum, Cheng-Yu Kuo, Noemi La Bella, Tod R. Lauer, Daeyoung Lee, Sang-Sung Lee, Po Kin Leung, Aviad Levis, Zhiyuan Li, Rocco Lico, Greg Lindahl, Michael Lindqvist, Mikhail Lisakov, Jun Liu, Elisabetta Liuzzo, Wen-Ping Lo, Andrei P. Lobanov, Laurent Loinard, Colin J. Lonsdale, Nicholas R. MacDonald, Jirong Mao, Nicola Marchili, Sera Markoff, Daniel P. Marrone, Alan P. Marscher, Ivan Marti-Vidal, Satoki Matsushita, Lia Medeiros, Karl M. Menten, Daniel Michalik, Izumi Mizuno, Yosuke Mizuno, James M. Moran, Kotaro Moriyama, Monika Moscibrodzka, Cornelia Muller, Hendrik Muller, Alejandro Mus, Gibwa Musoke, Ioannis Myserlis, Andrew Nadolski, Hiroshi Nagai, Neil M. Nagar, Masanori Nakamura, Ramesh Narayan, Gopal Narayanan, Iniyan Natarajan, Antonios Nathanail, Joey Neilsen, Roberto Neri, Chunchong Ni, Aristeidis Noutsos, Michael A. Nowak, Junghwan Oh, Hiroki Okino, Hector Olivares, Gisela N. Ortiz-Leon, Tomoaki Oyama, Feryal Ozel, Daniel C. M. Palumbo, Georgios Filippos Paraschos, Jongho Park, Harriet Parsons, Nimesh Patel, Dominic W. Pesce, Vincent Pietu, Richard Plambeck, Aleksandar PopStefanija, Oliver Porth, Felix M. Potzl, Ben Prather, Jorge A. Preciado-Lopez, Dimitrios Psaltis, Hung-Yi Pu, Venkatessh Ramakrishnan, Ramprasad Rao, Mark G. Rawlings, Luciano Rezzolla, Angelo Ricarte, Bart Ripperda, Freek Roelofs, Alan Rogers, Eduardo Ros, Cristina Romero-Cañizales, Arash Roshanineshat, Alan L. Roy, Chet Ruszczyk, David Sanchez-Arguelles, Mahito Sasada, Kaushik Satapathy, Tuomas Savolainen, F. Peter Schloerb, Jonathan Schonfeld, Zhiqiang Shen, Des Small, Bong Won Sohn, Jason SooHoo, Kamal Souccar, He Sun, Alexandra J. Tetarenko, Paul Tiede, Remo P. J. Tilanus, Michael Titus, Teresa Toscano, Efthalia Traianou, Tyler Trent, Sascha Trippe, Matthew Turk, Ilse van Bemmel, Huib Jan van Langevelde, Daniel R. van Rossum, Jesse Vos, Derek Ward-Thompson, John Wardle, Jonathan Weintroub, Norbert Wex, Maciek Wielgus, Kaj Wiik, Gunther Witzel, Michael F. Wondrak, George N. Wong, Qingwen Wu, Nitika Yadlapalli, Paul Yamaguchi, Aristomenis Yfantis, Doosoo Yoon, Andre Young, Ken Young, Ziri Younsi, Wei Yu, Feng Yuan, Ye-Fei Yuan, J. Anton Zensus, Shuo Zhang, Guang-Yao Zhao, Shan-Shan Zhao

Abstract: The Event Horizon Telescope (EHT) observed in 2017 the supermassive black hole at the center of the Milky Way, Sagittarius A* (Sgr A*), at a frequency of 228.1 GHz ($\lambda$=1.3 mm). The fundamental physics tests that even a single pulsar orbiting Sgr A* would enable motivate searching for pulsars in EHT datasets. The high observing frequency means that pulsars - which typically exhibit steep emission spectra - are expected to be very faint. However, it also negates pulse scattering, an effect that could hinder pulsar detections in the Galactic Center. Additionally, magnetars or a secondary inverse Compton emission could be stronger at millimeter wavelengths than at lower frequencies. We present a search for pulsars close to Sgr A* using the data from the three most-sensitive stations in the EHT 2017 campaign: the Atacama Large Millimeter/submillimeter Array, the Large Millimeter Telescope and the IRAM 30 m Telescope. We apply three detection methods based on Fourier-domain analysis, the Fast-Folding-Algorithm and single pulse search targeting both pulsars and burst-like transient emission; using the simultaneity of the observations to confirm potential candidates. No new pulsars or significant bursts were found. Being the first pulsar search ever carried out at such high radio frequencies, we detail our analysis methods and give a detailed estimation of the sensitivity of the search. We conclude that the EHT 2017 observations are only sensitive to a small fraction ($\lesssim$2.2%) of the pulsars that may exist close to Sgr A*, motivating further searches for fainter pulsars in the region.

Authors:Zhao-Yang Xia, Yuan-Pei Yang, Qiao-Chu Li, Fa-Yin Wang, Bo-Yang Liu, Zi-Gao Dai

Abstract: Recently, some fast radio bursts (FRBs) have been reported to exhibit complex and diverse variations in Faraday rotation measurements (RM) and polarization, suggesting that dynamically evolving magnetization environments may surround them. In this paper, we investigate the Faraday conversion (FC) effect in a binary system involving an FRB source and analyze the polarization evolution of FRBs. For an strongly magnetized high-mass companion binary (HMCB), when an FRB with $\sim100\%$ linear polarization passes through the radial magnetic field of the companion star, the circular polarization (CP) component will be induced and oscillate symmetrically around the point with the CP degree equal to zero, the rate and amplitude of the oscillation decrease as the frequency increases. The very strong plasma column density in the HMCBs can cause CP to oscillate with frequency at a very drastic rate, which may lead to depolarization. Near the superior conjunction of the binary orbit, the DM varies significantly due to the dense plasma near the companion, and the significant FC also occurs in this region. As the pulsar moves away from the superior conjunction, the CP gradually tends towards zero and then returns to its value before incidence. We also investigate the effect of the rotation of the companion star. We find that a sufficiently significant RM reversal can be produced at large magnetic inclinations and the RM variation is very diverse. Finally, we apply this model to explain some polarization observations of PSR B1744-24A and FRB 20201124A.

Authors:Pavan A. Uttarkar, R. M. Shannon, K. Gourdji, A. T. Deller, C. K. Day, S. Bhandari

Abstract: Fast Radio Bursts (FRBs) are extragalactic transients of (sub-)millisecond duration that show wide-ranging spectral, temporal, and polarimetric properties. The polarimetric analysis of FRBs can be used to probe intervening media, study the emission mechanism, and test possible progenitor models. In particular, low frequency depolarisation of FRBs can identify dense, turbulent, magnetised, ionised plasma thought to be near the FRB progenitor. An ensemble of repeating FRBs has shown low-frequency depolarisation. The depolarisation is quantified by the parameter $\sigma_{\rm RM}$, which correlates with proxies for both the turbulence and mean magnetic field strength of the putative plasma. However, while many non-repeating FRBs show comparable scattering (and hence inferred turbulence) to repeating FRBs, it is unclear whether their surrounding environments are comparable to those of repeating FRBs. To test this, we analyse the spectro-polarimetric properties of five one-off FRBs and one repeating FRB, detected and localised by the Australian Square Kilometer Array Pathfinder. We search for evidence of depolarisation due to $\sigma_{\rm RM}$ and consider models where the depolarisation is intrinsic to the source. We find no evidence (for or against) the sample showing spectral depolarisation. Under the assumption that FRBs have multipath propagation-induced depolarisation, the correlation between our constraint on $\sigma_{\rm RM}$ and RM is consistent with repeating FRBs only if the values of $\sigma_{\rm RM}$ are much smaller than our upper limits. The observations provide further evidence for differences in the environments and sources of one-off and repeating FRBs.

Authors:Shu-Rui Zhang USTC, Yan Luo USTC, Xiao-Jun Wu USTC, Jian-Min Wang IHEP, Luis C. Ho PKU, Ye-Fei Yuan USTC

Abstract: In the inner region of the disc of an active galactic nucleus (AGN), the collision of two white dwarfs (WDs) through Jacobi capture might be inevitable, leading to a Type Ia supernova (SN Ia) explosion. This transient event, influenced by the disc gas and the gravity of the supermassive black hole (SMBH), exhibits distinct characteristics compared to normal SNe Ia. The energy of the explosion is mainly stored in the ejecta in the form of kinetic energy. Typically, the ejecta is not effectively decelerated by the AGN disc and rushes rapidly out of the AGN disc. However, under the influence of the SMBH, most of the ejecta falls back toward the AGN disc. As the fallback ejecta becomes more dispersed, it interacts with the disc gas, converting its kinetic energy into thermal energy. This results in a high-energy transient characterized by a rapid initial rise followed by a decay with $L\propto t^{-2.8}$. The time-scale of the transient ranges from hours to weeks, depending on the mass of the SMBH. This process generates high-energy radiation spanning from hard X-rays to the soft $\gamma$ range. Additionally, the subsequent damage to the disc may result in changing-look AGNs. Moreover, the falling back of SNe Ia ejecta onto the AGN disc significantly increases the metallicity of the AGN and can even generate heavy elements within the AGN discs.

Authors:Saurabh, Parth Bambhaniya, Pankaj S. Joshi

Abstract: Recent Event Horizon Telescope observations of M87* and Sgr A* strongly suggests the presence of supermassive black hole at their respective cores. In this work, we use the semi-analytic Radiatively Inefficient Accretion Flows (RIAF) model to investigate the resulting images of Joshi-Malafarina-Narayan (JMN-1) naked singularity and the Schwarzschild BH. We aim at choosing the JMN-1 naked singularity model and compare the synchrotron images with the Schwarzschild solution to search any distinct features which can distinguish the two objects and find alternative to the black hole solution. We perform general relativistic ray-tracing and radiative transfer simulations using Brahma code to generate synchrotron emission images utilising thermal distribution function for emissivity and absorptivity. We investigate effects in the images by varying inclination angle, disk width and frequency. The shadow images simulated by the JMN-1 model closely resemble those generated by the Schwarzschild black hole. When we compare these images, we find that the disparities between them are minimal. We conduct simulations using various plasma parameters, but the resulting images remain largely consistent for both scenarios. This similarity is evident in the horizontal cross-sectional brightness profiles of the two instances. Notably, the JMN-1 model exhibits slightly higher intensity in comparison to the Schwarzschild black hole. We conclude that JMN-1 presents itself as a viable substitute for the black hole scenario. This conclusion is not solely grounded in the fact that they are indistinguishable from their respective shadow observations, but also in the consideration that JMN-1 emerges as an end state of a continual gravitational collapse. This paradigm not only allows for constraints on spacetime but also provides a good probe for the nature of the central compact object.

Authors:Antonio Galván, Nissim Fraija, Edilberto Aguilar-Ruiz, Jose Antonio de Diego Onsurbe, Maria G. Dainotti

Abstract: Besides the neutrino source detected by IceCube, NGC 1068, the association of the IceCube-170922A neutrino with the blazar in a flaring state among several wavelengths (from radio up to high-energy (HE) gamma-rays), the site and mechanisms of production of HE neutrino remains in discussion. Extragalactic sources such as Quasars, Blazars, Radio galaxies, and Gamma-ray bursts have been proposed as progenitors of HE neutrinos. In this work, we study the Blazars reported by Fermi-LAT in the 4LAC catalog, which are embedded inside the 90\% error of the best-fit position from the neutrinos reported by IceCube. We propose a one-zone lepto-hadronic scenario to describe the broadband Spectral Energy Distribution and then estimate the number of neutrinos to compare with those in the direction of each source. A brief discussion is provided of the results.

Authors:Vincenzo Sapienza, Marco Miceli, Oleh Petruk, Aya Bamba, Salvatore Orlando, Fabrizio Bocchino, Giovanni Peres

Abstract: The maximum energy of electrons accelerated by supernova remnants (SNR) is typically limited by radiative losses. In this scenario, the synchrotron cooling time scale is equal to the acceleration time scale. On the other hand, the low propagation speed of a shock in a dense medium is expected to result in an extended acceleration time scale, thus inducing a decrease in the maximum electron energy for a given SNR age and in the X-ray nonthermal flux. The young Kepler's SNR shows an enhanced efficiency of the acceleration process, which is close to the Bohm limit in the north of its shell, where the shock is slowed down by a dense circumstellar medium. Conversely, in the south, where no interaction with a dense medium is evident and the shock speed is high, the acceleration proceeds with a higher Bohm factor. To investigate this scenario, we studied the temporal evolution of the non-thermal emission, taking advantage of two Chandra X-ray observations of Kepler's SNR (performed in 2006 and 2014). We analyzed the spectra of different filaments both in the north and south of the shell, and measured their proper motion. We found a region with low shock velocity where we measured a significant decrease in flux from 2006 to 2014. This could be the first evidence of fading synchrotron emission in Kepler's SNR. This result suggests that under a certain threshold of shock speed the acceleration process could exit the loss-limited regime.

Authors:Chen Li, Jelle S. Kaastra, Liyi Gu, Missagh Mehdipour

Abstract: Outflowing wind as one type of AGN feedback, which involves noncollimated ionized winds prevalent in Seyfert-1 AGNs, impacts their host galaxy by carrying kinetic energy outwards. However, the distance of the outflowing wind is poorly constrained due to a lack of direct imaging observations, which limits our understanding of their kinetic power and therefore makes the impact on the local galactic environment unclear. One potential approach involves a determination of the density of the ionized plasma, making it possible to derive the distance using the ionization parameter {\xi}, which can be measured based on the ionization state. Here, by applying a new time-dependent photoionization model, tpho, in SPEX, we define a new approach, the tpho-delay method, to calculate/predict a detectable density range for warm absorbers of NGC 3783. The tpho model solves self-consistently the time-dependent ionic concentrations, which enables us to study delayed states of the plasma in detail. We show that it is crucial to model the non-equilibrium effects accurately for the delayed phase, where the non-equilibrium and equilibrium models diverge significantly. Finally, we calculate the crossing time to consider the effect of the transverse motion of the outflow on the intrinsic luminosity variation. It is expected that future spectroscopic observations with more sensitive instruments will provide more accurate constraints on the outflow density, and thereby on the feedback energetics.

Authors:Karlijn Kruiswijk Centre for Cosmology, Particle Physics and Phenomenology - CP3, Université catholique de Louvain, Louvain-la-Neuve, Belgium, Gwenhaël de Wasseige Centre for Cosmology, Particle Physics and Phenomenology - CP3, Université catholique de Louvain, Louvain-la-Neuve, Belgium

Abstract: While Gamma-Ray Burst (GRBs) are clear and distinct observed events, every individual GRB is unique. In fact, GRBs are known for their variable behaviour, and BATSE was already able to discover two categories of GRB from the T90 distribution; the short and long GRBs. These two categories match up with the expected two types of GRB progenitors. Nowadays, more features have been found to be able to further distinguish them, such as the hardness ratio or the presence of supernovae. However, that does not mean that it is by any means simple to categorise individual GRBs. Furthermore, more GRB categories have been theorised as well, such as low-luminosity or X-ray-rich GRBs. These different types of GRBs also could indicate a different neutrino spectrum, with different types of GRBs more likely to emit higher amounts of neutrinos. We present an ongoing effort to use machine learning to categorise and classify GRBs, searching for subpopulations that could yield a larger neutrino flux. We specifically use unsupervised learning, as it allows hidden patterns and correlations to come to light. With the help of features such as the T90, hardness, fluence, SNR, spectral index and even the full light curve and spectra, different structures and categories of Gamma-Ray bursts can be found.

Authors:Hongtao Wang, Chao Guo, Hongmin Cao, Yongyun Chen, Nan Ding, Xiaotong Guo

Abstract: By means of the data sets of the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS), we investigate the relationship between the variability amplitude and luminosity at 5100 \AA, black hole mass, Eddington ratio, $ R_{\rm Fe \, II}$ ( the ratio of the flux of Fe II line within 4435-4685 \AA ~to the broad proportion of $\rm H\beta$ line) as well as $ R_{5007}$ (the ratio of the flux [O III] line to the total $\rm H\beta$ line) of the broad line Seyfert 1 (BLS1) and narrow line Seyfert 1 (NLS1) galaxies sample in g,r,i,z and y bands, respectively. We also analyze the similarities and differences of the variability characteristics between the BLS1 galaxies and NLS1 galaxies. The results are listed as follows. (1). The cumulative probability distribution of the variability amplitude shows that NLS1 galaxies are lower than that in BLS1 galaxies. (2). We analyze the dependence of the variability amplitude with the luminosity at 5100 \AA, black hole mass, Eddington ratio, $ R_{\rm Fe \,II}$ and $ R_{5007}$, respectively. We find significantly negative correlations between the variability amplitude and Eddington ratio, insignificant correlations with the luminosity at 5100 \AA. The results also show significantly positive correlations with the black hole mass and $ R_{5007}$, significantly negative correlations with $ R_{\rm Fe\, II}$ which are consistent with Rakshit and Stalin(2017) in low redshift bins (z<0.4) and Ai et al.(2010). (3). The relationship between the variability amplitude and the radio loudness is investigated for 155 BLS1 galaxies and 188 NLS1 galaxies. No significant correlations are found in our results.

Authors:Janeth Valverde for the Fermi-LAT Collaboration, D. Kocevski for the Fermi-LAT Collaboration, M. Negro for the Fermi-LAT Collaboration, S. Garrappa for the Fermi-LAT Collaboration, A. Brill for the Fermi-LAT Collaboration

Abstract: For over 15 years the Fermi Large Area Telescope (Fermi-LAT) has been monitoring the entire high-energy gamma-ray sky, providing the best sampled 0.1 -- $>1$ TeV photons to this day. As a result, the Fermi-LAT has been serving the time-domain and multi-messenger community as the main source of gamma-ray activity alerts. All of this makes the Fermi-LAT a key instrument towards understanding the underlying physics behind the most extreme objects in the universe. However, generating mission-long LAT light curves can be very computationally expensive. The Fermi-LAT light curve repository (LCR) tackles this issue. The LCR is a public library of gamma-ray light curves for 1525 Fermi-LAT sources deemed variable in the 4FGL-DR2 catalog. The repository consists of light curves on timescales of days, weeks, and months, generated through a full-likelihood unbinned analysis of the source and surrounding region, providing flux and photon index measurements for each time interval. Hosted at NASA's FSSC, the library provides users with access to this continually updated light curve data, further serving as a resource to the time-domain and multi-messenger communities.

Authors:Artem Bohdan, Anabella Araudo, Allard Jan van Marle, Fabien Casse, Alexandre Marcowith

Abstract: Astrophysical shocks create cosmic rays by accelerating charged particles to relativistic speeds. However, the relative contribution of various types of shocks to the cosmic ray spectrum is still the subject of ongoing debate. Numerical studies have shown that in the non-relativistic regime, oblique shocks are capable of accelerating cosmic rays, depending on the Alfv\'enic Mach number of the shock. We now seek to extend this study into the mildly relativistic regime. In this case, dependence of the ion reflection rate on the shock obliquity is different compared to the nonrelativistic regime. Faster relativistic shocks are perpendicular for the majority of shock obliquity angles therefore their ability to initialize efficient DSA is limited. We define the ion injection rate using fully kinetic PIC simulation where we follow the formation of the shock and determine the fraction of ions that gets involved into formation of the shock precursor in the mildly relativistic regime covering a Lorentz factor range from 1 to 3. Then, with this result, we use a combined PIC-MHD method to model the large-scale evolution of the shock with the ion injection recipe dependent on the local shock obliquity. This methodology accounts for the influence of the self-generated or pre-existing upstream turbulence on the shock obliquity which allows study substantially larger and longer simulations compared to classical hybrid techniques.

Authors:Chiara Bellenghi for the IceCube Collaboration, Martina Karl for the IceCube Collaboration, Martin Wolf for the IceCube Collaboration

Abstract: Searching for the sources of high-energy cosmic particles requires sophisticated analysis techniques, frequently involving hypothesis tests with unbinned log-likelihood (LLH) functions. SkyLLH is an open-source, Python-based software tool to build these LLH functions and perform likelihood-ratio tests. We present a new easy-to-use and modular extension of SkyLLH that allows the user to perform neutrino point source searches in the entire sky using ten years of IceCube public data. To guide the user, SkyLLH provides tutorials showing how to analyze the experimental data and calculate useful statistical quantities. Here we describe the details of the analysis workflow and illustrate some of the possible methods to work with the IceCube public dataset. Additionally, we show that SkyLLH can reproduce the results from a previous IceCube publication that used the public data release. We obtain a similar local significance for the neutrino emission from a list of candidate sources within a maximum shift of 0.5$\sigma$. Finally, the measured neutrino flux from the most significant source candidate, NGC 1068, shows substantial agreement with the previously published result.

Authors:Chiara Bellenghi for the IceCube Collaboration, Martin Ha Minh for the IceCube Collaboration, Tomas Kontrimas for the IceCube Collaboration, Elena Manao for the IceCube Collaboration, Rasmus Ørsøe for the IceCube Collaboration, Martin Wolf for the IceCube Collaboration

Abstract: The IceCube Neutrino Observatory is a one-cubic-kilometer-sized neutrino telescope deployed deep in the Antarctic ice at the South Pole. One of IceCube's major goals is finding the origins of astrophysical high-energy neutrinos. In 2022, IceCube identified the strongest point-like neutrino source so far, the active galaxy NGC 1068. Analyzing 9 years of muon-neutrino data from the Northern Sky recorded between 2011 and 2020, the emission from NGC 1068 is significant at 4.2$\,\sigma$. We present a planned extension to this search with additional years of data. One of these years includes data from 2010 when IceCube was only partially constructed. We discuss the improvement in sensitivity and discovery potential for neutrino point sources across the Northern sky. We show that by building on the established analysis techniques, previous observations could be improved, not only for NGC 1068 but for all possible sources in the Northern sky.

Authors:Lisa Johanna Schumacher, Foteini Oikonomou

Abstract: The discovery of high-energy astrophysical neutrinos in the TeV-PeV range by IceCube marked the start of neutrino astronomy, and the search for their sources continues. Two promising source candidates have been identified by IceCube: NGC 1068 in the 1 TeV-10 TeV range and TXS 0506+056 in the 0.1-1 PeV range. Both sources have gamma-ray counterparts, but additional time information of both neutrinos and gamma rays were essential for the identification of TXS 0506+056. The Planetary Neutrino Monitoring (PLEnuM) concept is an approach for combining the exposures of all current and future neutrino observatories - such as KM3NeT, Baikal-GVD, P-ONE in the Northern Hemisphere, and IceCube-Gen2 in the Southern Hemisphere. Using this PLEnuM approach, we estimate how the detection capability for transient sources candidates like blazars and GRBs improves once the future neutrino observatories come online. In addition, we present how the combined, instantaneous field of view of PLEnuM improves the real-time detection rate of rare, very-high-energy neutrinos across the entire sky.

Authors:Shivani Bhandari, Benito Marcote, Navin Sridhar, Tarraneh Eftekhari, Jason W. T. Hessels, Danté M. Hewitt, Franz Kirsten, Omar S. Ould-Boukattine, Zsolt Paragi, Mark P. Snelders

Abstract: We present very-long-baseline interferometry (VLBI) observations of a continuum radio source potentially associated with the fast radio burst source FRB 20190520B. Using the European VLBI network (EVN), we find the source to be compact on VLBI scales with an angular size of $<2.3$ mas ($3\sigma$). This corresponds to a transverse physical size of $<9$ pc (at the $z=0.241$ redshift of the host galaxy), confirming it to be an FRB persistent radio source (PRS) like that associated with the first-known repeater FRB 20121102A. The PRS has a flux density of $201 \pm 34 \rm{\mu Jy}$ at 1.7 GHz and a spectral radio luminosity of $L_{1.7 \rm GHz} = (3.0 \pm 0.5) \times 10^{29}\,\mathrm{erg s^{-1} Hz^{-1}}$ (also similar to the FRB 20121102A PRS). Comparing to previous lower-resolution observations, we find that no flux is resolved out on milliarcsecond scales. We have refined the PRS position, improving its precision by an order of magnitude compared to previous results. We also report the detection of a FRB 20190520B burst at 1.4 GHz and find the burst position to be consistent with the PRS position, at $\lesssim20$ mas. This strongly supports their direct physical association and the hypothesis that a single central engine powers both the bursts and the PRS. We discuss the model of a magnetar in a wind nebula and present an allowed parameter space for its age and the radius of the putative nebula powering the observed PRS emission. Alternatively, we find that an accretion-powered 'hypernebula' model also fits our observational constraints.

Authors:Nikhil Sarin, Moritz Hübner, Conor M. B. Omand, Christian N. Setzer, Steve Schulze, Naresh Adhikari, Ana Sagués-Carracedo, Shanika Galaudage, Wendy F. Wallace, Gavin P. Lamb, En-Tzu Lin

Abstract: Fulfilling the rich promise of rapid advances in time-domain astronomy is only possible through confronting our observations with physical models and extracting the parameters that best describe what we see. Here, we introduce {\sc Redback}; a Bayesian inference software package for electromagnetic transients. {\sc Redback} provides an object-orientated {\sc python} interface to over 12 different samplers and over 100 different models for kilonovae, supernovae, gamma-ray burst afterglows, tidal disruption events, engine-driven transients, X-ray afterglows of gamma-ray bursts driven by millisecond magnetars among other explosive transients. The models range in complexity from simple analytical and semi-analytical models to surrogates built upon numerical simulations accelerated via machine learning. {\sc Redback} also provides a simple interface for downloading and processing data from Swift, Fink, Lasair, the open-access catalogues, and BATSE and fit this or private data. {\sc Redback} can also be used as an engine to simulate transients for telescopes such as the Zwicky Transient Facility and Vera Rubin with realistic cadences, limiting magnitudes, and sky-coverage or a hypothetical user-constructed survey with arbitrary settings. We also provide a more general simulation interface suitable for target of opportunity observations with different telescopes. We demonstrate through a series of examples how {\sc Redback} can be used as a tool to simulate a large population of transients for realistic surveys, fit models to real, simulated, or private data, multi-messenger inference and serve as an end-to-end software toolkit for parameter estimation and interpreting the nature of electromagnetic transients.

Authors:Subhankar Patra, Bibhas Ranjan Majhi, Santabrata Das

Abstract: In this paper, we study the properties of accretion flow including its spectral features in Johannsen and Psaltis (JP) non-Kerr spacetime. In doing so, we numerically solve the governing equations that describe the flow motion around the compact objects in a general relativistic framework, where spin ($a_{k}$) and deformation parameters ($\varepsilon$) demonstrate the nature of the central source, namely black hole (BH) or naked singularity (NS). With this, we obtain all possible classes of global accretion solutions ($i. e.$, O, A, W and I-type) by varying the energy ($E$) and angular momentum ($\lambda$) of the relativistic accretion flow, and examine the role of thermal bremsstrahlung emission in studying the spectral energy distributions (SEDs) of the accretion disc. We divide the parameter space in $\lambda-E$ plane in terms of the different classes of accretion solutions for BH and NS models. We further calculate the disc luminosity ($L$) corresponding to these accretion solutions, and observe that I-type solutions yield higher $L$ and SEDs than the remaining types of solutions for both BH and NS models. For BH model, SEDs for W and I-type solutions differ significantly from the results for O and A-type solutions for low $E$ values. On the contrary, for NS model, SEDs for different accretion solutions are identical in the whole parameter space of $\lambda$ and $E$. We also examine the effect of $\varepsilon$ on the SEDs and observe that a non-Kerr BH yields higher SEDs than the usual Kerr BH. Finally, for accretion solutions of identical $E$ and $\lambda$, we compare the SEDs obtained from BH and NS models, and find that naked singularity objects produce more luminous power spectra than the black holes.

Authors:Yves Kini, Tuomo Salmi, Serena Vinciguerra, Anna L. Watts, Devarshi Choudhury, Slavko Bogdanov, Johannes Buchner, Zach Meisel, Valery Suleimanov

Abstract: Pulse profile modelling is a relativistic ray-tracing technique that can be used to infer masses, radii and geometric parameters of neutron stars. In a previous study, we looked at the performance of this technique when applied to thermonuclear burst oscillations from accreting neutron stars. That study showed that ignoring the variability associated with burst oscillation sources resulted in significant biases in the inferred mass and radius, particularly for the high count rates that are nominally required to obtain meaningful constraints. In this follow-on study, we show that the bias can be mitigated by slicing the bursts into shorter segments where variability can be neglected, and jointly fitting the segments. Using this approach, the systematic uncertainties on the mass and radius are brought within the range of the statistical uncertainty. With about 10$^6$ source counts, this yields uncertainties of approximately 10% for both the mass and radius. However, this modelling strategy requires substantial computational resources. We also confirm that the posterior distributions of the mass and radius obtained from multiple bursts of the same source can be merged to produce outcomes comparable to that of a single burst with an equivalent total number of counts.

Authors:Alexander B. Igl Louisiana State University, Robert I. Hynes Louisiana State University, Christopher T. Britt Space Telescope Science Institute, Kieren S. O'Brien Durham University, Valerie J. Mikles NASA Goddard Space Flight Center

Abstract: We observed the low-mass X-ray binary Sco X-1 for 12 nights simultaneously using the Rossi X-Ray Timing Explorer and the Otto Struve Telescope at McDonald Observatory at 1 second time resolution. This is among the most comprehensive simultaneous X-Ray/optical data sets of Sco X-1. Evidence of reprocessing was observed in the form of nine positive, near-zero lag peaks in the cross correlation function, eight of which were relatively small and took the shape of piecewise exponential functions. These peaks were initially identified by eye, after which a computational identification scheme was developed to confirm their significance. Based on their short lags (less than 4 seconds), as well as their occurrence on the flaring branch and soft apex, the small cross correlation features are likely to be caused by reprocessing off the outer disc, although the companion could still make a contribution to their tails. The Z track was parameterized using a rank number scheme so that the system's location on the track could be numerically defined. Plotting the results against the optical reveals an increasing step function when moving from the horizontal to the normal to the flaring branch, with differential optical levels at ~0.47, ~0.57, and ~1.1 respectively. An additional correlation between Z track location and the optical was found on the upper flaring branch. An optical intensity histogram reveals a transition region between the normal and flaring branches with only intermediate fluxes.

Authors:Xudong Wen, He Gao, Shunke Ai, liangduan liu, Jin-Ping Zhu, Wei-Hua Lei

Abstract: The formation of black hole-neutron star (BH-NS) or BH-BH systems may be accompanied with special supernova (SN) signals, due to the accretion feedback from the companion BH. The additional heating, which is mainly attributed to the Blandford-Payne mechanism, would disrupt the isotropic nature of the luminosity distribution on the surface of the SN ejecta, leading to the appearance of polarization. Here we develop a three dimensional (3D) Monte Carlo polarization simulation code (MCPSC) to conduct simulations for these special SNe. We find that the maximum polarization level of approximately \sim 2 occurs at the peak time of SN emission in the "close-binary" scenario, while in the "faraway-binary" case, maximum polarization (i.e. \sim 0.7) is observed at a considerably later time than the peak of the SN. The magnitude of polarization is dependent on the degree of unevenness in the luminosity distribution and the angle between the line of sight and the equatorial direction. When considering the geometric distortion of supernova ejecta at the same time, the magnitude of polarization may either increase (for a oblate ellipsoidal shape) or decrease (for a prolate ellipsoidal shape). The polarization signatures represent a promising auxiliary instrument to facilitate the identification of the companion-fed SNe. Moreover, by comparing the event rate of these special SNe with the event rate density of LIGO-Virgo detected BH-NS/BH systems could further help to distinguish the BH-NS/BH formation channel.

Authors:Shunsuke Sakurai The FAST Collaboration, Justin Albury The FAST Collaboration, Jose Bellido The FAST Collaboration, Fraser Bradfield The FAST Collaboration, Ladislav Chytka The FAST Collaboration, John Farmer The FAST Collaboration, Toshihiro Fujii The FAST Collaboration, Petr Hamal The FAST Collaboration, Pavel Horvath The FAST Collaboration, Miroslav Hrabovsky The FAST Collaboration, Vlastimil Jilek The FAST Collaboration, Jakub Kmec The FAST Collaboration, Jiri Kvita The FAST Collaboration, Max Malacari The FAST Collaboration, Dusan Mandat The FAST Collaboration, Massimo Mastrodicasa The FAST Collaboration, John N. Matthews The FAST Collaboration, Stanislav Michal The FAST Collaboration, Hiromu Nagasawa The FAST Collaboration, Hiroki Namba The FAST Collaboration, Libor Nozka The FAST Collaboration, Miroslav Palatka The FAST Collaboration, Miroslav Pech The FAST Collaboration, Paolo Privitera The FAST Collaboration, Francesco Salamida The FAST Collaboration, Petr Schovanek The FAST Collaboration, Radomir Smida The FAST Collaboration, Daniel Stanik The FAST Collaboration, Zuzana Svozilikova The FAST Collaboration, Akimichi Taketa The FAST Collaboration, Kenta Terauch The FAST Collaboration, Stan B. Thomas The FAST Collaboration, Petr Travnicek The FAST Collaboration, Martin Vacula The FAST Collaboration

Abstract: Ultra-high energy cosmic rays (UHECRs), whose energy are beyond $10^{18}~\mathrm{eV}$, are the most energetic particles we have ever detected. The latest results seem to indicate a heavier composition at the highest energies, complicating the search for their origins. Due to the limited number of UHECR events, we need to build an instrument with an order of magnitude larger effective-exposure to collect UHECRs in future decades. The Fluorescence detector Array of Single-pixel Telescopes (FAST) is a proposed low-cost, easily deployable UHECR detector suitable for a future ground array. It is essential to validate the telescope design and autonomous observational techniques using prototypes located in both hemispheres. Here we report on the current status of observations, recent performance results of prototypes, and developments towards a future mini-array.

Authors:M. Khurana, A. Pathania, K. K. Singh, C. Borwankar, P. K. Netrakanti, K. K. Yadav

Abstract: The MACE (Major Atmospheric Cherenkov Experiment) telescope has started its regular gamma-ray observations at Hanle in India. Located at an altitude of $\sim$ 4.3 km above sea level and equipped with a 21 m diameter large quasi-parabolic reflector, it has the capability to explore the gamma-ray sky in the energy range above 20 GeV with very high sensitivity. In this work, we present the results from the feasibility studies for searching high-energy gamma-ray signals from dark matter interaction in potential astrophysical environments. We study the impact of MACE response function and other instrumental characteristics to probe the velocity average interaction cross-section ($<\sigma v>$) of the weakly interacting massive particles (WIMPs), expected from the thermal dark matter freeze-out during the decoupling era. We consider the presence of dark matter in the form of pure WIMPs in the mass range 200 GeV - 10 TeV to produce distinctive gamma-ray spectra through its self-annihilation into standard model particles using the Pythia simulation package. The convolution of gamma-ray spectra corresponding to different standard model channels with the MACE response function is used to estimate the upper limit on $<\sigma v>$ for 100 hours of expected MACE observation of Segue1 (a dwarf spheroidal galaxy) which is a potential site of dark matter.

Authors:Danté M. Hewitt, Jason W. T. Hessels, Omar S. Ould-Boukattine, Pragya Chawla, Ismaël Cognard, Akshatha Gopinath, Lucas Guillemot, Daniela Huppenkothen, Kenzie Nimmo6, Mark P. Snelders

Abstract: We report on exceptionally bright bursts (>400 Jy ms) detected from the repeating fast radio burst source FRB 20220912A using the Nan\c{c}ay Radio Telescope (NRT), as part of the ECLAT (Extragalactic Coherent Light from Astrophysical Transients) monitoring campaign. These bursts exhibit extremely luminous, broadband, short-duration structures (~ 16 microseconds), which we term 'microshots' and which can be especially well studied in the NRT data given the excellent signal-to-noise and dynamic range (32-bit samples). The estimated peak flux density of the brightest microshot is 450 Jy. We show that the microshots are clustered into dense 'forests', by modelling them as Weibull distributions and obtaining Weibull shape parameters of approximately 0.5. Our polarimetric analysis reveals that the bursts are nearly 100% linearly polarised; have < 10% circular polarisation fractions; a near-zero average rotation measure of 0.10(6) rad/m^2; and varying polarisation position angles over the burst duration. For one of the bursts, we analyse raw voltage data from simultaneous observations with the Westerbork RT-1 single 25-m dish. These data allow us to measure the scintillation bandwidth, 0.30(3) MHz, and to probe the bursts on (sub-)microsecond timescales. Some important nuances related to dedispersion are also discussed. We propose that the emission mechanism for the broadband microshots is potentially different from the emission mechanism of the broader burst components which still show a residual drift of a few hundred MHz/ms after correcting for dispersion using the microshots. We discuss how the observed emission is phenomenologically analogous to different types of radio bursts from the Sun.

Authors:Paramita Dasgupta for the ARA Collaboration, Marco Stein Muzio for the ARA Collaboration

Abstract: The Askaryan Radio Array (ARA) is an in-ice ultrahigh energy (UHE, $>10$ PeV) neutrino experiment at the South Pole that aims to detect radio emissions from neutrino-induced particle cascades. ARA has five independent stations which together have collected nearly 24 station-years of data. Each of these stations search for UHE neutrinos by burying in-ice clusters of antennas $\sim 200$ m deep in a roughly cubical lattice with side length $\sim 15$ m. Additionally, the fifth ARA station (A5) has a beamforming trigger, referred to as the Phased Array (PA), consisting of a trigger array of 7 tightly packed vertically-polarized antennas. In this proceeding, we will present a neutrino search with the data of this "hybrid" station, emphasizing its capabilities for improved analysis efficiencies, background rejection, and neutrino vertex reconstruction. This is enabled by combining the closely packed trigger antennas with the long-baselines of the outrigger antennas. We will also place the A5 analysis into the context of the broader five station analysis program, including efforts to characterize and calibrate the detector, model and constrain backgrounds, and reject noise across the entire array. We anticipate this full neutrino search to set world-leading limits above 100 PeV, and inform the next generation of neutrino detection experiments.

Authors:A. Filócomo, J. F. Albacete Colombo, E. Mestre, L. J. Pellizza, J. A. Combi

Abstract: NGC 2071 is a star-forming region that overlaps with three $\gamma$-ray sources detected by the Fermi Space Telescope. We propose that strong flare activity in T Tauri stars could produce $\gamma$-ray emission in a way that makes them a counterpart to some unidentified sources detected by the Large Area Telescope aboard the Fermi satellite. We have performed a spectral and temporal analysis for two Fermi data sets: the first 2 yr and the entire 14 yr of observations. We have found that the $\gamma$-ray source is detectable at 3.2$\sigma$ above the background at energies above 100 GeV during the first 2 yr of observation. The analysis of the expected frequency of the highest energy flares occurring in T Tauri stars is consistent with our estimate. In addition, we have determined the minimum energy of the flare that would produce $\gamma$-ray emission, which is $\sim 5 \times 10^{37}$ erg. This agreement becomes a hard observational constraint supporting previous hypotheses about rare flares as the origin of unidentified $\gamma$-ray sources in star-forming regions.

Authors:Jamie Holder for the VERITAS Collaboration

Abstract: The Be/X-ray binary system LS V +44 17 (RX J0440.9+4431) is a potential member of the rare class of gamma-ray binaries. The system is comprised of a Be star and a neutron star companion with an orbital period of 150 days. In December of 2022, MAXI detected an X-ray outburst from the source, which peaked in early January before declining and then re-brightening. During the second peak, the flux exceeded 1 Crab in the 15-50 keV range, and exhibited a pulsed emission component with a pulse period of 208 seconds. VERITAS observations were conducted close to the peak of the second outburst, from January 24 to January 27, 2023. We report here on the search for very high energy (VHE) gamma-ray emission in these data.

Authors:Marcin Marculewicz, Mouyuan Sun, Jianfeng Wu, Zhixiang Zhang

Abstract: The widely adopted ``lamppost'' thermal reprocessing model, in which the variable UV/optical emission is a result of the accretion disk reprocessing of the highly fluctuating X-ray emission, can be tested by measuring inter-band time lags in quasars spanning a range of X-ray power. This work reports the inter-band time lag in an apparently X-ray weak quasar, SDSS J153913.47+395423.4. A significant cross-correlation with a time delay of $\sim 33$ days (observed-frame) is detected in the Zwicky Transient Facility (ZTF) $g$ and $r$ light curves of SDSS J153913.47+395423.4. The observed X-ray power seems to be too weak to account for the observed inter-band cross-correlation with time delay. Hence the X-ray weak quasar SDSS J153913.47+395423.4 is either intrinsically X-ray normal (but observationally X-ray weak), or the X-ray emission is not the only mechanism to drive UV/optical variability. In the former case, the required X-ray power is at least 19 times stronger than observed, which requires either an exceptionally anisotropic corona or Compton-thick obscuration. Alternatively, the Corona-heated Accretion disk Reprocessing (CHAR) or the EUV torus models may account for the observed time lags.

Authors:Raj Prince, Anuvab Banerjee, Ajay Sharma, Avik Kumar das, Alok C. Gupta, Debanjan Bose

Abstract: We present a variability study of the blazar PKS 0346-27 from December 2018 to January 2022 in its archival $\gamma$-ray observation by Fermi-LAT. We use the Lomb-Scargle periodogram and the weighted wavelet transform methods in order to detect the presence of periodicity/quasi-periodicity and localize this feature in time and frequency space. The significance of the periodicity feature has been estimated using the Monte-Carlo simulation approach. We have also determined the global significance of the periodicity to test the robustness of our claim. To explore the most probable scenario, we modeled the light curve with both a straight jet and a curved jet model. We detect a periodicity feature of $\sim$ 100 days duration for the entire period of observation with a statistical significance of $3\sigma$, which amounts to a 99.7\% confidence level. The global significance of this feature is found to be 96.96\%. Based on the Akaike Information Criteria, the most probable explanation is that the observed emission is enhanced due to the helical motion of a blob within a curved jet. The origin of this QPO is very likely a region of enhanced emission moving helically inside a curved jet. This work presents strong evidence for jet curvature in the source and an independent (albeit a little serendipitous) procedure to estimate the curvature in blazar jets.

Authors:Jia-Chun He, Xiao-Na Sun, Jie-Shuang Wang, Frank M. Rieger, Ruo-Yu Liu, En-Wei Liang

Abstract: Shear particle acceleration is a promising candidate for the origin of extended high-energy emission in extra-galactic jets. In this paper, we explore the applicability of a shear model to 24 X-ray knots in the large-scale jets of FR II radio galaxies, and study the jet properties by modeling the multi-wavelength spectral energy distributions (SEDs) in a leptonic framework including synchrotron and inverse Compton - CMB processes. In order to improve spectral modelling, we analyze Fermi-LAT data for five sources and reanalyzed archival data of Chandra on 15 knots, exploring the radio to X-ray connection. We show that the X-ray SEDs of these knots can be satisfactorily modelled by synchrotron radiation from a second, shear-accelerated electron population reaching multi-TeV energies. The inferred flow speeds are compatible with large-scale jets being mildly relativistic. We explore two different shear flow profiles (i.e., linearly decreasing and power-law) and find that the required spine speeds differ only slightly, supporting the notion that for higher flow speeds the variations in particle spectral indices are less dependent on the presumed velocity profile. The derived magnetic field strengths are in the range of a few to ten microGauss, and the required power in non-thermal particles typically well below the Eddington constraint. Finally, the inferred parameters are used to constrain the potential of FR II jets as possible UHECR accelerators.

Authors:Rowan Batzofin University of Potsdam, Pierre Cristofari Observatoire de Paris PSL Research University, Kathrin Egberts University of Potsdam, Constantin Steppa University of Potsdam

Abstract: SNRs are likely to be significant sources of Galactic cosmic rays up to the knee. They produce gamma rays in the very-high-energy (E>100 GeV) range mainly via two mechanisms: hadronic interactions of accelerated protons with the interstellar medium and leptonic interactions of accelerated electrons with soft photons. Observations with current instruments have lead to the detection of about a dozen SNRs in VHE gamma rays and future instruments will help significantly increase this number. Yet, the details of particle acceleration at SNRs, and of the mechanisms producing VHE gamma-ray at SNRs remain poorly understood: What is the spectrum of accelerated particles? What is the efficiency of particle acceleration? Is the gamma-ray emission dominated by hadronic or leptonic origin? To address these questions, we simulate the population of SNRs in the gamma-ray domain, and confront it to the current population of TeV SNRs. This method allows us to investigate several crucial aspects of particle acceleration at SNRs, such as the level of magnetic field around SNR shocks or scanning the parameter space of the accelerated particles (spectral index, electron to proton ratio and the acceleration efficiency of the shock) with the possibility to constrain some of the parameters.

Authors:Israel Martinez-Castellanos, Savitri Gallego, Chien-You Huang, Chris Karwin, Carolyn Kierans, Jan Peter Lommler, Saurabh Mittal, Michela Negro, Eliza Neights, Sean N. Pike, Yong Sheng, Thomas Siegert, Hiroki Yoneda, Andreas Zoglauer, John A. Tomsick, Steven E. Boggs, Dieter Hartmann, Marco Ajello, Eric Burns, Chris Fryer, Alexander Lowell, Julien Malzac, Jarred Roberts, Pascal Saint-Hilaire, Albert Shih, Clio Sleator, Tadayuki Takahashi, Fabrizio Tavecchio, Eric Wulf, Jacqueline Beechert, Hannah Gulick, Alyson Joens, Hadar Lazar, Juan Carlos Martinez Oliveros, Shigeki Matsumoto, Tom Melia, Mark Amman, Dhruv Bal, Peter von Ballmoos, Hugh Bates, Markus Böttcher, Andrea Bulgarelli, Elisabetta Cavazzuti, Hsiang-Kuang Chang, Claire Chen, Che-Yen Chu, Alex Ciabattoni, Luigi Costamante, Lente Dreyer, Valentina Fioretti, Francesco Fenu, Giancarlo Ghirlanda, Eric Grove, Pierre Jean, Nikita Khatiya, Jürgen Knödlseder, Martin Krause, Mark Leising, Tiffany R. Lewis, Lea Marcotulli, Samer Al Nussirat, Kazuhiro Nakazawa, Uwe Oberlack, David Palmore, Gabriele Panebianco, Nicolo Parmiggiani, Tyler Parsotan, Field Rogers, Hester Schutte, Alan P. Smale, Jacob Smith, Aaron Trigg, Tonia Venters, Yu Watanabe, Haocheng Zhang

Abstract: The Compton Spectrometer and Imager (COSI) is a selected Small Explorer (SMEX) mission launching in 2027. It consists of a large field-of-view Compton telescope that will probe with increased sensitivity the under-explored MeV gamma-ray sky (0.2-5 MeV). We will present the current status of cosipy, a Python library that will perform spectral and polarization fits, image deconvolution, and all high-level analysis tasks required by COSI's broad science goals: uncovering the origin of the Galactic positrons, mapping the sites of Galactic nucleosynthesis, improving our models of the jet and emission mechanism of gamma-ray bursts (GRBs) and active galactic nuclei (AGNs), and detecting and localizing gravitational wave and neutrino sources. The cosipy library builds on the experience gained during the COSI balloon campaigns and will bring the analysis of data in the Compton regime to a modern open-source likelihood-based code, capable of performing coherent joint fits with other instruments using the Multi-Mission Maximum Likelihood framework (3ML). In this contribution, we will also discuss our plans to receive feedback from the community by having yearly software releases accompanied by publicly-available data challenges.

Authors:Niwano Masafumi, Murata L. Katsuhiro, Ito Naohiro, Yatsu Yoichi, Kawai Nobuyuki

Abstract: We analyzed optical/X-ray quasi-simultaneous light curves of Aql X-1, obtained by MAXI (Monitor of All-sky X-ray Image), ZTF (Zwicky Transient Facility) and LCO (Las Cumbres Observatory) in about 3.6 years from 2016, for understanding electromagnetic radiation mechanisms during its outbursts. As a result, we confirmed that 5 outbursts had detected in the epoch, and that 3 outbursts underwent the X-ray state transition across Low-Hard, In-Transition, and High-Soft state while remaining 2 outbursts stayed in the Low-Hard state. We found that the optical spectral energy distribution in the High-Soft state is consistent with a simplified irradiated disk model, and that the optical color/magnitude variation can be explained by variations in the X-ray luminosity and the disk geometrical thickness.

Authors:Hajime Sotani, Toru Kojo

Abstract: We examine the gravitational wave frequencies of the fundamental ($f$-) and 1st pressure ($p_1$-) modes excited in the neutron star models constructed with the quark-hadron crossover (QHC) type equations of state (EOS). We find that the $f$-mode frequencies with QHC EOS basically are smaller and the $p_1$-mode frequencies with QHC EOS are larger than those with hadronic EOS, focusing on the neutron star model with a fixed mass. We also find that the universality in the $f$-mode frequencies multiplied by the stellar mass as a function of the stellar compactness or as a function of the dimensionless tidal deformability, which is derived with various hadronic EOSs, can keep even with QHC EOS. That is, using these universal relations, one cannot distinguish QHC EOS from hadronic EOSs. Instead, using the relations one can extract the stellar radii whose evolution from low to high mass neutron stars can differentiate QHC from hadronic EOSs. On the other hand, we find that the $p_1$-mode frequencies multiplied by the stellar mass with QHC EOS significantly deviate in a certain mass range from the corresponding empirical relations derived with various hadronic EOSs, with which one may distinguish QHC EOS from hadronic EOSs.

Authors:Samuzal Barua, Oluwashina K. Adegoke, Ranjeev Misra, Pramod Pawar, V. Jithesh, Biman J. Medhi

Abstract: Correlated variability between coronal X-rays and disc optical/UV photons provides a very useful diagnostic of the interplay between the different regions around an active galactic nucleus (AGN) and how they interact. AGN that reveal strong X-ray reflection in their spectra should normally exhibit optical/UV to X-ray correlation consistent with reprocessing -- where the optical/UV emission lag behind the X-rays. While such correlated delay has been seen in some sources, it has been absent in others. \rm{Mrk~1044} is one such source that has been known to reveal strong X-ray reflection in its spectra. In our analysis of three long \textit{XMM-Newton} and several \textit{Swift} observations of the source, we found no strong evidence for correlation between its UV and X-ray lightcurves both on short and long time scales. Among other plausible causes for the non-detection, we posit that higher X-ray variability than UV and strong general relativistic effects close to the black hole may also be responsible. We also present results from the spectral analysis based on \textit{XMM-Newton} and \textit{NuSTAR} observations, which show the strong soft X-ray excess and iron K$\alpha$ line in the 0.3--50 keV spectrum that can be described by relativistic reflection.

Authors:Jun-Yi Shen, Yuan-Chuan Zou, A. M. Chen, Duan-Yuan Gao

Abstract: The tera-electronvolt (TeV) light curve of gamma-ray burst (GRB) 221009A shows an unprecedentedly rapid rise at the beginning epoch. This phenomenon could be due to the strong absorption of photons and electrons within the emitting region. As the external shock expands outwards and the radius increases, the volume of matter also increases, leading to a gradual decrease in the optical depth for TeV photons. We explore several possibilities for the physical origin of this peculiar behavior. We calculate the optical depth for TeV photons due to annihilation with lower energy photons in the external shock and scattering by electrons produced via cascading of the TeV emission. Even under aggressive assumptions, we find the optical depths for these processes are orders of magnitude too small to explain the observed light curve. Other sources of absorbers, such as electrons in the ejecta or external shock, also do not yield sufficient optical depths. Therefore, the origin of the early peculiar TeV light curve remains uncertain.

Authors:Runduo Liang, Zhengyan Liu, Lei Lei, Wen Zhao

Abstract: Mergers of binary neutron stars are multimessenger sources of gravitational waves that have an optical luminous counterpart, commonly referred to as 'kilonova'. Inspired by the detection of GW170817, intensive searches have been conducted during the LIGO/Virgo O3 run. However, despite these efforts, no verified kilonova was detected. In this work, we present a parameter constraint method based on non-detection of optical searching considering both GW skymap, limited sky coverage, cadence, limiting magnitudes and the probability of astrophysical origin. We use our method to place constraints on EoS of neutron star based on follow-up during O3 run and obtain $M_{\rm TOV} = 2.170^{+0.120}_{-0.108}\ M_{\odot}$ at 90\% confidence level with the combination of other observations. And we also take outlook for WFST targeting kilonova throughout the LIGO/Virgo O4 run. With more events handled, we will obtain more stringent constraints on EoS and kilonova populations.

Authors:Margot Boughelilba, Anita Reimer, Lukas Merten, Jon-Paul Lundquist

Abstract: In several jetted AGNs, structured jets have been observed. In particular spine-sheath configurations where the jet is radially divided into two or more zones of different flow velocities. We present a model based on the particle and radiation transport code CR-ENTREES. Here, interaction rates and secondary particle and photon yields are pre-calculated by Monte Carlo event generators or semi-analytical approximations. These are then used to create transition matrices, that describe how each particle spectrum evolves with time. This code allows for arbitrary injection of primary particles, and the possibility to choose which interaction to include (photo-meson production, Bethe-Heitler pair-production, inverse-Compton scattering, $\gamma$-$\gamma$ pair production, decay of all unstable particles, synchrotron radiation -- from electrons, protons, and all relevant secondaries before their respective decays -- and particle escape). In addition to the particle and radiation interactions taking place in each homogeneous zone, we implement the feedback between the two zones having different bulk velocities. The main mechanism at play when particles cross the boundary between the two zones is shear acceleration. We follow a microscopic description of this acceleration process to create a corresponding transition matrix and include it in our numerical setup. Furthermore, each zone's radiation field can be used as an external target photon field for the other zone's particle interactions. We present here the first results of the effect of a two-zone spine-sheath jet, by applying this model to typical low-luminosity AGNs.

Authors:Teresa Bister, Glennys Farrar

Abstract: We report on several new results using anisotropies of UHECRs. We improve and extend the work of Ding, Globus and Farrar, who modeled the UHECR dipole assuming sources follow the dark matter distribution, accounting for deflections in the Galactic and extragalactic magnetic fields but using a simplified treatment of interactions during propagation. The work presented here employs an accurate and self-consistent treatment of the evolution of composition during propagation, allows for and explores the impact of "bias" in the relation between UHECR sources and the dark matter distribution, and investigates the possible generation of arrival-direction-dependent composition anisotropies. Limits on the source number density consistent with the observed anisotropies are derived for the case where UHECR sources follow the dark matter distribution, and compared to a homogeneous source distribution case.

Authors:X. L. Miao, W. W. Zhu, M. Kramer, P. C. C. Freire, L. Shao, M. Yuan, L. Q. Meng, Z. W. Wu, C. C. Miao, Y. J. Guo, D. J. Champion, E. Fonseca, J. M. Yao, M. Y. Xue, J. R. Niu, H. Hu, C. M. Zhang

Abstract: In our work, we analyse $5\times10^{4}$ single pulses from the recycled pulsar PSR J2222$-$0137 in one of its scintillation maxima observed by the Five-hundred-meter Aperture Spherical radio Telescope (FAST). PSR J2222$-$0137 is one of the nearest and best studies of binary pulsars and a unique laboratory for testing gravitational theories. We report single pulses' energy distribution and polarization from the pulsar's main-pulse region. The single pulse energy follows the log-normal distribution. We resolve a steep polarization swing, but at the current time resolution ($64\,\mu{\rm s}$), we find no evidence for the orthogonal jump in the main-pulse region, as has been suspected. We find a potential sub-pulse drifting period of $P_{3} \sim 3.5\,P$. We analyse the jitter noise from different integrated numbers of pulses and find that its $\sigma_{j}$ is $270\pm{9}\,{\rm ns}$ for 1-hr integration at 1.25 GHz. This result is useful for optimizing future timing campaigns with FAST or other radio telescopes.

Authors:Yuki Takei, Tsuna Daichi, Takatoshi Ko, Toshikazu Shigeyama

Abstract: We present the updated open-source code Complete History of Interaction-Powered Supernovae (CHIPS) that can be applied to modeling supernovae (SNe) arising from an interaction with massive circumstellar medium (CSM) as well as the formation process of the CSM. Our update mainly concerns with extensions to hydrogen-poor SNe from stripped progenitors, targeting modeling of interaction-powered SNe Ibc such as Type Ibn and Icn SNe. We successfully reproduce the basic properties of the light curves of these types of SNe that occur after partial eruption of the outermost layer with a mass of $0.01$--$0.1\,M_\odot$ at $\lesssim 1$ year before explosion. We also find that the luminosity of the observed precursors can be naturally explained by the outburst that creates the dense CSM, given that the energy of the outburst is efficiently dissipated by collision with an external material, possibly generated by a previous mass eruption. We discuss possible scenarios causing eruptive mass-loss based on our results.

Authors:J. P. Lundquist, L. Merten, S. Vorobiov, M. Boughelilba, A. Reimer, P. Da Vela, F. Tavecchio, G. Bonnoli, C. Righi

Abstract: This study investigates low luminosity Fanaroff-Riley Type 0 (FR0) radio galaxies as a potentially significant source of ultra-high energy cosmic rays (UHECRs). Due to their much higher prevalence in the local universe compared to more powerful radio galaxies (about five times more than FR-1s), FR0s may provide a substantial fraction of the total UHECR energy density. To determine the nucleon composition and energy spectrum of UHECRs emitted by FR0 sources, simulation results from CRPropa3 are fit to Pierre Auger Observatory data. The resulting emission spectral indices, rigidity cutoffs, and nucleon fractions are compared to recent Auger results. The FR0 simulations include the approximately isotropic distribution of FR0 galaxies and various intergalactic magnetic field configurations (including random and structured fields) and predict the fluxes of secondary photons and neutrinos produced during UHECR propagation through cosmic photon backgrounds. This comprehensive simulation allows for investigating the properties of the FR0 sources using observational multi-messenger data.

Authors:Debatri Chattopadhyay, Jakob Stegmann, Fabio Antonini, Jordan Barber, Isobel M. Romero-Shaw

Abstract: We investigate the formation of intermediate mass black holes (IMBHs) through hierarchical mergers of stellar origin black holes (BHs), as well as BH mergers formed dynamically in nuclear star clusters. Using a semi-analytical approach which incorporates probabilistic mass-function-dependent double BH (DBH) pairing, binary-single encounters, and a mass-ratio-dependent prescription for energy dissipation in hardening binaries, we find that IMBHs with masses of $\mathcal{O}(10^2)$~--~$\mathcal{O}(10^4)\,\rm M_\odot$ can be formed solely through hierarchical mergers in timescales of a few $100$\,Myrs to a few\,Gyrs. Clusters with escape velocities $\gtrsim400$\,km\,s$^{-1}$ inevitably form high-mass IMBHs. The spin distribution of IMBHs with masses $\gtrsim 10^3M_\odot$ is strongly clustered at $\chi\sim 0.15$; while for lower masses, it at $\chi\sim 0.7$. Eccentric mergers are more frequent for equal-mass binaries containing first- and/or second-generation BHs. Metal-rich, young, dense clusters can produce up to $20\%$ of their DBH mergers with eccentricity $\geq0.1$ at $10\,\rm Hz$, and $\sim2$~--~$9\%$ of all in-cluster mergers can form at $>10$\,Hz. Nuclear star clusters are therefore promising environments for the formation of highly-eccentric DBH mergers, detectable with current gravitational-wave detectors. Clusters of extreme mass ($\sim10^8$\,M$_\odot$) and density ($\sim10^8$\,M$_\odot$pc$^{-3}$) can have about half of all of their DBH mergers with primary masses $\geq100$\,M$_\odot$. The fraction of in-cluster mergers increases rapidly with increasing cluster escape velocity, being nearly unity for $v_{\rm esc}\gtrsim 200$\,km\,s$^{-1}$. Cosmological merger rate of DBHs from nuclear clusters varies $\approx0.01-1$\,Gpc$^{-3}$yr$^{-1}$.

Authors:Vitaliy Kim, Ildana Izmailova, Yerlan Aimuratov

Abstract: A catalog of the Galactic population of X-ray pulsars in high-mass X-ray binary (HMXB) systems is presented. It contains information about 82 confirmed sources: 18 persistent and 64 transient pulsars. Their basic parameters include spin period, spin evolution with global and local spin-up/spin-down and duration, orbital period, X-ray luminosity, magnetic field strength measured by cyclotron line analysis, distance, spectral and luminosity class, observable parameters of massive companions, which are shown in the tables provided, with corresponding references. Candidates of the HMXB pulsars are also listed for further careful consideration.

Authors:Tuomo Salmi, Serena Vinciguerra, Devarshi Choudhury, Anna L. Watts, Wynn C. G. Ho, Sebastien Guillot, Yves Kini, Bas Dorsman, Sharon M. Morsink, Slavko Bogdanov

Abstract: We present an analysis of the effects of uncertainties in the atmosphere models on the radius, mass, and other neutron star parameter constraints for the NICER observations of rotation-powered millisecond pulsars. To date, NICER has applied the X-ray pulse profile modeling technique to two millisecond-period pulsars: PSR J0030+0451 and the high-mass pulsar PSR J0740+6620. These studies have commonly assumed a deep-heated fully-ionized hydrogen atmosphere model, although they have explored the effects of partial-ionization and helium composition in some cases. Here we extend that exploration and also include new models with partially ionized carbon composition, externally heated hydrogen, and an empirical atmospheric beaming parametrization to explore deviations in the expected anisotropy of the emitted radiation. None of the studied atmosphere cases have any significant influence on the inferred radius of PSR J0740+6620, possibly due to its X-ray faintness, tighter external constraints, and/or viewing geometry. In the case of PSR J0030+0451 both the composition and ionization state could significantly alter the inferred radius. However, based on the evidence (prior predictive probability of the data), partially ionized hydrogen and carbon atmospheres are disfavored. The difference in the evidence for ionized hydrogen and helium atmospheres is too small to be decisive for most cases, but the inferred radius for helium models trends to larger sizes around or above 14-15 km. External heating or deviations in the beaming that are less than $5\,\%$ at emission angles smaller than 60 degrees, on the other hand, have no significant effect on the inferred radius.

Authors:Aya Ishihara for the IceCube-Gen2 Collaboration

Abstract: The IceCube Neutrino Observatory, a cubic-kilometer-scale neutrino detector at the geographic South Pole, has reached a number of milestones in the field of neutrino astrophysics: the discovery of a high-energy astrophysical neutrino flux, the temporal and directional correlation of neutrinos with a flaring blazar, and a steady emission of neutrinos from the direction of an active galaxy of a Seyfert II type and the Milky Way. The next generation neutrino telescope, IceCube-Gen2, currently under development, will consist of three essential components: an array of about 10,000 optical sensors, embedded within approximately 8 cubic kilometers of ice, for detecting neutrinos with energies of TeV and above, with a sensitivity five times greater than that of IceCube; a surface array with scintillation panels and radio antennas targeting air showers; and buried radio antennas distributed over an area of more than 400 square kilometers to significantly enhance the sensitivity of detecting neutrino sources beyond EeV. This contribution describes the design and status of IceCube-Gen2 and discusses the expected sensitivity from the simulations of the optical, surface, and radio components.

Authors:Serena Vinciguerra, Tuomo Salmi, Anna L. Watts, Devarshi Choudhury, Thomas E. Riley, Paul S. Ray, Slavko Bogdanov, Yves Kini, Sebastien Guillot, Deepto Chakrabarty, Wynn C. G. Ho, Daniela Huppenkothen, Sharon M. Morsink, Zorawar Wadiasingh

Abstract: In 2019 the NICER collaboration published the first mass and radius inferred for PSR J0030+0451, thanks to NICER observations, and consequent constraints on the equation of state characterising dense matter. Two independent analyses found a mass of $\sim 1.3-1.4\,\mathrm{M_\odot}$ and a radius of $\sim 13\,$km. They also both found that the hot spots were all located on the same hemisphere, opposite to the observer, and that at least one of them had a significantly elongated shape. Here we reanalyse, in greater detail, the same NICER data set, incorporating the effects of an updated NICER response matrix and using an upgraded analysis framework. We expand the adopted models and jointly analyse also XMM-Newton data, which enables us to better constrain the fraction of observed counts coming from PSR J0030+0451. Adopting the same models used in previous publications, we find consistent results, although with more stringent inference requirements. We also find a multi-modal structure in the posterior surface. This becomes crucial when XMM-Newton data is accounted for. Including the corresponding constraints disfavors the main solutions found previously, in favor of the new and more complex models. These have inferred masses and radii of $\sim [1.4 \mathrm{M_\odot}, 11.5$ km] and $\sim [1.7 \mathrm{M_\odot}, 14.5$ km], depending on the assumed model. They display configurations that do not require the two hot spots generating the observed X-rays to be on the same hemisphere, nor to show very elongated features, and point instead to the presence of temperature gradients and the need to account for them.

Authors:Aaqib Manzoor, Sunder Sahayanathan, Zahir Shah, Subir Bhattacharyya, Naseer Iqbal, Zahoor Malik

Abstract: The availability of simultaneous X-ray and Very High Energy (VHE) observations of blazars helps to identify the plausible radiative contributors to the VHE emission. Under leptonic scenario, the VHE emission from BL Lacs are attributed to the synchrotron self Compton (SSC) emission. However, many BL Lacerate (BL Lacs) have shown significant hardening at VHE after correction for the Extra Galactic Background Light (EBL) attenuation. We study the spectral hardening of two nearby BL Lac objects, Mkn 421 and Mkn 501 having most number of simultaneous X-ray and VHE observations available among all the blazars. These BL Lacs are relatively close and the effect of EBL attenuation is relatively minimal/negligible. We study the scatter plot between the X-ray spectral indices and intrinsic VHE indices to identify the plausible origin of the VHE emission. For Mkn 501, the VHE spectral indices are steeper than X-ray spectra, suggesting the scattering process happening at extreme Klein-Nishina regime. On the other hand, for Mkn 421, the VHE spectra is remarkably harder than the X-ray spectra, which suggests an additional emission mechanism other than the SSC process. We show this hard VHE spectrum of Mkn 421 can be explained by considering the inverse Compton (IC) emission from a broken power law electron distribution with Maxwellian pileup. The possibility of the hadronic contribution at VHE {\gamma}-rays is also explored by modeling the hard spectrum under photomeson process.

Authors:Giancarlo Mattia, Luca Del Zanna, Matteo Bugli, Andrea Pavan, Riccardo Ciolfi, Gianluigi Bodo, Andrea Mignone

Abstract: Aims. The main goal of the present paper is to provide the first systematic numerical study of the propagation of astrophysical relativistic jets, in the context of high-resolution shock-capturing resistive relativistic magnetohydrodynamics (RRMHD) simulations. We aim at investigating different values and models for the plasma resistivity coefficient, and at assessing their impact on the level of turbulence, the formation of current sheets and reconnection plasmoids, the electromagnetic energy content, and the dissipated power. Methods. We use the PLUTO code for simulations and we assume an axisymmetric setup for jets, endowed with both poloidal and toroidal magnetic fields, and propagating in a uniform magnetized medium. The gas is assumed to be characterized by a realistic Synge-like equation of state (Taub equation), appropriate for such type of astrophysical jets. The Taub equation is combined here for the first time with the Implicit-Explicit Runge-Kutta time-stepping procedure, as required in RRMHD simulations. Results. The main result is that turbulence is clearly suppressed for the highest values of resistivity (low Lundquist numbers), current sheets are broader, and plasmoids are barely present, while for low values of resistivity results are very similar to ideal runs, where dissipation is purely numerical. We find that recipes employing a variable resistivity based on the advection of a jet tracer or on the assumption of a uniform Lundquist number improve on the use of a constant coefficient and are probably more realistic, preserving the development of turbulence and of sharp current sheets, possible sites for the acceleration of the non-thermal particles producing the observed high-energy emission.

Authors:Lukas Merten, Paolo Da Vela, Anita Reimer, Margot Boughelilba, Jon Paul Lundquist, Serguei Vorobiov, Julia Becker Tjus

Abstract: We present a new energy transport code that models the time dependent and non-linear evolution of spectra of cosmic-ray nuclei, their secondaries, and photon target fields. The software can inject an arbitrary chemical composition including heavy elements up to iron nuclei. Energy losses and secondary production due to interactions of cosmic ray nuclei, secondary mesons, leptons, or gamma-rays with a target photon field are available for all relevant processes, e.g., photo-meson production, photo disintegration, synchrotron radiation, Inverse Compton scattering, and more. The resulting x-ray fluxes can be fed back into the simulation chain to correct the initial photon targets, resulting in a non-linear treatment of the energy transport. The modular structure of the code facilitates simple extension of interaction or target field models. We will show how the software can be used to improve predictions of observables in various astrophysical sources such as jetted active galactic nuclei (AGN). Since the software can model the propagation of heavy ultrahigh-energy cosmic rays inside the source it can precisely predict the chemical composition at the source. This will also refine predictions of neutrino emissions - they strongly depend on the chemical composition. This helps in the future to optimize the selection and analyses of data from the IceCube neutrino observatory with the aim to enhance the sensitivity of IceCube and reduce the number of trial factors.

Authors:Sophie Aerdker, Rafael Alves Batista, Julia Becker Tjus, Julien Dörner, Andrej Dundovic, Björn Eichmann, Antonius Frie, Christopher Heiter, Mario Hoerbe, Karl-Heinz Kampert, Lukas Merten, Gero Müller, Patrick Reichherzer, Simone Rossoni, Andrey Saveliev, Leander Schlegel, Günter Sigl, Arjen van Vliet, Tobias Winchen

Abstract: CRPropa is a Monte Carlo framework for simulating the propagation of (ultra-) high-energy particles in the Universe, including cosmic rays, gamma rays, electrons, and neutrinos. It covers energies from ZeV down to GeV for gamma rays and electrons, and TeV for cosmic rays and neutrinos, supporting various astrophysical environments such as the surroundings of astrophysical sources, galactic, and extragalactic environments. The newest version, CRPropa 3.2, represents a significant leap forward towards a universal multi-messenger framework, opening up the possibility for many more astrophysical applications. This includes extensions to simulate cosmic-ray acceleration and particle interactions within astrophysical source environments, a full Monte Carlo treatment of electromagnetic cascades, improved ensemble-averaged Galactic propagation, significant performance improvements for cosmic-ray tracking through magnetic fields, and a user-friendly implementation of custom photon fields, among many more enhancements. This contribution will give an overview of the new features and present several applications to cosmic-ray and gamma-ray propagation.

Authors:Andre Sieverding MPI Astrophysik, Daniel Kresse MPI Astrophysik TUM Garching, Hans-Thomas Janka MPI Astrophysik

Abstract: The radioactive isotopes of 44Ti and 56Ni are important products of explosive nucleosynthesis, which play a key role for supernova (SN) diagnostics and were detected in several nearby young SN remnants. However, most SN models based on non-rotating single stars predict yields of 44Ti that are much lower than the values inferred from observations. We present, for the first time, the nucleosynthesis yields from a self-consistent three-dimensional (3D) SN simulation of an approximately 19 Msun progenitor star that reaches an explosion energy comparable to that of SN 1987A and that covers the evolution of the neutrino-driven explosion until more than 7 seconds after core bounce. We find a significant enhancement of the Ti/Fe yield compared to recent spherically symmetric (1D) models and demonstrate that the long-time evolution is crucial to understand the efficient production of 44Ti due to the non-monotonic temperature and density histories of ejected mass elements. Additionally, we identify characteristic signatures of the nucleosynthesis in proton-rich ejecta, in particular high yields of 45Sc and 64Zn.

Authors:William G. Thompson for the TAMBO Collaboration

Abstract: The detection of high-energy astrophysical neutrinos by IceCube has opened a new window on our Universe. While IceCube has measured the flux of these neutrinos at energies up to several PeV, much remains to be discovered regarding their origin and nature. Currently, measurements are limited by the small sample size of astrophysical neutrinos and by the difficulty of discriminating between electron and tau neutrinos. TAMBO is a next-generation neutrino observatory specifically designed to detect tau neutrinos in the 1-100 PeV energy range, enabling tests of neutrino physics at high energies and the characterization of astrophysical neutrino sources. The observatory will comprise an array of water Cherenkov and plastic scintillator detectors deployed on the face of the Colca Canyon in the Peruvian Andes. This unique geometry will facilitate a high-purity measurement of astrophysical tau neutrino properties. In this talk, I will present the prospects of TAMBO in the context of next-generation neutrino observatories and provide an overview of its current status.

Authors:Arghya Ranjan Das, Banibrata Mukhopadhyay

Abstract: Origin of wide varieties of quasi-periodic oscillation (QPO) observed in compact sources is still not well established. Its frequencies range from mHz to kHz spanning all compact objects. Are different QPOs, with different frequencies, originating from different Physics? We propose that the emergence of QPOs is the result of nonlinear resonance of fundamental modes present in accretion disks forced by external modes including that of the spin of the underlying compact object. Depending on the properties of accreting flow, e.g. its velocity and gradient, resonances, and any mode locking, take place at different frequencies, exhibiting low to high frequency QPOs. We explicitly demonstrate the origin of higher frequency QPOs for black holes and neutron stars by a unified model and outline how the same physics could be responsible to produce lower frequency QPOs. The model also predicts the spin of black holes, and constrains the radius of neutron stars and the mass of both.

Authors:Yuhan Yao, Wenbin Lu, Fiona Harrison, S. R. Kulkarni, Suvi Gezari, Muryel Guolo, S. Bradley Cenko, Anna Y. Q. Ho

Abstract: AT2022cmc was recently reported as the first on-axis jetted tidal disruption event (TDE) discovered in the last decade, and the fourth on-axis jetted TDE candidate known so far. In this work, we present NuSTAR hard X-ray (3--30 keV) observations of AT2022cmc, as well as soft X-ray (0.3--6 keV) observations obtained by NICER, Swift, and XMM-Newton. Our analysis reveals that the broadband X-ray spectra can be well described by a broken power-law with $f_\nu \propto \nu^{-0.5}$ ($f_\nu \propto \nu^{-1}$) below (above) the rest-frame break energy of $E_{\rm bk}\sim 10$ keV at observer-frame $t_{\rm obs}=7.8$ and 17.6 days since discovery. At $t_{\rm obs} = 36.2$ days, the X-ray spectrum is consistent with either a single power-law of $f_\nu \propto \nu^{-0.8}$ or a broken power-law with spectral slopes similar to the first two epochs. By modeling the spectral energy distribution evolution from radio to hard X-ray across the three NuSTAR observing epochs, we find that the sub-millimeter/radio emission originates from external shocks at large distances $\gtrsim\! 10^{17}$ cm from the black hole, the UV/optical light comes from a thermal envelope with radius $\sim\!10^{15}$ cm, and the X-ray emission is consistent with synchrotron radiation powered by energy dissipation at intermediate radii within the (likely magnetically dominated) jet. Our interpretation differs from the model proposed by Pasham et al. (2023) where both the radio and X-rays come from the same emitting zone in a matter-dominated jet. Our model for the jet X-ray emission has broad implications on the nature and radiation mechanism of relativistic jets in other sources such as gamma-ray bursts.

Authors:Shuta J. Tanaka, Kazumi Kashiyama

Abstract: Over three thousand pulsars have been discovered, but none have been confirmed to be younger than a few hundred years. Observing a pulsar after a supernova explosion will help us understand the properties of newborn ones, including their capability to produce gamma-ray bursts and fast radio bursts. Here, the possible youngest pulsar wind nebula (PWN) at the center of the SN 1986J remnant is studied. We demonstrate that the 5 GHz flux of 'PWN 1986J', increasing with time, is consistent with a stochastic acceleration model of PWNe developed to explain the flat radio spectrum of the Crab Nebula. We obtain an acceleration time-scale of electrons/positrons and a decay time-scale of the turbulence responsible for the stochastic acceleration as about 10 and 70 years, respectively. Our findings suggest that efficient stochastic acceleration and rising radio/submm light curves are characteristic signatures of the youngest PWNe. Follow-up ${\it ALMA}$ observations of decades-old supernovae within a few tens of Mpc, including SN 1986J, are encouraged to reveal the origin of the flat radio spectrum of PWNe.

Authors:Pei Wang, Jian Li, Long Ji, Xian Hou, Erbil Gugercinoglu, Di Li, Diego F. Torres, Yutong Chen, Jiarui Niu, Weiwei Zhu, Bing Zhang, En-wei Liang, Li Zhang, Mingyu Ge, Zigao Dai, Lin Lin, Jinlin Han, Yi Feng, Chenhui Niu, Yongkun Zhang, Dengjiang Zhou, Heng Xu, Chunfeng Zhang, Jinchen Jiang, Chenchen Miao, Mao Yuan, Weiyang Wang, Youling Yue, Yunsheng Wu, Yabiao Wang, Chengjie Wang, Zhenye Gan, Yuxi Li, Zhongyi Sun, Mingmin Chi

Abstract: Magnetars are neutron stars with extremely strong magnetic fields, frequently powering high-energy activity in X-rays. Pulsed radio emission following some X-ray outbursts have been detected, albeit its physical origin is unclear. It has long been speculated that the origin of magnetars' radio signals is different from those from canonical pulsars, although convincing evidence is still lacking. Five months after magnetar SGR 1935+2154's X-ray outburst and its associated Fast Radio Burst (FRB) 20200428, a radio pulsar phase was discovered. Here we report the discovery of X-ray spectral hardening associated with the emergence of periodic radio pulsations from SGR 1935+2154 and a detailed analysis of the properties of the radio pulses. The complex radio pulse morphology, which contains both narrow-band emission and frequency drifts, has not been seen before in other magnetars, but is similar to those of repeating FRBs - even though the luminosities are many orders of magnitude different. The observations suggest that radio emission originates from the outer magnetosphere of the magnetar, and the surface heating due to the bombardment of inward-going particles from the radio emission region is responsible for the observed X-ray spectral hardening.

Authors:Q. Remy

Abstract: The H.E.S.S. Galactic Plane Survey (HGPS), carried out between 2004 and 2013, is the most extensive survey of our Galaxy at very-high energies that covers the southern sky. Since the first HPGS catalogue release, the new observations accumulated provide a deeper scan of many Galactic sources, and a number of improvements have been made at various stages of the data processing chain, notably on events reconstruction and background modeling techniques. In parallel a new catalog production workflow has been tested and optimized on simulations done in preparation for the future Galactic Plane survey to be conducted by the Cherenkov Telescope Array (CTA). The development of a common data format and open scientific tools for gamma-ray astronomy allowed a smooth transition from the exploratory work done on CTA simulations to its application for H.E.S.S. data analysis. These elements offered a solid ground to build the second H.E.S.S. Galactic Plane Survey catalogue (2HGPS). In the following we will focus on the description of the catalogue workflow and show few results along the way.

Authors:Ramij Raja, Majidul Rahaman, Abhirup Datta, Oleg M. Smirnov

Abstract: Galaxy clusters are located at the nodes of cosmic filaments and therefore host a lot of hydrodynamical activity. However, cool core clusters are considered to be relatively relaxed systems without much merging activity. The Abell 85 cluster is a unique example where the cluster hosts both a cool core and multiple ongoing merging processes. In this work, we used 700 MHz uGMRT as well as MeerKAT L-band observations, carried out as part of the MGCLS, of the Abell 85. We reconfirm the presence of a minihalo in the cluster centre at 700MHz that was recently discovered in MGCLS. Furthermore, we discovered a radio bridge connecting the central minihalo and the peripheral radio phoenix. The mean surface brightness, size and flux density of the bridge at 700 MHz is found to be $\sim 0.14\ \mu$Jy/arcsec$^2$, $\sim 220$ kpc and $\sim 4.88$ mJy, respectively, with a spectral index of $\alpha_{700}^{1.28} = -0.92$. Although the origin of the seed relativistic electrons is still unknown, turbulent re-acceleration caused by both the spiralling sloshing gas in the intracluster medium (ICM) and the post-shock turbulence from the outgoing merging shock associated with the phoenix formation may be responsible for the bridge.

Authors:Anastasia Tsvetkova Dipartimento di Fisica, Universita degli Studi di Cagliari, SP Monserrato-Sestu, Monserrato, Italy Ioffe Institute, St. Petersburg, Russia, Luciano Burderi Dipartimento di Fisica, Universita degli Studi di Cagliari, SP Monserrato-Sestu, Monserrato, Italy INFN, Sezione di Cagliari, Cittadella Universitaria, Monserrato, CA, Italy INAF-Osservatorio Astronomico di Cagliari, Selargius, Alessandro Riggio Dipartimento di Fisica, Universita degli Studi di Cagliari, SP Monserrato-Sestu, Monserrato, Italy INFN, Sezione di Cagliari, Cittadella Universitaria, Monserrato, CA, Italy INAF-Istituto di Astrofisica Spaziale e Fisica Cosmica di Palermo, Palermo, Italy, Andrea Sanna Dipartimento di Fisica, Universita degli Studi di Cagliari, SP Monserrato-Sestu, Monserrato, Italy INFN, Sezione di Cagliari, Cittadella Universitaria, Monserrato, CA, Italy INAF-Osservatorio Astronomico di Cagliari, Selargius, Tiziana Di Salvo Dipartimento di Fisica e Chimica, Universita degli Studi di Palermo, Palermo, Italy

Abstract: According to Einstein's special relativity theory, the speed of light in a vacuum is constant for all observers. However, quantum gravity effects could introduce its dispersion depending on the energy of photons. The investigation of the spectral lags between the gamma-ray burst (GRB) light curves recorded in distinct energy ranges could shed light on this phenomenon: the lags could reflect the variation of the speed of light if it is linearly dependent on the photon energy and a function of the GRB redshift. We propose a methodology to start investigating the dispersion law of light propagation in a vacuum using GRB light curves. This technique is intended to be fully exploited using the GRB data collected with THESEUS.

Authors:Andrei P. Igoshev, Rainer Hollerbach, Toby Wood

Abstract: Off-centred dipole configurations have been suggested to explain different phenomena in neutron stars, such as natal kicks, irregularities in polarisation of radio pulsars and properties of X-ray emission from millisecond pulsars. Here for the first time we model magneto-thermal evolution of neutron stars with crust-confined magnetic fields and off-centred dipole moments. We find that the dipole shift decays with time if the initial configuration has no toroidal magnetic field. The decay timescale is inversely proportional to magnetic field. The octupole moment decreases much faster than the quadrupole. Alternatively, if the initial condition includes strong dipolar toroidal magnetic field, the external poloidal magnetic field evolves from centred dipole to off-centred dipole. The surface thermal maps are very different for configurations with weak $B = 10^{13}$ G and strong $B = 10^{14}$ G magnetic fields. In the former case, the magnetic equator is cold while in the latter case it is hot. We model lightcurves and spectra of our magneto-thermal configurations. We found that in the case of cold equator, the pulsed fraction is small (below a few percent in most cases) and spectra are well described with a single blackbody. Under the same conditions models with stronger magnetic fields produce lightcurves with pulsed fraction of tens of percent. Their spectra are significantly better described with two blackbodies. Overall, the magnetic field strength has a more significant effect on bulk thermal emission of neutron stars than does the field geometry.

Authors:Hao Wang, Paz Beniamini, Dimitrios Giannios

Abstract: Kilonovae are optical transients following the merger of neutron star binaries, which are powered by the r-process heating of merger ejecta. However, if a merger remnant is a long-living supramassive neutron star supported by its uniform rotation, it will inject energy into the ejecta through spindown power. The energy injection can boost the peak luminosity of a kilonova by many orders of magnitudes, thus significantly increasing the detectable volume. Therefore, even if such events are only a small fraction of the kilonovae population, they could dominate the detection rates. However, after many years of optical sky surveys, no such event has been confirmed. In this work, we build a boosted kilonova model with rich physical details, including the description of the evolution and stability of a proto neutron star, and the energy absorption through X-ray photoionization. We simulate the observation prospects and find the only way to match the absence of detection is to limit the energy injection by the newly born magnetar to only a small fraction of the neutron star rotational energy, thus they should collapse soon after the merger. Our result indicates that most supramassive neutron stars resulting from binary neutron star mergers are short lived and they must be rare in the universe.

Authors:Margret Westerkamp, Vincent Eberle, Matteo Guardiani, Philipp Frank, Lukas Platz, Philipp Arras, Jakob Knollmüller, Julia Stadler, Torsten Enßlin

Abstract: Supernovae are an important source of energy in the interstellar medium. Young remnants of supernovae have a peak emission in the X-ray region, making them interesting objects for X-ray observations. In particular, the supernova remnant SN1006 is of great interest due to its historical record, proximity and brightness. It has therefore been studied by several X-ray telescopes. Improving the X-ray imaging of this and other remnants is important but challenging as it requires to address a spatially varying instrument response in order to achieve a high signal-to-noise ratio. Here, we use Chandra observations to demonstrate the capabilities of Bayesian image reconstruction using information field theory. Our objective is to reconstruct denoised, deconvolved and spatio-spectral resolved images from X-ray observations and to decompose the emission into different morphologies, namely diffuse and point-like. Further, we aim to fuse data from different detectors and pointings into a mosaic and quantify the uncertainty of our result. Utilizing prior knowledge on the spatial and spectral correlation structure of the two components, diffuse emission and point sources, the presented method allows the effective decomposition of the signal into these. In order to accelerate the imaging process, we introduce a multi-step approach, in which the spatial reconstruction obtained for a single energy range is used to derive an informed starting point for the full spatio-spectral reconstruction. The method is applied to 11 Chandra observations of SN1006 from 2008 and 2012, providing a detailed, denoised and decomposed view of the remnant. In particular, the separated view of the diffuse emission should provide new insights into its complex small-scale structures in the center of the remnant and at the shock front profiles.

Authors:Philipp Fürst for the IceCube Collaboration

Abstract: The Ice Cube Neutrino Observatory has been measuring an isotropic astrophysical neutrino flux in multiple detection channels for almost a decade. Galactic diffuse emission, which arises from the interactions between cosmic rays and the interstellar medium, is an expected signal in IceCube. The superposition of an extragalactic flux and a galactic flux results in directional structure and variations in the spectrum. In this work, we use 12.3 years of high-purity muon-neutrino induced muon track data to perform a dedicated search for this galactic emission, combined with a spectral measurement of the isotropic astrophysical neutrino flux. To distinguish a galactic component from the dominant atmospheric and isotropic astrophysical components, the precise directional information available for muon tracks is fully utilized in a three-dimensional forward folding likelihood fit. We test a state-of-the-art model prediction of galactic diffuse emission based on recent cosmic ray data (CRINGE). We fit this prediction as a template scaled by a factor $\Psi_{\mathrm{CRINGE}}$, and find $2.9\pm 1.1 \times \Psi_{\mathrm{CRINGE}}$ with a significance of $2.7\sigma$ in an energy range between 400 GeV and 60 TeV in the Northern Sky.

Authors:Andrew Mummery, Sjoert van Velzen, Edward Nathan, Adam Ingram, Erica Hammerstein, Ludovic Fraser-Taliente, Steven Balbus

Abstract: We present fundamental scaling relationships between properties of the optical/UV light curves of tidal disruption events (TDEs) and the mass of the black hole that disrupted the star. We have uncovered these relations from the late-time emission of TDEs. Using a sample of 63 optically-selected TDEs, the latest catalog to date, we observed flattening of the early-time emission into a near-constant late-time plateau for at least two-thirds of our sources. Compared to other properties of the TDE lightcurves (e.g., peak luminosity or decay rate) the plateau luminosity shows the tightest correlation with the total mass of host galaxy ($p$-value of $2 \times 10^{-6}$, with a residual scatter of 0.3 dex). Physically this plateau stems from the presence of an accretion flow. We demonstrate theoretically and numerically that the amplitude of this plateau emission is strongly correlated with black hole mass. By simulating a large population of TDEs, we determine a plateau luminosity-black hole mass scaling relationship well described by $ \log_{10} \left(M_{\bullet}/M_{\odot} \right) = 1.50 \log_{10} \left( L_{\rm plat}/10^{43} {\rm erg \, s^{-1}} \right) + 9.0 $. The observed plateau luminosities of TDEs and black hole masses in our large sample are in excellent agreement with this simulation. Using the black hole mass predicted from the observed TDE plateau luminosity, we reproduce the well-known scaling relations between black hole mass and galaxy velocity dispersion. The large black hole masses of 10 of the TDEs in our sample allow us to provide constraints on their black hole spins, favouring rapidly rotating black holes. We add 49 (34) black hole masses to the galaxy mass (velocity dispersion) scaling relationships, updating and extending these correlations into the low black hole mass regime.

Authors:B. Müller Monash University

Abstract: Fallback in core-collapse supernova explosions is potentially of significant importance for the birth spins of neutron stars and black holes. It has recently been pointed out that the angular momentum imparted onto a compact remnant by fallback material is subtly intertwined with its kick because fallback onto a moving neutron star or black hole will preferentially come for a conical region around its direction of travel. We show that contrary to earlier expectations such one-sided fallback accretion onto a neutron star will tend to produce spin-kick misalignment. Since the baroclinic driving term in the vorticity equation is perpendicular to the nearly radial pressure gradient, convective eddies in the progenitor as well as Rayleigh-Taylor plumes growing during the explosion primarily carry angular momentum perpendicular to the radial direction. Fallback material from the accretion volume of a moving neutron star therefore carries substantial angular momentum perpendicular to the kick velocity. We estimate the seed angular momentum fluctuations from convective motions in core-collapse supernova progenitors and argue that accreted fallback material will almost invariably be accreted with the maximum permissible specific angular momentum for reaching the Alfv\'en radius. This imposes a limit of $\mathord{\sim}10^{-2}M_\odot$ of fallback accretion for fast-spinning young neutron stars with periods of $\mathord{\sim}20\,\mathrm{ms}$ and less for longer birth spin periods.

Authors:Serena Vinciguerra, Tuomo Salmi, Anna L. Watts, Devarshi Choudhury, Yves Kini, Thomas E. Riley

Abstract: In the last few years, the NICER collaboration has provided mass and radius inferences, via pulse profile modeling, for two pulsars: PSR J0030+0451 and PSR J0740+6620. Given the importance of these results for constraining the equation of state of dense nuclear matter, it is crucial to validate them and test their robustness. We therefore explore the reliability of these results and their sensitivity to analysis settings and random processes, including noise, focusing on the specific case of PSR J0030+0451. We use X-PSI, one of the two main analysis pipelines currently employed by the NICER collaboration for mass and radius inferences. With synthetic data that mimic the PSR J0030+0451 NICER data set, we evaluate the recovery performances of X-PSI under conditions never tested before, including complex modeling of the thermally emitting neutron star surface. For the test cases explored, our results suggest that X-PSI is capable of recovering the true mass and radius within reasonable credible intervals. This work also reveals the main vulnerabilities of the analysis: a significant dependence on noise and the presence of multi-modal structure in the posterior surface. Noise particularly impacts our sensitivity to the analysis settings and widths of the posterior distributions. The multi-modal structure in the posterior suggests that biases could be present if the analysis is unable to exhaustively explore the parameter space. Convergence testing, to ensure an adequate coverage of the parameter space and a suitable representation of the posterior distribution, is one possible solution to these challenges.

Authors:Charlotte Benning for the IceCube-Gen2 Collaboration, Jürgen Borowka for the IceCube-Gen2 Collaboration, Christoph Günther for the IceCube-Gen2 Collaboration, Oliver Gries for the IceCube-Gen2 Collaboration, Simon Zierke for the IceCube-Gen2 Collaboration

Abstract: The IceCube Upgrade will augment the existing IceCube Neutrino Observatory by deploying 700 additional optical sensor modules and calibration devices within its center at a depth of 1.5 to 2.5 km in the Antarctic ice. One goal of the Upgrade is to improve the positioning calibration of the optical sensors to increase the angular resolution for neutrino directional reconstruction. An acoustic calibration system will be deployed to explore the capability of achieving this using trilateration of propagation times of acoustic signals. Ten Acoustic Modules (AM) capable of sending and receiving acoustic signals with frequencies from 5 to 30 kHz will be installed within the detector volume. Additionally, compact acoustic sensors inside 15 optical sensor modules will complement the acoustic calibration system. With this system, we aim for an accuracy of a few tens of cm to localize the Acoustic Modules and sensors. Due to the longer attenuation length of sound compared to light within the ice, acoustic position calibration is especially interesting for the upcoming IceCube-Gen2 detector, which will have a string spacing of around 240 m. In this contribution we present an overview of the technical design of the Acoustic Module as well as results of performance tests with a first complete prototype.

Authors:M. Pohl for the VERITAS collaboration, the H.E.S.S. collaboration, K. Mori

Abstract: We report on multiwavelength target-of-opportunity observations of the blazar PKS 0735+178, located 2.2 degrees away from the best-fit position of the IceCube neutrino event 211208A. The source was in a high-flux state in the optical, ultraviolet, X-ray, and GeV gamma-ray bands around the time of the neutrino event, exhibiting daily variability in the soft X-ray flux. The X-ray data from Swift-XRT and NuSTAR characterize the transition between the low-energy and high-energy components of the broadband spectral energy distribution, and the gamma-ray data from Fermi-LAT, VERITAS, and H.E.S.S. require a spectral cut-off near 100 GeV. Both measurements provide strong constraints on leptonic and hadronic models. We analytically explore a synchrotron self-Compton model, an external Compton model, and a lepto-hadronic model. Models that are entirely based on internal photon fields face serious difficulties in matching the observed spectral energy distribution (SED). The existence of an external photon field in the source would instead explain the observed gamma-ray spectral cut-off in both leptonic and lepto-hadronic models, and it would allow a proton jet power that marginally agrees with the Eddington limit in the lepto-hadronic model. A numerical lepto-hadronic model with external target photons reproduces the observed SED and is reasonably consistent with the neutrino event despite requiring a high jet power.

Authors:Maximilian Meier for the IceCube Collaboration, Brian Clark for the IceCube Collaboration

Abstract: Extremely high energy (EHE) neutrinos (with energies above $10^7$ GeV) are produced in interactions of the highest energy cosmic rays. A primary contribution to the EHE neutrino flux is expected from so-called cosmogenic neutrinos produced when ultra high energy cosmic rays interact with ambient photon backgrounds. Observations of these EHE neutrinos with IceCube can probe the nature of cosmic rays beyond the energies for resonant photo-pion production (GZK cutoff). We present a new event selection of extremely high energy neutrinos by more effectively identifying and rejecting high multiplicity muon bundles with respect to previous analyses. Furthermore, we show the expected improvements of the quasi-differential upper limits on the EHE neutrino flux using 12 years of IceCube data.

Authors:Zhengli Wang Guangxi Key Laboratory for Relativistic Astrophysics, School of Physical Science and Technology, Guangxi University, Nanning 530004, China, Jiguang Lu National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China, Jinchen Jiang National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China, Shunshun Cao Department of Astronomy, School of Physics, Peking University, Beijing 100871, China, Kejia Lee Department of Astronomy, School of Physics, Peking University, Beijing 100871, China Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, China, Enwei Liang Guangxi Key Laboratory for Relativistic Astrophysics, School of Physical Science and Technology, Guangxi University, Nanning 530004, China, Lunhua Shang Guizhou Normal University, Guiyang 550025, China, Renxin Xu Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, China, Weiwei Zhu National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China

Abstract: The nearby radio pulsar B0950$+$08 with full duty cycle is targeted by the Five-hundred-meter Aperture Spherical radio Telescope (FAST, 110 minutes allocated), via adopting polarization calibration on two ways of baseline determination, in order to understand its magnetospheric radiation geometry as well as the polar cap sparking. % The radiation of the main pulse could not be informative of magnetic field line planes due to its low linear polarization ($<10 \%$) and the position angle jumps, and the polarization position angle in the pulse longitudes whose linear fractions are larger than $ \sim 30 \%$ is thus fitted in the classical rotating vector model (RVM). % The best RVM fit indicates that the inclination angle, $\alpha$, and the impact angle, $\beta$, of this pulsar are $100.5^{\circ}$ and $-33.2^{\circ}$, respectively, suggesting that the radio emission comes from two poles. % Polar cap sparking in the vacuum gap model, either the annular gap or the core gap, is therefore investigated in this RVM geometry, resulting in a high-altitude magnetospheric emission at heights from $\sim 0.25R_{\rm LC}$ to $\sim 0.56R_{\rm LC}$, with $R_{\rm LC}$ the light cylinder radius. % It is evident that both sparking points of the main and inter pulses are located mainly away from the magnetic pole, that is meaningful in the physics of pulsar surface and is even relevant to pulsar's inner structure.

Authors:Norman Khan, Matthew. J. Middleton

Abstract: The focus of NASA's Swift telescope has been transients and target-of-opportunity observing, resulting in many observations of ultraluminous X-ray sources (ULXs) over the last ~20 years. For the vast majority of these observations, simultaneous data has been obtained using both the X-ray telescope (XRT) and the ultraviolet and optical telescope (UVOT), providing a unique opportunity to study coupled variability between these bands. Using a sample of ~40 ULXs with numerous repeat observations, we extract stacked images to characterise the spatial extent of the UV-Optical emission and extract long-term light curves to search for first-order linear correlations between the UV and X-ray emission. We find that a small subset may show weakly correlated joint variability, while other sources appear to display non-linear relationships between the bands. We discuss these observations in the context of several theoretical models: precession, irradiation of the outer accretion disc and irradiation of the companion star. We conclude that more complicated analysis or higher quality data may be required to accurately constrain the nature of the joint X-ray and UV/optical emission in these sources.

Authors:Victor B. Valera, Mauricio Bustamante, Olga Mena

Abstract: Soon, a new generation of neutrino telescopes, presently under planning, will target the discovery of ultra-high-energy (UHE) neutrinos of cosmic origin, with energies higher than 100 PeV, that promise unique insight into astrophysics and particle physics. Yet, predictions of the UHE neutrino flux and interaction cross section -- whose measurement is co-dependent -- are laden with significant uncertainty that, if unaddressed, could misrepresent the capabilities to measure one or the other. To address this, we advocate for the joint measurement of the UHE neutrino spectrum and neutrino-nucleon cross section, including of their energy dependence, without assuming prior knowledge of either. We illustrate our methods by adopting empirical parametrizations of the neutrino spectrum, in forecasts geared to the planned radio array of the IceCube-Gen2 neutrino telescope. We warn against using simple parametrizations -- a simple power law or one augmented with an exponential cut-off -- that might fail to capture features of the spectrum that are commonplace in the predictions. We argue instead for the use of flexible parametrizations -- a piecewise power law or an interpolating polynomial -- that ensure accuracy. We report loose design targets for the detector energy and angular resolution that are compatible with those under present consideration.

Authors:Gopal Bhatta, Staszek Zola, M. Drozdz, Daniel Reichart, Joshua Haislip, Vladimir Kouprianov, Katsura Matsumoto, Eda Sonbas, D. Caton, Urszula Pajdosz-Śmierciak, A. Simon, J. Provencal, Dariusz Góra, Grzegorz Stachowski

Abstract: Intense outbursts in blazars are among the most extreme phenomena seen in extragalactic objects. Studying these events can offer important information about the energetic physical processes taking place within the innermost regions of blazars, which are beyond the resolution of current instruments. This work presents some of the largest and most rapid flares detected in the optical band from the sources 3C 279, OJ 49, S4 0954+658, Ton 599, and PG 1553+113, which are mostly TeV blazars. The source flux increased by nearly ten times within a few weeks, indicating the violent nature of these events. Such energetic events might originate from magnetohydrodynamical instabilities near the base of the jets, triggered by processes modulated by the magnetic field of the accretion disc. We explain the emergence of flares owing to the injection of high-energy particles by the shock wave passing along the relativistic jets. Alternatively, the flares may have also arisen due to geometrical effects related to the jets. We discuss both source-intrinsic and source-extrinsic scenarios as possible explanations for the observed large amplitude flux changes.

Authors:R. L. Becerra, A. Klotz, J. L. Atteia, D. Guetta, A. M. Watson, F. De Colle, C. Angulo-Valdez, N. R. Butler, S. Dichiara, N. Fraija, K. Garcia-Cifuentes, A. S. Kutyrev, W. H. Lee, M. Pereyra, E. Troja

Abstract: We collected the optical light curve data of 227 gamma-ray bursts (GRBs) observed with the TAROT, COATLI, and RATIR telescopes. These consist of 133 detections and 94 upper limits. We constructed average light curves in the observer and rest frames in both X-rays (from {\itshape Swift}/XRT) and in the optical. Our analysis focused on investigating the observational and intrinsic properties of GRBs. Specifically, we examined observational properties, such as the optical brightness function of the GRBs at $T=1000$ seconds after the trigger, as well as the temporal slope of the afterglow. We also estimated the redshift distribution for the GRBs within our sample. Of the 227 GRBs analysed, we found that 116 had a measured redshift. Based on these data, we calculated a local rate of $\rho_0=0.2$ Gpc$^{-3}$ yr$^{-1}$ for these events with $z<1$. To explore the intrinsic properties of GRBs, we examined the average X-ray and optical light curves in the rest frame. We use the {\scshape afterglowpy} library to generate synthetic curves to constrain the parameters typical of the bright GRB jet, such as energy (${\langle} {E_{0}}{\rangle}\sim 10^{53.6}$~erg), opening angle (${\langle}\theta_\mathrm{core}{\rangle}\sim 0.2$~rad), and density (${\langle}n_\mathrm{0}{\rangle}\sim10^{-2.1}$ cm$^{-3}$). Furthermore, we analyse microphysical parameters, including the fraction of thermal energy in accelerated electrons (${\langle}\epsilon_e{\rangle}\sim 10^{-1.37}$) and in the magnetic field (${\langle}\epsilon_B{\rangle}\sim10^{-2.26}$), and the power-law index of the population of non-thermal electrons (${\langle}p{\rangle}\sim 2.2$).

Authors:Neal Titus Thomas, S. B. Gudennavar, S. G. Bubbly

Abstract: We have studied the spectro-temporal properties of the neutron star low mass X-ray binary GX 9$+$1 using data from \textit{NuSTAR/FPM} and \textit{AstroSat/SXT} and \textit{LAXPC}. The hardness-intensity diagram of the source showed it to be in the soft spectral state during both observations. \textit{NuSTAR} spectral analysis yielded an inclination angle ($\theta$) $=$ 29$\substack{+3\\-4}^{\circ}$ and inner disk radius ($R_{in}$) $\leq$ 19.01 km. Assuming that the accretion disk was truncated at the Alfv\'en radius during the observation, the upper limit of the magnetic dipole moment ($\mu$) and the magnetic field strength ($B$) at the poles of the neutron star in GX 9$+$1 were calculated to be 1.45$\times$$10^{26}$ G cm$^3$ and 2.08$\times$$10^8$ G, respectively (for $k_A$ $=$ 1). Flux resolved spectral analysis with \textit{AstroSat} data showed the source to be in the soft spectral state ($F_{disk}$/$F_{total}$ $\sim$0.9) with a monotonic increase in mass accretion rate ($\dot{m}$) along the banana branch. The analysis also showed the presence of absorption edges at $\sim$1.9 and $\sim$2.4 keV, likely due to Si XIII and S XV, respectively. Temporal analysis with \textit{LAXPC-20} data in the 0.02 $-$ 100 Hz range revealed the presence of noise components, which could be characterized with broad Lorentzian components.

Authors:Hebzibha Isravel, Damien Begue, Asaf Pe'er

Abstract: Observations of long duration gamma-ray bursts (GRBs) with TeV emission during their afterglow have been on the rise. Recently, GRB 221009A, the most energetic GRB ever observed, was detected by the {LHAASO} experiment in the energy band 0.2 - 7 TeV. Here, we interpret its afterglow in the context of a hybrid model in which the TeV spectral component is explained by the proton-synchrotron process while the low energy emission from optical to X-ray is due to synchrotron radiation from electrons. We constrained the model parameters using the observed optical, X-ray and TeV data. By comparing the parameters of this burst and of GRB 190114C, we deduce that the VHE emission at energies $\geq$ 1 TeV in the GRB afterglow requires large explosion kinetic energy, $E \gtrsim 10^{54}$~erg and a reasonable circumburst density, $n\gtrsim 10$~cm$^{-3}$. This results in a small injection fractions of particles accelerated to a power-law, $\sim 10^{-2}$. {A significant fraction of shock energy must be allocated to a near equipartition magnetic field, $\epsilon_B \sim 10^{-1}$, while electrons should only carry a small fraction of this energy, $\epsilon_e \sim 10^{-3}$. Under these conditions required for a proton synchrotron model, namely $\epsilon_B \gg \epsilon_e$, the SSC component is substantially sub-dominant over proton-synchrotron as a source of TeV photons.} These results lead us to suggest that proton-synchrotron process is a strong contender for the radiative mechanisms explaining GRB afterglows in the TeV band.

Authors:Nazma Husain, Akash Garg, Ranjeev Misra, Somasri Sen

Abstract: Black hole X-ray binaries routinely exhibit Quasi Periodic Oscillations (QPOs) in their Power density spectrum. Studies of QPOs have demonstrated immense ability to understand these dynamical systems although their unambiguous origin still remains a challenge. We investigate the energy-dependent properties of the Type-C QPOs detected for H 1743-322 as observed with AstroSat in its two X-ray outbursts of 2016 and 2017. The combined broadband LAXPC and SXT spectrum is well modelled with a soft thermal and a hard Comptonization component. The QPO exhibits soft/negative lags i.e. variation in soft band lags the variation in hard band, although the upper harmonic shows opposite behaviour i.e. hard/positive lags. Here, we model energy-dependent properties (fractional root mean square and time-lag variation with energy) of the QPO and its upper harmonic individually with a general scheme that fits these properties by utilizing the spectral information and consequently allows to identify the radiative component responsible for producing the variability. Considering the truncated disk picture of accretion flow, a simple model with variation in inner disk temperature, heating rate and fractional scattering with time delays is able to describe the fractional RMS and time-lag spectra. In this work, we show that this technique can successfully describe the energy-dependent features and identify the spectral parameters generating the variability.

Authors:Alexander Sandrock for the CORSIKA 8 collaboration, Jean-Marco Alameddine for the CORSIKA 8 collaboration, Felix Riehn for the CORSIKA 8 collaboration

Abstract: The air shower simulation code CORSIKA has served as a key part of the simulation chain for numerous astroparticle physics experiments over the past decades. Due to retirement of the original developers and the increasingly difficult maintenance of the monolithic Fortran code of CORSIKA, a new air shower simulation framework has been developed over the course of the last years in C++, called CORSIKA 8. Besides the hadronic and muonic component, the electromagnetic component is one of the key constituents of an air shower. The cascade producing the electromagnetic component of an air shower is driven by bremsstrahlung and photoproduction of electron-positron pairs. At ultrahigh energies or in media with high densities, the bremsstrahlung and pair production processes are suppressed by the Landau-Pomeranchuk-Migdal (LPM) effect, which leads to more elongated showers compared to showers without the LPM suppression. Furthermore, photons at higher energies can produce muon pairs or interact hadronically with nucleons in the target medium, producing a muon component in electromagnetic air showers. In this contribution, we compare electromagnetic showers simulated with the latest Fortran version of CORSIKA and CORSIKA 8, which uses the library PROPOSAL for the electromagnetic component. While earlier validations of CORSIKA 8 electromagnetic showers focused on showers of lower energy, the recent implementation of the LPM effect, photo pair production of muons, and of photohadronic interactions allows now to make a physics-complete comparison also at high energies.

Authors:Mattias Ergon, Peter Lundqvist, Claes Fransson, Hanindyo Kuncarayakti, Kaustav K. Das, Kishalay De, Lucia Ferrari, Christoffer Fremling, Kyle Medler, Keiichi Maeda, Andrea Pastorello, Jesper Sollerman, Maximilian D. Stritzinger

Abstract: We use the light curve and spectral synthesis code JEKYLL to calculate a set of macroscopically mixed Type IIb supernova (SN) models, which are compared to both previously published and new late-phase observations of SN 2020acat. The models differ in the initial mass, the radial mixing and expansion of the radioactive material, and the properties of the hydrogen envelope. The best match to the photospheric and nebular spectra and lightcurves of SN 2020acat is found for a model with an initial mass of 17 solar masses, strong radial mixing and expansion of the radioactive material, and a 0.1 solar mass hydrogen envelope with a low hydrogen mass-fraction of 0.27. The most interesting result is that strong expansion of the clumps containing radioactive material seems to be required to fit the observations of SN 2020acat both in the diffusion phase and the nebular phase. These "Ni bubbles" are expected to expand due to heating from radioactive decays, but the degree of expansion is poorly constrained. Without strong expansion there is a tension between the diffusion phase and the subsequent evolution, and models that fit the nebular phase produce a diffusion peak that is too broad. The diffusion phase lightcurve is sensitive to the expansion of the "Ni bubbles", as the resulting Swiss-cheese-like geometry decreases the effective opacity and therefore the diffusion time. This effect has not been taken into account in previous lightcurve modelling of stripped-envelope SNe, which may lead to a systematic underestimate of their ejecta masses. It should be emphasized, though, that JEKYLL is limited to a geometry that is spherically symmetric on average, and large-scale asymmetries may also play a role. The relatively high initial mass found for the progenitor of SN 2020acat places it at the upper end of the mass distribution of Type IIb SN progenitors, and a single star origin can not be excluded.

Authors:Marco Stein Muzio, Luis A. Anchordoqui, Michael Unger

Abstract: One of the most challenging open questions regarding the origin of ultrahigh energy cosmic rays (UHECRs) deals with the shape of the source emission spectra. A commonly-used simplifying assumption is that the source spectra of the highest energy cosmic rays trace a Peters cycle, in which the maximum cosmic-ray energy scales linearly with $Z$, i.e., with the charge of the UHECR in units of the proton charge. However, this would only be a natural assumption for models in which UHECRs escape the acceleration region without suffering significant energy losses. In most cases, however, UHECRs interact in the acceleration region and/or in the source environment changing the shape of the source emission spectra. Energy losses are typically parameterized in terms of $Z$ and the UHECR baryon number $A$, and therefore one would expect the source emission spectra to be a function of both $Z$ and $A$. Taking a pragmatic approach, we investigate whether existing data favor any region of the $(Z,A)$ parameter space. Using data from the Pierre Auger Observatory, we carry out a maximum likelihood analysis of the observed spectrum and nuclear composition to shape the source emission spectra for the various particle species. We also study the impact of possible systematic uncertainties driven by hadronic models describing interactions in the atmosphere.

Authors:Marco Stein Muzio, Noémie Globus

Abstract: We present the extent to which anisotropies in the ultrahigh energy neutrino sky can probe the distribution of extreme astrophysical accelerators in the universe. In this talk, we discuss the origin of an anisotropic neutrino sky and show how observers can use this anisotropy to measure the evolution of ultrahigh energy neutrino sources - and therefore, the sources of ultrahigh energy cosmic rays - for the very first time.

Authors:Marco Stein Muzio for the RNO-G Collaboration

Abstract: The Radio Neutrino Observatory in Greenland (RNO-G) is the only ultrahigh energy (UHE, ${\gtrsim}30$~PeV) neutrino monitor of the Northern sky and will soon be the world's most sensitive high-uptime detector of UHE neutrinos. Because of this, RNO-G represents an important piece of the multimessenger landscape over the next decade. In this talk, we will highlight RNO-G's multimessenger capabilities and its potential to provide key information in the search for the most extreme astrophysical accelerators. In particular, we will highlight opportunities enabled by RNO-G's unique field-of-view, its potential to constrain the sources of UHE cosmic rays, and its complementarity with IceCube at lower energies.

Authors:Ryota Tomaru, Chris Done, Hirokazu Odaka

Abstract: New X-ray polarisation results are challenging our understanding of the accretion flow geometry in black hole binary systems. Even spectra dominated by a standard disc can give unexpected results, such as the high inclination black hole binary 4U 1630- 472, where the observed X-ray polarisation is much higher than predicted. This system also shows a strong, highly ionised wind, consistent with thermal-radiative driving from the outer disc, leading to speculation that scattering in the wind is responsible for the unexpectedly high polarisation degree from a standard optically thick disk. Here we show that this is not the case. The optically thin(ish) wind polarises the scattered light in a direction orthogonal to that predicted from a standard optically thick disc, reducing about 2% rather than enhancing the predicted polarisation of the total emission. This value is consistent with the polarisation difference between the disc-dominated soft state, where absorption lines by the wind are clearly seen, and the steep power-law state, where no absorption lines are seen. If this difference is genuinely due to the presence or absence of wind, the total polarisation direction must be orthogonal to the disc plane rather than parallel as expected from optically thick material.

Authors:Brian Hsu, Peter K. Blanchard, Edo Berger, Sebastian Gomez

Abstract: We present an extensive $\textit{Hubble Space Telescope}$ ($\textit{HST}$) rest-frame ultraviolet (UV) imaging study of the locations of Type I superluminous supernovae (SLSNe) within their host galaxies. The sample includes 65 SLSNe with detected host galaxies in the redshift range $z\approx 0.05-2$. Using precise astrometric matching with SN images, we determine the distributions of physical and host-normalized offsets relative to the host centers, as well as the fractional flux distribution relative to the underlying UV light distribution. We find that the host-normalized offsets of SLSNe roughly track an exponential disk profile, but exhibit an overabundance of sources with large offsets of $1.5-4$ times their host half-light radius. The SLSNe normalized offsets are systematically larger than those of long gamma-ray bursts (LGRBs), and even Type Ib/c and II SNe. Furthermore, we find that about 40\% of all SLSNe occur in the dimmest regions of their host galaxies (fractional flux of 0), in stark contrast to LGRBs and Type Ib/c and II SNe. We do not detect any significant trends in the locations of SLSNe as a function of redshift, or as a function of explosion and magnetar engine parameters inferred from modeling of their optical lights curves. The significant difference in SLSN locations compared to LGRBs (and normal core-collapse SNe) suggests that at least some of their progenitors follow a different evolutionary path. We speculate that SLSNe arise from massive runaway stars from disrupted binary systems, with velocities of $\sim 10^2$ km s$^{-1}$.

Authors:Shubham Srivastav, T. Moore, M. Nicholl, M. R. Magee, S. J. Smartt, M. D. Fulton, S. A. Sim, J. M. Pollin, L. Galbany, C. Inserra, A. Kozyreva, Takashi J. Moriya, F. P. Callan, X. Sheng, K. W. Smith, J. S. Sommer, J. P. Anderson, M. Deckers, M. Gromadzki, T. E. Müller-Bravo, G. Pignata, A. Rest, D. R. Young

Abstract: We present optical photometric and spectroscopic observations of the 02es-like type Ia supernova (SN) 2022ywc. The transient occurred in the outskirts of an elliptical host galaxy and showed a striking double-peaked light curve with an early excess feature detected in the ATLAS orange and cyan bands. The early excess is remarkably luminous with an absolute magnitude $\sim -19$, comparable in luminosity to the subsequent radioactively-driven second peak. The spectra resemble the hybrid 02es-like SN 2016jhr, that is considered to be a helium shell detonation candidate. We investigate different physical mechanisms that could power such a prominent early excess and rule out massive helium shell detonation, surface $^{56}$Ni distribution and ejecta-companion interaction. We conclude that SN ejecta interacting with circumstellar material (CSM) is the most viable scenario. Semi-analytical modelling with MOSFiT indicates that SN ejecta interacting with $\sim 0.05\,$M$_{\odot}$ of CSM at a distance of $\sim 10^{14}$ cm can explain the extraordinary light curve. A double-degenerate scenario may explain the origin of the CSM, either by tidally-stripped material from the secondary white dwarf, or disk-originated matter launched along polar axes following the disruption and accretion of the secondary white dwarf. A non-spherical CSM configuration could suggest that a small fraction of 02es-like events viewed along a favourable line of sight may be expected to display a very conspicuous early excess like SN 2022ywc.

Authors:J. van den Eijnden, L. Sidoli, M. Diaz Trigo, N. Degenaar, I. El Mellah, F. Fürst, V. Grinberg, P. Kretschmar, S. Martínez-Núñez, J. C. A. Miller-Jones, K. Postnov, T. D. Russell

Abstract: Neutron stars accreting from massive binary companions come in a wide range of types. Systems with an OB supergiant donor are often divided between persistently and transiently accreting systems, respectively called Supergiant X-ray Binaries (SgXBs) and Supergiant Fast X-ray Transients (SFXTs). The origin of this dichotomy in accretion behaviour is typically attributed to systematic differences in the massive stellar wind, the binary orbit, or magnetic field configuration, but direct observational evidence for these hypotheses remains sparse. Here, we present the results of a pilot exploration of a novel approach to this long-standing question, turning to the mm band to probe the outer regions of the stellar wind beyond the binary orbit. Specifically, we present 100-GHz NOEMA observations of a SgXB, X1908+075, and a SFXT, IGR J18410-0535. We detect the SFXT as a point source at $63.4 \pm 9.6$ $\mu$Jy, while the SgXB is not detected. The spectrum of IGR J18410-0535 is constrained to be flat or inverted by comparing with quasi-simultaneous $5.5$+$9$ GHz radio observations, ruling out non-thermal flaring and consistent with thermal wind emission. Additional X-ray measurements further constrain the wind mass loss rate and velocity of the SgXB. We compare our targets with each other and earlier wind estimates, and reflect on future opportunities using this novel observational approach to characterize stellar winds in X-ray binaries.

Authors:Miquel Miravet-Tenés, Pablo Cerdá-Durán, Martin Obergaulinger, José A. Font

Abstract: The modelling of astrophysical systems such as binary neutron star mergers or the formation of magnetars from the collapse of massive stars involves the numerical evolution of magnetised fluids at extremely large Reynolds numbers. This is a major challenge for (unresolved) direct numerical simulations which may struggle to resolve highly dynamical features as, e.g. turbulence, magnetic field amplification, or the transport of angular momentum. Sub-grid models offer a means to overcome those difficulties. In a recent paper we presented MInIT, an MHD-instability-induced-turbulence mean-field, sub-grid model based on the modelling of the turbulent (Maxwell, Reynolds, and Faraday) stress tensors. While in our previous work MInIT was assessed within the framework of the magnetorotational instability, in this paper we further evaluate the model in the context of the Kelvin-Helmholtz instability (KHI). The main difference with other sub-grid models (as e.g. the alpha-viscosity model or the gradient model) is that in MInIT we track independently the turbulent energy density at sub-grid scales, which is used, via a simple closure relation, to compute the different turbulent stresses relevant for the dynamics. The free coefficients of the model are calibrated using well resolved box simulations of magnetic turbulence generated by the KHI. We test the model against these simulations and show that it yields order-of-magnitude accurate predictions for the evolution of the turbulent Reynolds and Maxwell stresses.

Authors:L. Ducci, P. Romano, S. Vercellone, A. Santangelo

Abstract: The detection of gamma-ray emission from accreting pulsars in X-ray binaries (XRBs) has long been sought after. For some high-mass X-ray binaries (HMXBs), marginal detections have recently been reported. Regardless of whether these will be confirmed or not, future telescopes operating in the gamma-ray band could offer the sensitivity needed to achieve solid detections and possibly spectra. In view of future observational advances, we explored the expected emission above 10 GeV from XRBs, based on the Cheng & Ruderman model, where gamma-ray photons are produced by the decay of pion-0 originated by protons accelerated in the magnetosphere of an accreting pulsar fed by an accretion disc. We improved this model by considering, through Monte Carlo simulations, the development of cascades inside of and outside the accretion disc, taking into account pair and photon production processes that involve interaction with nuclei, X-ray photons from the accretion disc, and the magnetic field. We produced grids of solutions for different input parameter values of the X-ray luminosity (L_x), magnetic field strength (B), and for different properties of the region where acceleration occurs. We found that the gamma-ray luminosity spans more than five orders of magnitude, with a maximum of ~1E35 erg/s. The gamma-ray spectra show a large variety of shapes: some have most of the emission below ~100 GeV, others are harder (emission up to 10-100 TeV). We compared our results with Fermi/LAT and VERITAS detections and upper-limits of two HMXBs: A0535+26 and GROJ1008-57. More consequential comparisons will be possible when more sensitive instruments will be operational in the coming years.

Authors:Tista Mukherjee for the IceCube Collaboration

Abstract: Since the release of the Gravitational Wave Transient Catalogue GWTC-2.1 by the LIGO-Virgo collaboration, sub-threshold gravitational wave (GW) candidates are publicly available. They are expected to be released in real-time as well, in the upcoming O4 run. Using these GW candidates for multi-messenger studies complement the ongoing efforts to identify neutrino counterparts to GW events. This in turn, allows us to schedule electromagnetic follow-up searches more efficiently. However, the definition and criteria for sub-threshold candidates are pretty flexible. Finding a multi-messenger counterpart via archival studies for these candidates will help to set up strong bounds on the GW parameters which are useful for defining a GW signal as sub-threshold, thereby increasing their significance for scheduling follow-up searches. Here, we present the current status of this ongoing work with the IceCube Neutrino Observatory. We perform a selection of the sub-threshold GW candidates from GWTC-2.1 and conduct an archival search for sub-TeV neutrino counterparts detected by the dense infill array of the IceCube Neutrino Observatory, known as "DeepCore". For this, an Unbinned Maximum Likelihood (UML) method is used. We report the 90% C.L. sensitivities of this sub-TeV neutrino dataset for each selected sub-threshold GW candidate, considering the spatial and temporal correlation between the GW and neutrino events within a 1000 s time window.

Authors:J. Jormanainen, T. Hovatta, I. M. Christie, E. Lindfors, M. Petropoulou, I. Liodakis

Abstract: The origin of extremely fast variability is one of the long-standing questions in the gamma-ray astronomy of blazars. While many models explain the slower, lower energy variability, they cannot easily account for such fast flares reaching hour-to-minute time scales. Magnetic reconnection, a process where magnetic energy is converted to the acceleration of relativistic particles in the reconnection layer, is a candidate solution to this problem. In this work, we employ state-of-the-art particle-in-cell simulations in a statistical comparison with observations of a flaring episode of a well-known blazar, Mrk 421, at very high energy (VHE, E > 100 GeV). We tested the predictions of our model by generating simulated VHE light curves that we compared quantitatively with methods that we have developed for a precise evaluation of theoretical and observed data. With our analysis, we can constrain the parameter space of the model, such as the magnetic field strength of the unreconnected plasma, viewing angle and the reconnection layer orientation in the blazar jet. Our analysis favours parameter spaces with magnetic field strength 0.1 G, rather large viewing angles (6-8 degrees), and misaligned layer angles, offering a strong candidate explanation for the Doppler crisis often observed in the jets of high synchrotron peaking blazars.

Authors:Yan Li, Rong-Feng Shen, Bin-Bin Zhang

Abstract: Short-duration gamma-ray bursts (sGRBs) are commonly attributed to the mergers of double neutron stars (NSs) or the mergers of a neutron star with a black hole (BH). While the former scenario was confirmed by the event GW170817, the latter remains elusive. Here, we consider the latter scenario in which, a NS is tidally disrupted by a fast spinning low-mass BH and the accretion onto the BH launches a relativistic jet and hence produces a sGRB. The merging binary's orbit is likely misaligned with the BH's spin. Hence, the Lense-Thirring precession around the BH may cause a hyper-accreting thick disk to precess in a solid-body manner. We propose that a jet, initially aligned with the BH spin, is deflected and collimated by the wind from the disk, therefore being forced to precess along with the disk. This would result in a quasi-periodic oscillation or modulation in the gamma-ray light curve of the sGRB, with a quasi-period of $\sim 0.01-0.1$ s. The appearance of the modulation may be delayed respective to the triggering of the light curve. This feature, unique to the BH-NS merger, may have already revealed itself in a few observed sGRBs (such as GRB 130310A), and it carries the spin-obit orientation information of the merging system. Identification of this feature would be a new approach to reveal spin-orbit-misaligned merging BH-NS systems, which are likely missed by the current gravitational-wave searching strategy principally targeting aligned systems.

Authors:Boyuan Liu, Nina S. Sartorio, Robert G. Izzard, Anastasia Fialkov

Abstract: X-ray binaries (XRBs) are thought to regulate cosmic thermal and ionisation histories during the Epoch of Reionisation and Cosmic Dawn ($z\sim 5-30$). Theoretical predictions of the X-ray emission from XRBs are important for modeling such early cosmic evolution. Nevertheless, the contribution from Be-XRBs, powered by accretion of compact objects from decretion disks around rapidly rotating O/B stars, has not been investigated systematically. Be-XRBs are the largest class of high-mass XRBs (HMXBs) identified in local observations and are expected to play even more important roles in metal-poor environments at high redshifts. In light of this, we build a physically motivated model for Be-XRBs based on recent hydrodynamic simulations and observations of decretion disks. Our model is able to reproduce the observed population of Be-XRBs in the Small Magellanic Cloud with appropriate initial conditions and binary stellar evolution parameters. We derive the X-ray output from Be-XRBs as a function of metallicity in the (absolute) metallicity range $Z\in [10^{-4},0.03]$. We find that Be-XRBs can contribute a significant fraction ($\sim 60\%$) of the total X-ray budget from HMXBs observed in nearby galaxies for $Z\sim 0.0003-0.02$. A similar fraction of observed ultra-luminous ($\gtrsim 10^{39}\ \rm erg\ s^{-1}$) X-ray sources can also be explained by Be-XRBs. Moreover, the predicted metallicty dependence in our fiducial model is consistent with observations, showing a factor of $\sim 8$ increase in X-ray luminosity per unit star formation rate from $Z=0.02$ to $Z=0.0003$.

Authors:Andrzej A. Zdziarski, Srimanta Banerjee, Swadesh Chand, Gulab Dewangan, Ranjeev Misra, Michal Szanecki, Andrzej Niedzwiecki

Abstract: The spin parameter of the black hole in the accreting X-ray binary LMC X-1 has been measured in a number of studies to be $a_*\gtrsim 0.9$. These measurements were claimed to take into account both statistical and systematic (model-dependent) uncertainties. We perform new measurements using a recent simultaneous observation of LMC X-1 by NICER and NuSTAR, providing a data set of very high quality. We use the disk continuum method together with improved models for coronal Comptonization. With the standard relativistic blackbody disk model and optically thin Comptonization, we obtain values of $a_*$ similar to those obtained before. We then consider modifications to the standard disk model. Using a phenomenological color correction set to 2, we find lower values of $a_*\approx 0.64$--0.84. We then consider disks thicker than the standard one, i.e., with some dissipation in surface layers, as expected if partially supported by magnetic pressure. To account for that, we assume the disk is covered by a warm and optically thick layer, Comptonizing the emission of the underlying disk. Our model with the lowest $\chi^2$ yields then a low range of the spin, $a_*\approx 0.40^{+0.41}_{-0.32}$. That last model is also in agreement with the inverse disk temperature-luminosity relation found in this source. We conclude that determinations of the spin using the continuum method is highly sensitive to the assumptions about the disk structure.

Authors:S. I. Stathopoulos, M. Petropoulou, G. Vasilopoulos, A. Mastichiadis

Abstract: Recent associations of high-energy neutrinos with active galactic nuclei (AGN) have revived the interest in leptohadronic models of radiation from astrophysical sources. The rapid increase in the amount of acquired multi-messenger data will require soon fast numerical models that may be applied to large source samples. We develop a time-dependent leptohadronic code, LeHaMoC, that offers several notable benefits compared to other existing codes, such as versatility and speed. LeHaMoC solves the Fokker-Planck equations of photons and relativistic particles (i.e. electrons, positrons, protons, and neutrinos) produced in a homogeneous magnetized source that may also be expanding. The code utilizes a fully implicit difference scheme that allows fast computation of steady-state and dynamically evolving physical problems. We first present test cases where we compare the numerical results obtained with LeHaMoC against exact analytical solutions and numerical results computed with ATHE$\nu$A, a well-tested code of similar philosophy but different numerical implementation. We find a good agreement (within 10-30%) with the numerical results obtained with ATHE$\nu$A without evidence of systematic differences. We then demonstrate the capabilities of the code through illustrative examples. First, we fit the spectral energy distribution from a jetted AGN in the context of a synchrotron-self Compton model and a proton-synchrotron model using Bayesian inference. Second, we compute the high-energy neutrino signal and the electromagnetic cascade induced by hadronic interactions in the corona of NGC 1068. LeHaMoC is easily customized to model a variety of high-energy astrophysical sources and has the potential to become a widely utilized tool in multi-messenger astrophysics.

Authors:Helei Liu, Yong Gao, Zhaosheng Li, Akira Dohi, Weiyang Wang, Guoliang Lv, Renxin Xu

Abstract: We studied the frequency and critical mass accretion rate of millihertz quasi-periodic oscillations (mHz QPOs) using a one-zone X-ray burst model. The surface gravity is specified by two kinds of equation of states: neutron star (NS) and strange star (SS). The base flux, $Q_{b}$, is set in the range of 0-2 MeV nucleon$^{-1}$. It is found that the frequency of mHz QPO is positively correlated to the surface gravity but negatively to the base heating. The helium mass fraction has a significant influence on the oscillation frequency and luminosity. The observed 7-9 mHz QPOs can be either explained by a heavy NS/light SS with a small base flux or a heavy SS with a large base flux. As base flux increases, the critical mass accretion rate for marginally stable burning is found to be lower. Meanwhile, the impact of metallicity on the properties of mHz QPOs was investigated using one-zone model. It shows that both the frequency and critical mass accretion rate decrease as metallicity increases. An accreted NS/SS with a higher base flux and metallicity, combined with a lower surface gravity and helium mass fraction, could be responsible for the observed critical mass accretion rate ($\dot{m}\simeq 0.3\dot{m}_{\rm Edd}$). The accreted fuel would be in stable burning if base flux is over than $\sim$2 MeV nucleon$^{-1}$. This finding suggests that the accreting NSs/SSs in low-mass X-ray binaries showing no type I X-ray bursts possibly have a strong base heating.

Authors:Matti Janson for the IceCube Collaboration, Saskia Philippen for the IceCube Collaboration, Martin Rongen for the IceCube Collaboration

Abstract: The IceCube Neutrino Observatory deployed 5160 digital optical modules (DOMs) on 86 cables, called strings, in a cubic kilometer of deep glacial ice below the geographic South Pole. These record the Cherenkov light of passing charged particles. Knowledge of the DOM positions is vital for event reconstruction. While vertical positions have been calibrated, previous in-situ geometry calibration methods have been unable to measure horizontal deviations from the surface positions, largely due to degeneracies with ice model uncertainties. Thus the lateral position of the surface position of each hole is to date in almost all cases used as the lateral position of all DOMs on a given string. With the recent advances in ice modeling, two new in-situ measurements have now been undertaken. Using a large sample of muon tracks, the individual positions of all DOMs on a small number of strings around the center of the detector have been fitted. Verifying the results against LED calibration data shows that the string-average corrections improve detector modeling. Directly fitting string-average geometry corrections for the full array using LED data agrees with the average corrections as derived from muons where available. Analyses are now ongoing to obtain per-DOM positions using both methods and in addition, methods are being developed to correct the recorded arrival times for the expected scattering delay, allowing for multilateration of the positions using nanosecond-precision propagation delays.

Authors:Ming Lyu, Guobao Zhang, H. G. Wang, Federico García

Abstract: We present the spectroscopy of the neutron star low-mass X-ray binary 4U 1636-53 using six simultaneous XMM-Newton and Rossi X-ray Timing Explorer observations. We applied different self-consistent reflection models to explore the features when the disk is illuminated by either the corona or the neutron star surface. We found that the spectra could be well fitted by these two types of models, with the derived emissivity index below a typical value of 3. The relative low emissivity can be explained if the neutron star and the corona, working together as an extended illuminator, simultaneously illuminate and ionize the disk. Additionally, the derived ionization parameter in the lamppost geometry is larger than the theoretical prediction. This inconsistency likely suggests that the corona does not emit isotropically in a realistic context. Furthermore, we also found that there is a possible trend between the height of the corona and the normalization of the disk emission. This could be understood either as a variation in the reflected radiation pressure or in the context of a jet base. Finally, we found that the disk is less ionized if it is illuminated by the neutron star, indicating that the illuminating source has significant influence on the physical properties of the disk.

Authors:Ellis R. Owen, Albert K. H. Kong, Kuo-Chuan Pan

Abstract: Star-forming galaxies (SFGs) have been established as an important source population in the extra-galactic $\gamma$-ray background (EGB). Their intensive star-formation creates an abundance of environments able to accelerate particles, and these build-up a rich sea of cosmic rays (CRs). Above GeV energies, CR protons can undergo hadronic interactions with their environment to produce $\gamma$-rays. SFGs can operate as CR proton "calorimeters", where a large fraction of the CR energy is converted to $\gamma$-rays. However, CRs also deposit energy and momentum to modify the thermal and hydrodynamic conditions of the gas in SFGs, and can become a powerful driver of outflows. Such outflows are ubiquitous among some types of SFGs, and have the potential to severely degrade their CR proton calorimetry. This diminishes their contribution to the EGB. In this work, we adopt a self-consistent treatment of particle transport in outflows from SFGs to assess their calorimetry. We use 1D numerical treatments of galactic outflows driven by CRs and thermal gas pressure, accounting for the dynamical effects and interactions of CRs. We show the impact CR-driven flows have on the relative contribution of SFG populations to the EGB, and investigate the properties of SFGs that contribute most strongly.

Authors:Minjin Jeong for the IceCube Collaboration, Carsten Rott for the IceCube Collaboration

Abstract: Dark matter could decay into Standard Model particles producing neutrinos directly or indirectly. The resulting flux of neutrinos from these decays could be detectable at neutrino telescopes and would be associated with massive celestial objects where dark matter is expected to be accumulated. Recent observations of high-energy astrophysical neutrinos at IceCube might hint at a signal produced by the decay of TeV to PeV scale dark matter. This analysis searches for neutrinos from decaying dark matter in nearby galaxy clusters and galaxies. We focus on dark matter masses from 10 TeV to 1 EeV and four decay channels: $\nu\bar{\nu}$, $\tau^{+}\tau^{-}$, $W^{+}W^{-}$, $b\bar{b}$. Three galaxy clusters, seven dwarf galaxies, and the Andromeda galaxy are chosen as targets and stacked within the same source class. A well-established IceCube data sample is used, which contains 11 years of upward-going track-like events. In this contribution, we present preliminary results of the analysis.

Authors:V. L. Oknyansky, M. S. Brotherton, S. S. Tsygankov, A. V. Dodin, A. M. Tatarnikov, P. Du, D. -W. Bao, M. A. Burlak, 1 N. P. Ikonnikova, V. M. Lipunov, E. S. Gorbovskoy, V. G. Metlov, A. A. Belinski, N. I. Shatsky, S. G. Zheltouhov, N. A. Maslennikova, N. A. Huseynov, J. -M. Wang, S. Zhai, F. -N. Fang, Y. -X. Fu, H. -R. Bai, D. Kasper, J. N. McLane, J. Maithil, T. E. Zastrocky, K. A. Olson, X. Chen, D. Chelouche, R. S. Oknyansky, D. A. H. Buckley, N. V. Tyurina, A. S. Kuznetsov, R. L. Rebolo, B. -X. Zhao

Abstract: We present the results of photometric and spectroscopic monitoring campaigns of the changing look AGN NGC~2617 carried out from 2016 until 2022 and covering the wavelength range from the X-ray to the near-IR. The facilities included the telescopes of the SAI MSU, MASTER Global Robotic Net, the 2.3-m WIRO telescope, Swift, and others. We found significant variability at all wavelengths and, specifically, in the intensities and profiles of the broad Balmer lines. We measured time delays of ~ 6 days (~ 8 days) in the responses of the H-beta (H-alpha) line to continuum variations. We found the X-ray variations to correlate well with the UV and optical (with a small time delay of a few days for longer wavelengths). The K-band lagged the B band by 14 +- 4 days during the last 3 seasons, which is significantly shorter than the delays reported previously by the 2016 and 2017--2019 campaigns. Near-IR variability arises from two different emission regions: the outer part of the accretion disc and a more distant dust component. The HK-band variability is governed primarily by dust. The Balmer decrement of the broad-line components is inversely correlated with the UV flux. The change of the object's type, from Sy1 to Sy1.8, was recorded over a period of ~ 8 years. We interpret these changes as a combination of two factors: changes in the accretion rate and dust recovery along the line of sight.

Authors:Kwangmin Oh, C. Y. Hui, Jongsuk Hong, J. Takata, A. K. H. Kong, Pak-Hin Thomas Tam, Kwan-Lok Li, K. S. Cheng

Abstract: By comparing the physical properties of pulsars hosted by core-collapsed (CCed) and non-core-collapsed (Non-CCed) globular clusters (GCs), we find that pulsars in CCed GCs rotate significantly slower than their counterparts in Non-CCed GCs. Additionally, radio luminosities at 1.4 GHz in CCed GCs are higher. These findings are consistent with the scenario that dynamical interactions in GCs can interrupt angular momentum transfer processes and surface magnetic field decay during the recycling phase. Our results suggest that such effects in CCed GCs are stronger due to more frequent disruptions of compact binaries. This is further supported by the observation that both estimated disruption rates and the fraction of isolated pulsars are predominantly higher in CCed GCs.

Authors:Mitsuru Kokubo NAOJ

Abstract: We present explicit expressions for Rayleigh and Raman scattering cross-sections and phase matrices of the ground $1s$ state hydrogen atom based on the Kramers-Heisenberg dispersion formula. The Rayleigh scattering leaves the hydrogen atom in the ground-state while the Raman scattering leaves the hydrogen atom in either $ns$ ($n\geq2$; $s$-branch) or $nd$ ($n\geq3$; $d$-branch) excited state, and the Raman scattering converts incident ultraviolet (UV) photons around the Lyman resonance lines into optical-infrared (IR) photons. We show that this Raman wavelength conversion of incident flat UV continuum in dense hydrogen gas with a column density of $N_{\text{H}} > 10^{21}~\text{cm}^{-2}$ can produce broad emission features centred at Balmer, Paschen, and higher-level lines, which would mimic Doppler-broadened hydrogen lines with the velocity width of $\gtrsim 1,000~\text{km}~\text{s}^{-1}$ that could be misinterpreted as signatures of Active Galactic Nuclei, supernovae, or fast stellar winds. We show that the phase matrix of the Rayleigh and Raman $s$-branch scatterings is identical to that of the Thomson scattering while the Raman $d$-branch scattering is more isotropic, thus the Paschen and higher-level Raman features are depolarized compared to the Balmer features due to the flux contribution from the Raman $d$-branch. We argue that observations of the line widths, line flux ratios, and linear polarization of multiple optical/IR hydrogen lines are crucial to discriminate between the Raman-scattered broad emission features and Doppler-broadened emission lines.

Authors:Sumeet Kulkarni, Nathan K. Johnson-McDaniel, Khun Sang Phukon, N. V. Krishnendu, Anuradha Gupta

Abstract: The spin orientations of spinning binary black hole (BBH) mergers detected by ground-based gravitational wave detectors such as LIGO and Virgo can provide important clues about the formation of such binaries. However, these spin tilts, i.e., the angles between the spin vector of each black hole and the binary's orbital angular momentum vector, can change due to precessional effects as the black holes evolve from a large separation to their merger. The tilts inferred at a frequency in the sensitive band of the detectors by comparing the signal with theoretical waveforms can thus be significantly different from the tilts when the binary originally formed. These tilts at the binary's formation are well approximated in many scenarios by evolving the BBH backwards in time to a formally infinite separation. Using the tilts at infinite separation also places all binaries on an equal footing in analyzing their population properties. In this paper, we perform parameter estimation for simulated BBHs and investigate the differences between the tilts one infers directly close to merger and those obtained by evolving back to infinite separation. We select simulated observations such that their configurations show particularly large differences in their orientations close to merger and at infinity. While these differences may be buried in the statistical noise for current detections, we show that in future plus-era (A$+$ and Virgo$+$) detectors, they can be easily distinguished in some cases. We also consider the tilts at infinity for BBHs in various spin morphologies and at the endpoint of the up-down instability. In particular, we find that we are able to easily identify the up-down instability cases as such from the tilts at infinity.

Authors:Amanda M. Farah, Maya Fishbach, Daniel E. Holz

Abstract: When modeling the population of merging binary black holes, analyses generally focus on characterizing the distribution of primary (i.e. more massive) black holes in the binary, while simplistic prescriptions are used for the distribution of secondary masses. However, the secondary mass distribution provides a fundamental observational constraint on the formation history of coalescing binary black holes. If both black holes experience similar stellar evolutionary processes prior to collapse, as might be expected in dynamical formation channels, the primary and secondary mass distributions would show similar features. If they follow distinct evolutionary pathways (for example, due to binary interactions that break symmetry between the initially more massive and less massive star), their mass distributions may differ. We explicitly fit the secondary mass distribution, finding that if the primary and secondary mass distributions are different, the previously-identified peak in the primary mass distribution may be driven by an even larger peak in the secondary mass distribution. Alternatively, if we assume that the two masses are drawn from the same underlying distribution, they both show a peak at $31.4_{-2.6}^{+2.3} \, M_{\odot}$. This value is shifted lower than that obtained when assuming the peak only exists in the marginal primary mass distribution, placing this feature in further tension with expectations from a pulsational pair-instability supernova pileup. We anticipate that by the end of the fifth LIGO-Virgo-KAGRA observing run, we will be able to determine whether the data prefer distinct or identical component mass distributions to $>4\sigma$, providing important clues to the formation history of coalescing binary black holes.

Authors:Rahul Jayaraman MIT, Michael Fausnaugh MIT, George R. Ricker MIT, Roland Vanderspek MIT

Abstract: Throughout the past three decades, only a few tens of observations have been made of optical flashes contemporaneous with gamma-ray bursts (GRBs), despite the thousands of GRBs that have been detected during that same timeframe. In this work, we present light curves from the Transiting Exoplanet Survey Satellite (TESS) for a sample of 7 GRBs that were localized to within 10" by the Swift X-ray Telescope. For each burst, we characterize both the prompt emission, if it exists, and the afterglow, and conduct searches for late-time emission from a supernova or kilonova component. We also constrain the physical parameters of the burst based on the TESS light curve, and present a novel method to account for the effects of TESS's cosmic ray mitigation strategy on the observed flux from these GRBs. This allows us to establish upper limits on the true magnitude of any GRB-associated optical flash. Finally, we discuss how TESS's continuous monitoring and new weekly downlink schedule are proving invaluable in the rapid follow-up and characterization of short-duration transients, including GRBs; these could potentially enable TESS to detect electromagnetic counterparts to gravitational-wave events.

Authors:Ben Pottie, Luigi Gallo, Adam Gonzalez, Jon Miller

Abstract: Eclipsing of the X-ray emitting region in active galactic nuclei (AGN) is a potentially powerful probe to examine the AGN environment and absorber properties. Here we study the eclipse data from the 2016 XMM-Newton observation of NGC 6814 using a colour-colour analysis. Colours (i.e. hardness ratios) can provide the advantage of better time-resolution over spectral analysis alone. Colour-colour grids are constructed to examine the effects of different parameters on the observed spectral variability during the eclipse. Consistent with previous spectral analysis, the variations are dominated by changes in the column density and covering fraction of the absorber. However, during maximum eclipse the behaviour of the absorber changes. Just after ingress, the eclipse is described by changes in column density and covering fraction, but prior to egress, the variations are dominated by changes in column density alone. Simulations are carried out to consider possible absorber geometries that might produce this behaviour. The behaviour is inconsistent with a single, homogeneous cloud, but simulations suggest that multiple clouds, perhaps embedded in a highly ionised halo, could reproduce the results. In addition, we determine the orbital covering factor (fraction of orbital path-length) based on evidence of several eclipses in the 2016, 64-day Swift light curve. We estimate that ~ 2-4 per cent of the orbit is covered by obscuring clouds and that the distribution of clouds is not isotropic.

Authors:Odelia Teboul, Brian D. Metzger

Abstract: Only a tiny fraction ~ 1% of stellar tidal disruption events (TDE) generate powerful relativistic jets evidenced by luminous hard X-ray and radio emissions. We propose that a key property responsible for both this surprisingly low rate and a variety of other observations is the typically large misalignment {\psi} between the orbital plane of the star and the spin axis of the supermassive black hole (SMBH). Such misaligned disk/jet systems undergo Lense-Thirring precession together about the SMBH spin axis. We find that TDE disks precess sufficiently rapidly that winds from the accretion disk will encase the system on large scales in a quasi-spherical outflow. We derive the critical jet efficiency {\eta} > {\eta}crit for both aligned and misaligned precessing jets to successfully escape from the disk-wind ejecta. As {\eta}crit is higher for precessing jets, less powerful jets only escape after alignment with the SMBH spin. Alignment can occur through magneto-spin or hydrodynamic mechanisms, which we estimate occur on typical timescales of weeks and years, respectively. The dominant mechanism depends on {\eta} and the orbital penetration factor \b{eta}. Hence depending only on intrinsic parameters of the event {{\psi},{\eta},\b{eta}}, we propose that each TDE jet can either escape prior to alignment, thus exhibiting erratic X-ray light curve and two-component radio afterglow (e.g., Swift J1644+57) or escape after alignment. Relatively rapid magneto-spin alignments produce relativistic jets exhibiting X-ray power-law decay and bright afterglows (e.g., AT2022cmc), while long hydrodynamic alignments give rise to late jet escape and delayed radio flares (e.g., AT2018hyz).

Authors:P. Kosec, D. Pasham, E. Kara, F. Tombesi

Abstract: Tidal disruption events (TDEs) are exotic transients that can lead to temporary super-Eddington accretion onto a supermassive black hole. Such accretion mode is naturally expected to result in powerful outflows of ionized matter. However, to date such an outflow has only been directly detected in the X-ray band in a single TDE, ASASSN-14li. This outflow has a low velocity of just a few 100 km/s, although there is also evidence for a second, ultra-fast phase. Here we present the detection of a low-velocity outflow in a second TDE, ASASSN-20qc. The high-resolution X-ray spectrum reveals an array of narrow absorption lines, each blueshifted by a few 100 km/s, which cannot be described by a single photo-ionization phase. For the first time, we confirm the multiphase nature of a TDE outflow, with at least two phases and two distinct velocity components. One highly ionized phase is outflowing at $910^{+90}_{-80}$ km/s, while a lower ionization component is blueshifted by $400_{-120}^{+100}$ km/s. We perform time-resolved analysis of the X-ray spectrum and detect that, surprisingly, the mildly ionized absorber strongly varies in ionization parameter over the course of a single 60 ks observation, indicating that its distance from the black hole may be as low as 400 gravitational radii. We discuss these findings in the context of TDEs and compare this newly detected outflow with that of ASASSN-14li.

Authors:Tobias Fischer, Gang Guo, Karlheinz Langanke, Gabriel Martinez-Pinedo, Yong-Zhong Qian, Meng-Ru Wu

Abstract: Neutrinos are known to play important roles in many astrophysical scenarios from the early period of the big bang to current stellar evolution being a unique messenger of the fusion reactions occurring in the center of our sun. In particular, neutrinos are crucial in determining the dynamics and the composition evolution in explosive events such as core-collapse supernovae and the merger of two neutron stars. In this paper, we review the current understanding of supernovae and binary neutron star mergers by focusing on the role of neutrinos therein. Several recent improvements on the theoretical modeling of neutrino interaction rates in nuclear matter as well as their impact on the heavy element nucleosynthesis in the supernova neutrino-driven wind are discussed, including the neutrino-nucleon opacity at the mean field level taking into account the relativistic kinematics of nucleons, the effect due to the nucleon-nucleon correlation, and the nucleon-nucleon bremsstrahlung. We also review the framework used to compute the neutrino-nucleus interactions and the up-to-date yield prediction for isotopes from neutrino nucleosynthesis occurring in the outer envelope of the supernova progenitor star during the explosion. Here improved predictions of energy spectra of supernova neutrinos of all flavors have had significant impact on the nucleosynthesis yields. Rapid progresses in modeling the flavor oscillations of neutrinos in these environments, including several novel mechanisms for collective neutrino oscillations and their potential impacts on various nucleosynthesis processes are summarized.

Authors:Nissim Fraija, Maria G. Dainotti, B. Betancourt Kamenetskaia, D. Levine, A. Galvan-Gamez

Abstract: The Second Gamma-ray Burst Catalog (2FLGC) was announced by the Fermi Large Area Telescope (Fermi-LAT) Collaboration. It includes 29 bursts with photon energy higher than 10 GeV. Gamma-ray burst (GRB) afterglow observations have been adequately explained by the classic synchrotron forward-shock model, however, photon energies greater than 10 GeV from these transient events are challenging, if not impossible, to characterize using this afterglow model. Recently, the closure relations (CRs) of the synchrotron self-Compton (SSC) forward-shock model evolving in a stellar wind and homogeneous medium was presented to analyze the evolution of the spectral and temporal indexes of those bursts reported in 2FLGC. In this work, we provide the CRs of the same afterglow model, but evolving in an intermediate density profile ($\propto {\rm r^{-k}}$) with ${\rm 0\leq k \leq2.5}$, taking into account the adiabatic/radiative regime and with/without energy injection for any value of the electron spectral index. The results show that the current model accounts for a considerable subset of GRBs that cannot be interpreted in either stellar-wind or homogeneous afterglow SSC model. The analysis indicates that the best-stratified scenario is most consistent with ${\rm k=0.5}$ for no-energy injection and ${\rm k=2.5}$ for energy injection.

Authors:David Guevel for the IceCube Collaboration, Ke Fang for the IceCube Collaboration

Abstract: The origin of most astrophysical neutrinos is unknown, but extragalactic neutrino sources may follow the spatial distribution of the large-scale structure of the universe. Galaxies also follow the same large scale distribution, so establishing a correlation between galaxies and IceCube neutrinos could help identify the origins of the diffuse neutrinos observed by IceCube. Following a preliminary study based on the WISE and 2MASS catalogs, we will investigate an updated galaxy catalog with improved redshift measurements and reduced stellar contamination. Our IceCube data sample consists of track-like muon neutrinos selected from the Northern sky. The excellent angular resolution of track-like events and low contamination with atmospheric muons is necessary for the sensitivity of the analysis. Unlike a point source stacking analysis, the calculation of the cross correlation does not scale with the number of entries in the catalog, making the work tractable for catalogs with millions of objects. We present the development and performance of a two-point cross correlation of IceCube neutrinos with a tracer of the large scale structure.

Authors:Carlo Ferrigno, Antonino D'Aì, Elena Ambrosi

Abstract: We introduce a method for extracting spectral information from energy-resolved light curves folded at the neutron star spin period (known as pulse profiles) in accreting X-ray binaries. Spectra of these sources are sometimes characterized by features superimposed on a smooth continuum, such as iron emission lines and cyclotron resonant scattering features. We address here the question on how to derive quantitative constraints on such features from energy-dependent changes in the pulse profiles. We developed a robust method for determining in each energy-selected bin the value of the pulsed fraction using the fast Fourier transform opportunely truncated at the number of harmonics needed to satisfactorily describe the actual profile. We determined the uncertainty on this value by sampling through Monte Carlo simulations a total of 1000 faked profiles. We rebinned the energy-resolved pulse profiles to have a constant minimum signal-to-noise ratio throughout the whole energy band. Finally we characterize the dependence of the energy-resolved pulsed fraction using a phenomenological polynomial model and search for features corresponding to spectral signatures of iron emission or cyclotron lines using Gaussian line profiles. We apply our method to a representative sample of NuSTAR observations of well-known accreting X-ray pulsars. We show that, with this method, it is possible to characterize the pulsed fraction spectra, and to constrain the position and widths of such features with a precision comparable with the spectral results. We also explore how harmonic decomposition, correlation, and lag spectra might be used as additional probes for detection and characterization of such features.

Authors:Carlos Pastor-Marcos, Pablo Cerdá-Durán, Daniel Walker, Alejandro Torres-Forné, Ernazar Abdikamalov, Sherwood Richers, José Antonio Font

Abstract: Core-collapse supernovae (CCSNe) are prime candidates for gravitational-wave detectors. The analysis of their complex waveforms can potentially provide information on the physical processes operating during the collapse of the iron cores of massive stars. In this work we analyze the early-bounce rapidly rotating CCSN signals reported in the waveform catalog of Richers et al 2017, which comprises over 1800 axisymmetric simulations extending up to about $10$~ms of post-bounce evolution. It was previously established that for a large range of progenitors, the amplitude of the bounce signal, $\Delta h$, is proportional to the ratio of rotational-kinetic energy to potential energy, T/|W|, and the peak frequency, $f_{\rm peak}$, is proportional to the square root of the central rest-mass density. In this work, we exploit these relations to suggest that it could be possible to use such waveforms to infer protoneutron star properties from a future gravitational wave observation, if the distance and inclination are well known. Our approach relies on the ability to describe a subset of the waveforms in the early post-bounce phase in a simple template form depending only on two parameters, $\Delta h$ and $f_{\rm peak}$. We use this template to perform a Bayesian inference analysis of waveform injections in Gaussian colored noise for a network of three gravitational wave detectors formed by Advanced LIGO and Advanced Virgo. We show that it is possible to recover the injected parameters, peak frequency and amplitude, with an accuracy better than 10% for more than 50% of the detectable signals (given known distance and inclination angle). However, inference on waveforms from outside the Richers catalog is not reliable, indicating a need for carefully verified waveforms of the first 10 ms after bounce of rapidly rotating supernovae of different progenitors with agreement between different codes.

Authors:Khaled Alizai, Jérôme Chenevez, Andrew Cumming, Nathalie Degenaar, Maurizio Falanga, Duncan K. Galloway, Jean J. M. in `t Zand, Gaurava K. Jaisawal, Laurens Keek, Erik Kuulkers, Nathanael Lampe, Hendrik Schatz, Motoko Serino

Abstract: Rare, energetic (long) thermonuclear (Type I) X-ray bursts are classified either as intermediate-duration or superbursts, based on their duration. Intermediate-duration bursts lasting a few to tens of minutes are thought to arise from the thermonuclear runaway of a relatively thick (10^10 g/cm2) helium layer, while superbursts lasting hours are attributed to the detonation of an underlying carbon layer. We present a catalogue of 84 long thermonuclear bursts from 40 low-mass X-ray binaries, and defined from a new set of criteria distinguishing them from the more frequent short bursts. The three criteria are: (1) a total energy release larger than 10^40 erg, (2) a photospheric radius expansion phase longer than 10 s, and (3) a burst time-scale longer than 70 s. This work is based on a comprehensive systematic analysis of 70 bursts found with INTEGRAL, RXTE, Swift, BeppoSAX, MAXI, and NICER, as well as 14 long bursts from the literature that were detected with earlier generations of X-ray instruments. For each burst, we measure its peak flux and fluence, which eventually allows us to confirm the distinction between intermediate-duration bursts and superbursts. Additionally, we list 18 bursts that only partially meet the above inclusion criteria, possibly bridging the gap between normal and intermediate-duration bursts. With this catalogue, we significantly increase the number of long-duration bursts included in the MINBAR and thereby provide a substantial sample of these rare X-ray bursts for further study.

Authors:Ritesh Ghosh, Sibasish Laha, Eileen Meyer, Agniva Roychowdhury, Xiaolong Yang, J. A. Acosta Pulido, Suvendu Rakshit, Shivangi Pandey, Josefa Becerra Gonzalez, Ehud Behar, Luigi C. Gallo, Francesca Panessa, Stefano Bianchi, Fabio La Franca, Nicolas Scepi, Mitchell C. Begelman, Anna Lia Longinotti, Elisabeta Lusso, Samantha Oates, Matt Nicholl, S. Bradley Cenko, Brendan O Connor, Erica Hammerstein, Jincen Jose, Krisztina Eva Gabanyi, Federica Ricci, Sabyasachi Chattopadhyay

Abstract: 1ES1927+654 is a nearby active galactic nucleus that has shown an enigmatic outburst in optical/UV followed by X-rays, exhibiting strange variability patterns at timescales of months-years. Here we report the unusual X-ray, UV, and radio variability of the source in its post-flare state (Jan 2022- May 2023). Firstly, we detect an increase in the soft X-ray (0.3-2 keV) flux from May 2022- May 2023 by almost a factor of five, which we call the bright-soft-state. The hard X-ray 2-10 keV flux increased by a factor of two, while the UV flux density did not show any significant changes ($\le 30\%$) in the same period. The integrated energy pumped into the soft and hard X-ray during this period of eleven months is $\sim 3.57\times 10^{50}$ erg and $5.9\times 10^{49}$ erg, respectively. From the energetics, it is evident that whatever is producing the soft excess (SE) is pumping out more energy than either the UV or hard X-ray source. Since the energy source presumably is ultimately the accretion of matter onto the SMBH, the SE emitting region must be receiving the majority of this energy. In addition, the source does not follow the typical disc-corona relation found in AGNs, neither in the initial flare (in 2017-2019) nor in the current bright soft state (2022-2023). We found that the core (<1 pc) radio emission at 5 GHz gradually increased till March 2022 but showed a dip in August 2022. The G\"udel Benz relation ($L_{\rm radio}/L_{\rm X-ray}\sim 10^{-5}$), however, is still within the expected range for radio-quiet AGN and further follow-up radio observations are currently being undertaken.

Authors:The LIGO Scientific Collaboration, the Virgo Collaboration, the KAGRA Collaboration, A. G. Abac, R. Abbott, H. Abe, F. Acernese, K. Ackley, C. Adamcewicz, S. Adhicary, N. Adhikari, R. X. Adhikari, V. K. Adkins, V. B. Adya, C. Affeldt, D. Agarwal, M. Agathos, O. D. Aguiar, I. Aguilar, L. Aiello, A. Ain, P. Ajith, T. Akutsu, S. Albanesi, R. A. Alfaidi, A. Al-Jodah, C. Alléné, A. Allocca, M. Almualla, P. A. Altin, S. Álvarez-López, A. Amato, L. Amez-Droz, A. Amorosi, S. Anand, A. Ananyeva, R. Andersen, S. B. Anderson, W. G. Anderson, M. Andia, M. Ando, T. Andrade, N. Andres, M. Andrés-Carcasona, T. Andrić, S. Ansoldi, J. M. Antelis, S. Antier, M. Aoumi, T. Apostolatos, E. Z. Appavuravther, S. Appert, S. K. Apple, K. Arai, A. Araya, M. C. Araya, J. S. Areeda, N. Aritomi, F. Armato, N. Arnaud, M. Arogeti, S. M. Aronson, K. G. Arun, G. Ashton, Y. Aso, M. Assiduo, S. Assis de Souza Melo, S. M. Aston, P. Astone, F. Aubin, K. AultONeal, S. Babak, A. Badalyan, F. Badaracco, C. Badger, S. Bae, S. Bagnasco, Y. Bai, J. G. Baier, R. Bajpai, T. Baka, M. Ball, G. Ballardin, S. W. Ballmer, G. Baltus, S. Banagiri, B. Banerjee, D. Bankar, P. Baral, J. C. Barayoga, J. Barber, B. C. Barish, D. Barker, P. Barneo, F. Barone, B. Barr, L. Barsotti, M. Barsuglia, D. Barta, S. D. Barthelmy, M. A. Barton, I. Bartos, S. Basak, A. Basalaev, R. Bassiri, A. Basti, M. Bawaj, P. Baxi, J. C. Bayley, A. C. Baylor, M. Bazzan, B. Bécsy, V. M. Bedakihale, F. Beirnaert, M. Bejger, A. S. Bell, V. Benedetto, D. Beniwal, W. Benoit, J. D. Bentley, M. Ben Yaala, S. Bera, M. Berbel, F. Bergamin, B. K. Berger, S. Bernuzzi, M. Beroiz, C. P. L. Berry, D. Bersanetti, A. Bertolini, J. Betzwieser, D. Beveridge, N. Bevins, R. Bhandare, A. V. Bhandari, U. Bhardwaj, R. Bhatt, D. Bhattacharjee, S. Bhaumik, A. Bianchi, I. A. Bilenko, M. Bilicki, G. Billingsley, A. Binetti, S. Bini, O. Birnholtz, S. Biscans, M. Bischi, S. Biscoveanu, A. Bisht, M. Bitossi, M. -A. Bizouard, J. K. Blackburn, C. D. Blair, D. G. Blair, F. Bobba, N. Bode, M. Boër, G. Bogaert, G. Boileau, M. Boldrini, G. N. Bolingbroke, L. D. Bonavena, R. Bondarescu, F. Bondu, E. Bonilla, M. S. Bonilla, R. Bonnand, P. Booker, V. Boschi, S. Bose, V. Bossilkov, V. Boudart, A. Bozzi, C. Bradaschia, P. R. Brady, M. Braglia, A. Branch, M. Branchesi, M. Breschi, T. Briant, A. Brillet, M. Brinkmann, P. Brockill, A. F. Brooks, D. D. Brown, M. L. Brozzetti, S. Brunett, G. Bruno, R. Bruntz, J. Bryant, F. Bucci, J. Buchanan, O. Bulashenko, T. Bulik, H. J. Bulten, A. Buonanno, K. Burtnyk, R. Buscicchio, D. Buskulic, C. Buy, G. S. Cabourn Davies, G. Cabras, R. Cabrita, L. Cadonati, G. Cagnoli, C. Cahillane, H. W. Cain III, J. Calderón Bustillo, J. D. Callaghan, T. A. Callister, E. Calloni, J. B. Camp, M. Canepa, G. Caneva Santoro, M. Cannavacciuolo, K. C. Cannon, H. Cao, Z. Cao, L. A. Capistran, E. Capocasa, E. Capote, G. Carapella, F. Carbognani, M. Carlassara, J. B. Carlin, M. Carpinelli, J. J. Carter, G. Carullo, J. Casanueva Diaz, C. Casentini, G. Castaldi, S. Y. Castro-Lucas, S. Caudill, M. Cavaglià, R. Cavalieri, G. Cella, P. Cerdá-Durán, E. Cesarini, W. Chaibi, S. Chalathadka-Subrahmanya, C. Chan, J. C. L. Chan, K. H. M. Chan, M. Chan, W. L. Chan, K. Chandra, I. P. Chang, R. -J. Chang, W. Chang, P. Chanial, S. Chao, C. Chapman-Bird, E. L. Charlton, P. Charlton, E. Chassande-Mottin, L. Chastain, C. Chatterjee, Debarati Chatterjee, Deep Chatterjee, M. Chaturvedi, S. Chaty, K. Chatziioannou, A. Chen, A. H. -Y. Chen, D. Chen, H. Chen, H. Y. Chen, J. Chen, K. H. Chen, X. Chen, Y. -R. Chen, Y. Chen, H. Cheng, P. Chessa, H. Y. Chia, F. Chiadini, C. Chiang, G. Chiarini, A. Chiba, R. Chiba, R. Chierici, A. Chincarini, M. L. Chiofalo, A. Chiummo, C. Chou, S. Choudhary, N. Christensen, S. S. Y. Chua, K. W. Chung, G. Ciani, P. Ciecielag, M. Cieślar, M. Cifaldi, A. A. Ciobanu, R. Ciolfi, F. Clara, J. A. Clark, T. A. Clarke, P. Clearwater, S. Clesse, F. Cleva, E. Coccia, E. Codazzo, P. -F. Cohadon, M. Colleoni, C. G. Collette, J. Collins, A. Colombo, M. Colpi, C. M. Compton, L. Conti, S. J. Cooper, T. R. Corbitt, I. Cordero-Carrión, S. Corezzi, N. J. Cornish, A. Corsi, S. Cortese, C. A. Costa, R. Cottingham, M. W. Coughlin, A. Couineaux, J. -P. Coulon, S. T. Countryman, J. -F. Coupechoux, B. Cousins, P. Couvares, D. M. Coward, M. J. Cowart, B. D. Cowburn, D. C. Coyne, R. Coyne, K. Craig, J. D. E. Creighton, T. D. Creighton, A. W. Criswell, J. C. G. Crockett-Gray, M. Croquette, R. Crouch, S. G. Crowder, J. R. Cudell, T. J. Cullen, A. Cumming, E. Cuoco, M. Curyło, M. Cusinato, P. Dabadie, T. Dal Canton, S. Dall'Osso, G. Dálya, B. D'Angelo, S. Danilishin, S. D'Antonio, K. Danzmann, K. E. Darroch, C. Darsow-Fromm, L. P. Dartez, A. Dasgupta, S. Datta, V. Dattilo, A. Daumas, I. Dave, A. Davenport, M. Davier, D. Davis, M. C. Davis, E. J. Daw, M. Dax, M. Deenadayalan, J. Degallaix, M. De Laurentis, S. Deléglise, V. Del Favero, F. De Lillo, D. Dell'Aquila, W. Del Pozzo, F. De Marco, F. De Matteis, V. D'Emilio, N. Demos, T. Dent, A. Depasse, R. De Pietri, R. De Rosa, C. De Rossi, R. De Simone, S. Dhurandhar, R. Diab, P. Z. Diamond, M. C. Díaz, N. A. Didio, T. Dietrich, L. Di Fiore, C. Di Fronzo, F. Di Giovanni, M. Di Giovanni, T. Di Girolamo, D. Diksha, A. Di Lieto, A. Di Michele, J. Ding, S. Di Pace, I. Di Palma, F. Di Renzo, Divyajyoti, A. Dmitriev, Z. Doctor, E. Dohmen, P. P. Doleva, L. Donahue, L. D'Onofrio, F. Donovan, K. L. Dooley, T. Dooney, S. Doravari, O. Dorosh, M. Drago, J. C. Driggers, Y. Drori, H. Du, J. -G. Ducoin, L. Dunn, U. Dupletsa, D. D'Urso, H. Duval, P. -A. Duverne, S. E. Dwyer, C. Eassa, M. Ebersold, T. Eckhardt, G. Eddolls, B. Edelman, T. B. Edo, O. Edy, A. Effler, J. Eichholz, H. Einsle, M. Eisenmann, R. A. Eisenstein, A. Ejlli, E. Engelby, A. J. Engl, L. Errico, R. C. Essick, H. Estellés, D. Estevez, T. Etzel, C. R. Evans, M. Evans, T. M. Evans, T. Evstafyeva, B. E. Ewing, J. M. Ezquiaga, F. Fabrizi, F. Faedi, V. Fafone, H. Fair, S. Fairhurst, P. C. Fan, A. M. Farah, B. Farr, W. M. Farr, E. J. Fauchon-Jones, G. Favaro, M. Favata, M. Fays, J. Feicht, M. M. Fejer, E. Fenyvesi, D. L. Ferguson, I. Ferrante, T. A. Ferreira, F. Fidecaro, A. Fiori, I. Fiori, M. Fishbach, R. P. Fisher, R. Fittipaldi, V. Fiumara, R. Flaminio, S. M. Fleischer, L. S. Fleming, E. Floden, H. Fong, J. A. Font, B. Fornal, P. W. F. Forsyth, K. Franceschetti, A. Franke, S. Frasca, F. Frasconi, A. Frattale Mascioli, Z. Frei, A. Freise, O. Freitas, R. Frey, W. Frischhertz, P. Fritschel, V. V. Frolov, G. G. Fronzé, S. Fujii, I. Fukunaga, P. Fulda, M. Fyffe, W. E. Gabella, B. Gadre, J. R. Gair, J. Gais, S. Galaudage, S. Gallardo, R. Gamba, D. Ganapathy, A. Ganguly, S. G. Gaonkar, B. Garaventa, J. Garcia-Bellido, C. García-Núñez, C. García-Quirós, J. W. Gardner, K. A. Gardner, J. Gargiulo, F. Garufi, C. Gasbarra, B. Gateley, V. Gayathri, G. Gemme, A. Gennai, J. George, O. Gerberding, L. Gergely, N. Ghadiri, Abhirup Ghosh, Archisman Ghosh, Shaon Ghosh, Shrobana Ghosh, Suprovo Ghosh, Tathagata Ghosh, L. Giacoppo, J. A. Giaime, K. D. Giardina, D. R. Gibson, C. Gier, P. Giri, F. Gissi, S. Gkaitatzis, J. Glanzer, A. E. Gleckl, F. Glotin, J. Godfrey, P. Godwin, E. Goetz, R. Goetz, J. Golomb, S. Gomez Lopez, B. Goncharov, G. González, A. W. Goodwin-Jones, M. Gosselin, R. Gouaty, D. W. Gould, S. Goyal, B. Grace, A. Grado, V. Graham, A. E. Granados, M. Granata, V. Granata, S. Gras, P. Grassia, C. Gray, R. Gray, G. Greco, A. C. Green, S. M. Green, S. R. Green, A. M. Gretarsson, E. M. Gretarsson, D. Griffith, W. L. Griffiths, H. L. Griggs, G. Grignani, A. Grimaldi, C. Grimaud, H. Grote, A. S. Gruson, D. Guerra, D. Guetta, G. M. Guidi, A. R. Guimaraes, H. K. Gulati, F. Gulminelli, A. M. Gunny, H. Guo, Y. Guo, Anchal Gupta, Anuradha Gupta, Ish Gupta, N. C. Gupta, P. Gupta, S. K. Gupta, N. Gupte, R. Gurav, J. Gurs, E. K. Gustafson, N. Gutierrez, F. Guzman, D. Haba, L. Haegel, G. Hain, S. Haino, O. Halim, E. D. Hall, E. Z. Hamilton, G. Hammond, W. -B. Han, M. Haney, J. Hanks, C. Hanna, M. D. Hannam, O. A. Hannuksela, A. G. Hanselman, H. Hansen, J. Hanson, R. Harada, T. Harder, K. Haris, T. Harmark, J. Harms, G. M. Harry, I. W. Harry, D. Hartwig, B. Haskell, C. -J. Haster, J. S. Hathaway, K. Haughian, H. Hayakawa, K. Hayama, F. J. Hayes, J. Healy, A. Heffernan, A. Heidmann, M. C. Heintze, J. Heinze, J. Heinzel, H. Heitmann, F. Hellman, P. Hello, A. F. Helmling-Cornell, G. Hemming, M. Hendry, I. S. Heng, E. Hennes, J. -S. Hennig, M. Hennig, C. Henshaw, A. Hernandez, T. Hertog, M. Heurs, A. L. Hewitt, S. Higginbotham, S. Hild, P. Hill, Y. Himemoto, A. S. Hines, N. Hirata, C. Hirose, J. Ho, S. Hoang, S. Hochheim, D. Hofman, J. N. Hohmann, N. A. Holland, K. Holley-Bockelmann, I. J. Hollows, Z. J. Holmes, D. E. Holz, C. Hong, Q. Hong, J. Hornung, S. Hoshino, J. Hough, S. Hourihane, E. J. Howell, C. G. Hoy, D. Hoyland, H. -F. Hsieh, C. Hsiung, H. C. Hsu, S. -C. Hsu, W. -F. Hsu, P. Hu, Q. Hu, H. Y. Huang, Y. -J. Huang, Y. Huang, Y. T. Huang, M. T. Hübner, A. D. Huddart, B. Hughey, D. C. Y. Hui, V. Hui, R. Hur, S. Husa, R. Huxford, T. Huynh-Dinh, J. Hyland, A. Iakovlev, G. A. Iandolo, A. Iess, K. Inayoshi, Y. Inoue, G. Iorio, P. Iosif, J. Irwin, M. Isi, M. A. Ismail, Y. Itoh, M. Iwaya, B. R. Iyer, V. JaberianHamedan, T. Jacqmin, P. -E. Jacquet, S. J. Jadhav, S. P. Jadhav, D. Jain, T. Jain, A. L. James, P. A. James, R. Jamshidi, A. Z. Jan, K. Jani, L. Janiurek, J. Janquart, K. Janssens, N. N. Janthalur, S. Jaraba, P. Jaranowski, S. Jarov, P. Jasal, R. Jaume, W. Javed, K. Jenner, A. Jennings, W. Jia, J. Jiang, H. -B. Jin, K. Johansmeyer, G. R. Johns, N. A. Johnson, R. Johnston, N. Johny, D. H. Jones, D. I. Jones, R. Jones, P. Joshi, L. Ju, K. Jung, J. Junker, V. Juste, T. Kajita, C. Kalaghatgi, V. Kalogera, M. Kamiizumi, N. Kanda, S. Kandhasamy, G. Kang, J. B. Kanner, S. J. Kapadia, D. P. Kapasi, S. Karat, C. Karathanasis, S. Karki, T. Karydas, Y. A. 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Abstract: Despite the growing number of confident binary black hole coalescences observed through gravitational waves so far, the astrophysical origin of these binaries remains uncertain. Orbital eccentricity is one of the clearest tracers of binary formation channels. Identifying binary eccentricity, however, remains challenging due to the limited availability of gravitational waveforms that include effects of eccentricity. Here, we present observational results for a waveform-independent search sensitive to eccentric black hole coalescences, covering the third observing run (O3) of the LIGO and Virgo detectors. We identified no new high-significance candidates beyond those that were already identified with searches focusing on quasi-circular binaries. We determine the sensitivity of our search to high-mass (total mass $M>70$ $M_\odot$) binaries covering eccentricities up to 0.3 at 15 Hz orbital frequency, and use this to compare model predictions to search results. Assuming all detections are indeed quasi-circular, for our fiducial population model, we place an upper limit for the merger rate density of high-mass binaries with eccentricities $0 < e \leq 0.3$ at $0.33$ Gpc$^{-3}$ yr$^{-1}$ at 90\% confidence level.

Authors:Mao Ogawa, Keiichi Maeda, Miho Kawabata

Abstract: It has been widely accepted that Type Ia supernovae (SNe Ia) are thermonuclear explosions of a CO white dwarf. However, the natures of the progenitor system(s) and explosion mechanism(s) are still unclarified. Thanks to the recent development of transient observations, they are now frequently discovered shortly after the explosion, followed by rapid spectroscopic observations. In this study, by modeling very early-phase spectra of SNe Ia, we try to constrain the explosion models of SNe Ia. By using the Monte Carlo radiation transfer code, TARDIS, we estimate the properties of their outermost ejecta. We find that the photospheric velocity of normal-velocity supernovae (NV SNe) in the first week is $\sim$15000 km s$^{-1}$. The outer velocity, to which the carbon burning extends, spans the range between $\sim$20000 and 25000 km s$^{-1}$. The ejecta density of NV SNe also shows a large diversity. For high-velocity supernovae (HV SNe) and 1999aa-like SNe, the photospheric velocity is higher, $\sim$20000 km s$^{-1}$. They are different in the photospheric density, with HV SNe having higher density than 1999aa-like SNe. For all these types, we show that the outermost composition is closely related to the outermost ejecta density; the carbon burning layer and the unburnt carbon layer are found in the higher-density and lower-density objects, respectively. This finding suggests that there might be two sequences, the high-density and carbon-poor group (HV SNe and some NV SNe) and the low-density and carbon-rich group (1999aa-like and other NV SNe), which may be associated with different progenitor channels.

Authors:Ersilia Guarini, Irene Tamborra, Raffaella Margutti, Enrico Ramirez-Ruiz

Abstract: Collapsing massive stars lead to a broad range of astrophysical transients, whose multi-wavelength emission is powered by a variety of processes including radioactive decay, activity of the central engine, and interaction of the outflows with a dense circumstellar medium. These transients are also candidate factories of neutrinos with energy up to hundreds of PeV. We review the energy released by such astrophysical objects across the electromagnetic wavebands as well as neutrinos, in order to outline a strategy to optimize multi-messenger follow-up programs. We find that, while a significant fraction of the explosion energy can be emitted in the infrared-optical-ultraviolet (UVOIR) band, the optical signal alone is not optimal for neutrino searches. Rather, the neutrino emission is strongly correlated with the one in the radio band, if a dense circumstellar medium surrounds the transient, and with X-rays tracking the activity of the central engine. Joint observations of transients in radio, X-rays, and neutrinos will crucially complement those in the UVOIR band, breaking degeneracies in the transient parameter space. Our findings call for heightened surveys in the radio and X-ray bands to warrant multi-messenger detections.

Authors:Nafisa Aftab, Biswajit Paul

Abstract: Eclipsing X-ray binaries make an ideal condition to study reprocessed X-rays, as the X-rays detected during eclipse are purely reprocessed while the much brighter primary X-rays are blocked by the companion star. We carried out a comprehensive study of X-ray reprocessing with four eclipsing Low Mass X-ray Binary (LMXB) systems by comparing X-ray spectra during and outside eclipse with \textit{XMM-Newton} EPIC pn observations. The 17 observations of MXB 1659$-$298, AX J1745.6$-$2901, EXO 0748$-$676 and XTE J1710$-$281 give unique features of the systems. For example, X-ray reprocessing characteristics in AX J1745.6$-$2901 is found to be nearly same irrespective of the intensity state; there is an indication of different types of variable warp structures in the inner accretion disk in EXO 0748$-$676, a high out-of-eclipse to eclipse flux ratio in XTE J1710$-$281 inspite of a large size of the accretion disk perhaps indicates low scale height of the accretion disk. The eclipse spectra for some of the LMXB sources are reported for the first time. We have derived the fractional visible area of the accretion disk during maximum eclipse phase for various obscuration geometries. The out-of-eclipse to eclipse flux ratio in LMXBs observed to be smaller compared to that found in High Mass X-ray Binaries. This indicates greater reprocessing in LMXBs despite having less dense, less extended stellar wind from the companion. The X-ray reprocessing efficiencies observed in LMXBs indicate large dependencies of X-ray reprocessing on the scale height of the accretion disk, relative size of the disk compared to the companion and some other unknown factors.

Authors:Sumeet Kulkarni, Surendra Padamata, Anuradha Gupta, David Radice, Rahul Kashyap

Abstract: We present, for the first time, recoil velocity estimates for binary neutron star mergers using data from numerical relativity simulations. We find that binary neutron star merger remnants can have recoil velocity of the order of a few tens of km/s and as high as $150$ km/s in our dataset. These recoils are attained due to equivalent contributions from the anisotropic gravitational wave emission as well as the asymmetric ejection of dynamical matter during the merger. We provide fits for net recoil velocity as well as its ejecta component as a function of the amount of ejected matter, which may be useful when constraints on the ejected matter are obtained through electromagnetic observations. We also estimate the mass and spin of the remnants and find them to be in the range $[2.34, 3.38] M_{\odot}$ and $[0.63, 0.82]$ respectively, for our dataset.

Authors:Frank McNally for the IceCube Collaboration, Rasha Abbasi for the IceCube Collaboration, Paolo Desiati for the IceCube Collaboration, Juan Carlos Díaz Vélez for the IceCube Collaboration, Christina Cochling for the IceCube Collaboration, Katherine Gruchot for the IceCube Collaboration, William Hayes for the IceCube Collaboration, Andrew Moy for the IceCube Collaboration, Emily Schmidt for the IceCube Collaboration, Andrew Thorpe for the IceCube Collaboration

Abstract: The IceCube Observatory provides our highest-statistics picture of the cosmic-ray arrival directions in the Southern Hemisphere, with over 700 billion cosmic-ray-induced muon events collected between May 2011 and May 2022. Using the larger data volume, we find an improved significance of the PeV cosmic ray anisotropy down to scales of $6^\circ$. In addition, we observe a variation in the angular power spectrum as a function of energy, hinting at a relative decrease in large-scale features above 100 TeV. The data-taking period covers a complete solar cycle, providing new insight into the time variability of the signal. We present preliminary results using this up-to-date event sample.

Authors:Andrew King

Abstract: I consider the current sample of galaxy nuclei producing quasiperiodic eruptions (QPEs). If the quasiperiod results from the orbital motion of a star around the central black hole, the dearth of associated black hole masses $\gtrsim 10^6\msun$ places tight constraints on models. It disfavours those assuming wide orbits and small eccentricities, because there is ample volume within pericentre to allow significantly more massive holes in QPE systems than are currently observed. If instead the orbiting star is assumed to pass close to the black hole, the same lack of large black hole masses strongly suggests that the stellar orbits must be significantly eccentric, with $1 - e \lesssim {\rm few}\times 10^{-2}$. This favours a tidal disruption near-miss picture where QPEs result from repeated accretion from an orbiting star (in practice a white dwarf) losing orbital angular momentum to gravitational radiation, even though this is not assumed in deriving the eccentricity constraint. Given the tight constraints resulting from the current small observed sample, attempts to find QPE systems in more massive galaxies are clearly important.

Authors:Garvin Yim, Yong Gao, Yacheng Kang, Lijing Shao, Renxin Xu

Abstract: Gravitational waves from isolated sources have eluded detection so far. The upper limit of long-lasting continuous gravitational wave emission is now at the stage of probing physically-motivated models with the most optimistic being strongly constrained. One potential avenue to remedy this is to relax the assumption of the gravitational wave being quasi-infinite in duration, leading to the idea of transient continuous gravitational waves. In this paper, we outline how to get transient continuous waves from magnetars (or strongly-magnetised neutron stars) that exhibit glitches and/or antiglitches. We put forward a toy model whereby at a glitch or antiglitch, mass is ejected from the magnetar but becomes trapped on its outward journey through the magnetosphere. Depending on the specific values of the height of the trapped ejecta and the magnetic inclination angle, we are able to reproduce both glitches and antiglitches from simple angular momentum arguments. The trapped ejecta sets the magnetar into precession causing gravitational waves to be emitted at once and twice the magnetar's spin frequency, for a duration equal to however long the ejecta is trapped for. We find that the gravitational waves are more likely to be detectable when the magnetar is: closer, rotating faster, or has larger glitches/antiglitches. Specific to this model, we find that the detectability improves when the ejecta height and magnetic inclination angle have values near the boundary in the parameter space that separates glitches and antiglitches, though this requires more mass to be ejected to remain consistent with the observed glitch/antiglitch.

Authors:Lucas Guillemot, Ismaël Cognard, Willem van Straten, Gilles Theureau, Eric Gérard

Abstract: Accurate polarimetric calibration of the radio pulse profiles from pulsars is crucial for studying their radiation properties at these wavelengths. Inaccurate calibration can also distort recorded pulse profiles, introducing noise in time of arrival (TOA) data and thus degrading pulsar timing analyses. One method for determining the full polarimetric response of a given telescope is to conduct observations of bright polarized pulsars over wide ranges of parallactic angles, to sample different orientations of their polarization angle and determine the cross-couplings between polarization feeds. The Nan\c{c}ay decimetric Radio Telescope (NRT) is a 94m equivalent meridian telescope, capable of tracking a given pulsar for approximately one hour around transit. In November 2019, we began conducting regular observations of the bright and highly linearly polarized pulsar PSR~J0742$-$2822, in a special mode where the feed horn rotates by $\sim 180^\circ$ over the course of the one hour observation, mimicking wide parallactic angle variations and enabling us to determine the polarimetric response of the NRT at 1.4~GHz. The improved polarimetric response of the NRT as determined from these observations was applied to observations of a selection of MSPs with published polarimetric properties. We find that the new polarimetric profiles and polarization position angles are consistent with previous findings, unlike NRT polarimetric results obtained with the previously used method of calibration. The analysis of timing data on J1730$-$2304, J1744$-$1134, and J1857+0953 shows that the new calibration method improves the quality of the timing, and the Matrix Template Matching (MTM) method proves very effective at reducing noise from imperfect calibration. For pulsars with sufficient degrees of polarization, the MTM method appears to be the preferred method for extracting TOAs from NRT observations.

Authors:Ling-Jun Guo, Wen-Cong Yang, Yong-Liang Ma, Yue-Liang Wu

Abstract: The cores of massive neutron stars provide a unique environment for the dense nuclear matter in the universe. The global properties of a neutron star and gravitational waves emitted from the binary neutron star merger carry information about dense nuclear matter. We study in this paper the effect of the possible hadron-quark transition on the properties of the neutron star and the gravitational waves emitted from the binary neutron star merger by using the equations of state constructed from the Maxwell ansatz, Gibbs ansatz and, the crossover scenario. Our results show that the short period of the inspiral phase and the earlier collapse to a black hole indicate a soft equation of state. In combination with the future detection of the $10$kHz gravitational waves emitted from the binary neutron star merger and the signals from the electromagnetic counterparts, we expect the present study could reveal some characters of the dense nuclear matter.

Authors:Sudip Chakraborty, Ajay Ratheesh, Francesco Tombesi, Rodrigo Nemmen, Srimanta Banerjee

Abstract: Through their radio loudness, lack of thermal UV emission from the accretion disk and power-law dominated spectra, Low Luminosity AGN (LLAGN) display similarity with the hard state of stellar-mass black hole X-Ray Binaries (BHBs). In this work we perform a systematic hard X-ray spectral study of a carefully selected sample of unobscured LLAGN using archival $NuSTAR$ data, to understand the central engine properties in the lower accretion regime. We analyze the $NuSTAR$ spectra of a sample of 16 LLAGN. We model the continuum emission with detailed Comptonization models. We find a strong anti-correlation between the optical depth and the electron temperature of the corona, previously also observed in the brighter Seyferts. This anti-correlation is present irrespective of the shape of the corona, and the slope of this anti-correlation in the log space for LLAGN (0.68-1.06) closely matches that of the higher accretion rate Seyferts (0.55-1.11) and hard state of BHBs ($\sim$0.87). This anti-correlation may indicate a departure from a fixed disk-corona configuration in radiative balance. Our result, therefore, demonstrates a possible universality in Comptonization processes of black hole X-ray sources across multiple orders of magnitude in mass and accretion rate.

Authors:Spencer Griswold for the IceCube Collaboration, Segev BenZvi for the IceCube Collaboration

Abstract: The next Galactic core-collapse supernova (CCSN) presents a once-in-a-lifetime opportunity to make astrophysical measurements using neutrinos, gravitational waves, and electromagnetic radiation. CCSNe local to the Milky Way are extremely rare, so it is paramount that detectors are prepared to observe the signal when it arrives. The IceCube Neutrino Observatory, a gigaton water Cherenkov detector below the South Pole, is sensitive to the burst of neutrinos released by a Galactic CCSN at a level $>$10$\sigma$. This burst of neutrinos precedes optical emission by hours to days, enabling neutrinos to serve as an early warning for follow-up observation. IceCube's detection capabilities make it a cornerstone of the global network of neutrino detectors monitoring for Galactic CCSNe, the SuperNova Early Warning System (SNEWS 2.0). In this contribution, we describe IceCube's sensitivity to Galactic CCSNe and strategies for operational readiness, including "fire drill" data challenges. We also discuss coordination with SNEWS 2.0.

Authors:Mauri J. Valtonen, Lankeswar Dey, Achamveedu Gopakumar, Staszek Zola, Anne Lähteenmäki, Merja Tornikoski, Alok C. Gupta, Tapio Pursimo, Emil Knudstrup, Jose L. Gomez, Rene Hudec, Martin Jelínek, Jan Štrobl, Andrei V. Berdyugin, Stefano Ciprini, Daniel E. Reichart, Vladimir V. Kouprianov, Katsura Matsumoto, Marek Drozdz, Markus Mugrauer, Alberto Sadun, Michal Zejmo, Aimo Sillanpää, Harry J. Lehto, Kari Nilsson, Ryo Imazawa, Makoto Uemura

Abstract: We present a summary of the results of the OJ 287 observational campaign, which was carried out during the 2021/2022 observational season. This season is special in the binary model because the major axis of the precessing binary happens to lie almost exactly in the plane of the accretion disc of the primary. This leads to pairs of almost identical impacts between the secondary black hole and the accretion disk in 2005 and 2022. In 2005, a special flare called "blue flash" was observed 35 days after the disk impact, which should have also been verifiable in 2022. We did observe a similar flash and were able to obtain more details of its properties. We describe this in the framework of expanding cloud models. In addition, we were able to identify the flare arising exactly at the time of the disc crossing from its photo-polarimetric and gamma-ray properties. This is an important identification, as it directly confirms the orbit model. Moreover, we saw a huge flare that lasted only one day. We may understand this as the lighting up of the jet of the secondary black hole when its Roche lobe is suddenly flooded by the gas from the primary disk. Therefore, this may be the first time we directly observed the secondary black hole in the OJ 287 binary system.

Authors:Felix Schlüter for the IceCube-Gen2 Collaboration, Simona Toscano for the IceCube-Gen2 Collaboration

Abstract: The IceCube-Gen2 Neutrino Observatory is proposed to extend the all-flavour energy range of IceCube beyond PeV energies. It will comprise two key components: I) An enlarged 8$\,$km$^3$ in-ice optical Cherenkov array to measure the continuation of the IceCube astrophysical neutrino flux and improve IceCube's point source sensitivity above $\sim\,$100$\,$TeV; and II) A very large in-ice radio array with a surface area of about 500$\,$km$^2$. Radio waves propagate through ice with a kilometer-long attenuation length, hence a sparse radio array allows us to instrument a huge volume of ice to achieve a sufficient sensitivity to detect neutrinos with energies above tens of PeV. The different signal topologies for neutrino-induced events measured by the optical and in-ice radio detector - the radio detector is mostly sensitive to the cascades produced in the neutrino interaction, while the optical detector can detect long-ranging muon and tau leptons with high accuracy - yield highly complementary information. When detected in coincidence, these signals will allow us to reconstruct the neutrino energy and arrival direction with high fidelity. Furthermore, if events are detected in coincidence with a sufficient rate, they resemble the unique opportunity to study systematic uncertainties and to cross-calibrate both detector components. We present the expected rate of coincidence events for 10 years of operation. Furthermore, we analyzed possible detector optimizations to increase the coincidence rate.

Authors:Randall Rojas Bolivar, Daniel Wik, Ayşegül Tümer, Fabio Gastaldello, Julie Hlavacek-Larrondo, Paul Nulsen, Valentina Vacca, Grzegorz Madejski, Ming Sun, Craig Sarazin, Jeremy Sanders, Damiano Caprioli, Brian Grefenstette, Niels-Jorgen Westergaard

Abstract: Observations from past missions such as RXTE and Beppo-SAX suggested the presence of inverse Compton (IC) scattering at hard X-ray energies within the intracluster medium of some massive galaxy clusters. In subsequent years, observations by, e.g., Suzaku, and now NuSTAR, have not been able to confirm these detections. We report on NuSTAR hard X-ray searches for IC emission in two massive galaxy clusters, Abell 665 and Abell 2146. To constrain the global IC flux in these two clusters, we fit global NuSTAR spectra with three models: single (1T) and two-temperature (2T) models, and a 1T plus power law component (T$+$IC). The temperature components are meant to characterize the thermal ICM emission, while the power law represents the IC emission. We find that the 3-30 keV Abell 665 and 3-20 keV Abell 2146 spectra are best described by thermal emission alone, with average global temperatures of $kT = (9.15\pm 0.1)$ keV for Abell 665 and $kT = (8.29\pm 0.1)$ keV for Abell 2146. We constrain the IC flux to $F_{\rm NT} < 0.60 \times 10^{-12}$ erg s$^{-1}$ cm$^{-2}$ and $F_{\rm NT} < 0.85 \times 10^{-12}$ erg s$^{-1}$ cm$^{-2}$ (20-80 keV) for Abell 665 and Abell 2146, respectively both at the 90% confidence level. When we couple the IC flux limits with 1.4 GHz diffuse radio data from the VLA, we set lower limits on the average magnetic field strengths of $>$0.14 $\mu$G and $>$0.011 $\mu$G for Abell 665 and Abell 2146, respectively.

Authors:T. Nagao, F. Patat, A. Cikota, D. Baade, S. Mattila, R. Kotak, H. Kuncarayakti, M. Bulla, B. Ayala

Abstract: The explosion processes of supernovae (SNe) are imprinted in their explosion geometries. Here, we study the intrinsic polarization of 15 hydrogen-rich core-collapse SNe and explore the relation with the photometric and spectroscopic properties. Our sample shows diverse properties of the continuum polarization. The polarization of most SNe has a low degree at early phases but shows a sudden rise to $\sim 1$ \% degree at certain points during the photospheric phase as well as a slow decline during the tail phase, with a constant polarization angle. The variation in the timing of peak polarisation values implies diversity in the explosion geometry: some SNe have aspherical structures only in their helium cores, while in other SNe these reach out to a significant part of the outer hydrogen envelope with a common axis from the helium core to the hydrogen envelope. Other SNe show high polarization from early phases and a change of the polarization angle around the middle of the photospheric phase. This implies that the ejecta are significantly aspherical to the outermost layer and have multi-directional aspherical structures. Exceptionally, the Type~IIL SN~2017ahn shows low polarization at both the photospheric and tail phases. Our results show that the timing of the polarization rise in Type~IIP SNe is likely correlated with their brightness, velocity and the amount of radioactive Ni produced: brighter SNe with faster ejecta velocity and a larger $^{56}$Ni mass have more extended-aspherical explosion geometries. In particular, there is a clear correlation between the timing of the polarization rise and the explosion energy, that is, the explosion asphericity is proportional to the explosion energy. This implies that the development of a global aspherical structure, e.g., a jet, might be the key to realising an energetic SN in the mechanism of SN explosions.

Authors:Jun Yang SEE, Chalmers University of Technology, Sweden, Federico García Instituto Argentino de Radioastronomía, Argentina, Santiago del Palacio SEE, Chalmers University of Technology, Sweden, Ralph Spencer Jodrell Bank Centre for Astrophysics, UK, Zsolt Paragi JIVE, The Netherlands, Noel Castro Segura University of Southampton, UK, Biping Gong Huazhong University of Science and Technology, China, Hongmin Cao Shangqiu Normal University, China, Wen Chen Yunnan Observatories, China

Abstract: Cygnus X-3 is a high-mass X-ray binary with a compact object accreting matter from a Wolf-Rayet donor star. Recently, it has been revealed by the Imaging X-ray Polarimetry Explorer (IXPE) as a hidden Galactic ultra-luminous X-ray (ULX) source with a luminosity above the Eddington limit along the direction of a narrow (opening angle <~32 degree) funnel. In between the IXPE observations, we observed Cyg X-3 with the European VLBI (very long baseline interferometry) Network at 22 GHz and the NICER X-ray instrument. To probe possible relations between the X-ray funnel and the potential radio jet from the ULX, we analyzed the simultaneous multi-wavelength data. Our high-resolution VLBI image reveals an elongated structure with a position angle of -3.2+/-0.4 degree, accurately perpendicular to the direction of the linear X-ray polarization. Because Cyg X-3 was in the radio quiescent state on 2022 November 10, we identify the mas-scale structure as the innermost radio jet. The finding indicates that the radio jet propagates along and within the funnel. Moreover, the jet is marginally resolved in the transverse direction. This possibly results from the strong stellar winds and the rapid orbital motion of the binary system.

Authors:Massimiliano Lincetto for the IceCube Collaboration, Eric Evans-Jacquez for the IceCube Collaboration, Benedikt Riedel for the IceCube Collaboration, David Schultz for the IceCube Collaboration, Tianlu Yuan for the IceCube Collaboration

Abstract: The IceCube realtime alert system has been operating since 2016. It provides prompt alerts on high-energy neutrino events to the astroparticle physics community. The localization regions for the incoming direction of neutrinos are published through NASA's Gamma-ray Coordinate Network (GCN). The IceCube realtime system consists of infrastructure dedicated to the selection of alert events, the reconstruction of their topology and arrival direction, the calculation of directional uncertainty contours and the distribution of the event information through public alert networks. Using a message-based workflow management system, a dedicated software (SkyDriver) provides a representational state transfer (REST) interface to parallelized reconstruction algorithms. In this contribution, we outline the improvements of the internal infrastructure of the IceCube realtime system that aims to streamline the internal handling of neutrino events, their distribution to the SkyDriver interface, the collection of the reconstruction results as well as their conversion into human- and machine-readable alerts to be publicly distributed through different alert networks. An approach for the long-term storage and cataloging of alert events according to findability, accessibility, interoperability and reusability (FAIR) principles is outlined.

Authors:T. P. Roberts Durham-CEA, D. J. Walton Hertfordshire, A. D. A. Mackenzie Durham-CEA, M. Heida ESO, S. Scaringi Durham-CEA

Abstract: A prime motivation for compiling catalogues of any celestial X-ray source is to increase our numbers of rare sub-classes. In this work we take a recent multi-mission catalogue of ultraluminous X-ray sources (ULXs) and look for hitherto poorly-studied ULX candidates that are luminous ($L_{\rm X} \geq 10^{40} \rm ~erg~s^{-1}$), bright ($f_{\rm X} \geq 5 \times 10^{-13} \rm ~erg~cm~s^{-1}$) and have archival XMM-Newton data. We speculate that this luminosity regime may be ideal for identifying new pulsating ULXs (PULXs), given that the majority of known PULXs reach similar high luminosities. We find three sources that match our criteria, and study them using archival data. We find 4XMM J165251.5-591503 to possess a bright and variable Galactic optical/IR counterpart, and so conclude it is very likely to be a foreground interloper. 4XMM J091948.8-121429 does appear an excellent ULX candidate associated with the dwarf irregular galaxy PGC 26378, but has only one detection to date with low data quality. The best dataset belongs to 4XMM J112054.3+531040 which we find to be a moderately variable, spectrally hard ($\Gamma \approx 1.4$) X-ray source located in a spiral arm of NGC 3631. Its spectral hardness is similar to known PULXs, but no pulsations are detected by accelerated pulsation searches in the available data. We discuss whether other missions provide objects for similar studies, and compare this method to others suggested for identifying good PULX candidates.

Authors:Massimiliano Lincetto for the IceCube Collaboration

Abstract: The sources of the astrophysical neutrino flux discovered by IceCube are for the most part unresolved. Extragalactic core-collapse supernovae (CCSNe) have been suggested as candidate multi-messenger sources. In interaction-powered supernovae, a shock propagates in a dense circumstellar medium (CSM), producing a bright optical emission and potentially accelerating particles to relativistic energies. Shock interaction is believed to be the main energy source for Type IIn supernovae (identified by narrow lines in the spectrum), hydrogen-rich superluminous supernovae and a subset of hydrogen-poor superluminous supernovae. Production of high-energy neutrinos is expected in collisions between the accelerated protons in the shocks and the cold CSM particles. We select a catalog of interaction-powered supernovae from the Bright Transient Survey of the Zwicky Transient Facility. We exploit a novel modeling effort that connects the time evolution of the optical emission to the properties of the ejecta and the CSM, allowing us to set predictions of the neutrino flux for each source. In this contribution, we describe a stacking search for high-energy neutrinos from this population of CCSNe with the IceCube Neutrino Observatory.

Authors:Markus Boettcher North-West University, Potchefstroom, South Africa

Abstract: In the light of growing evidence that blazars are responsible for part of the astrophysical very-high-energy neutrino flux detected by IceCube, models for neutrino production through photo-pion interactions in blazar jets have been developed. Evidence is also mounting that photon fields originating external to the jet are strongly favored over the co-moving primary electron synchrotron photon field as target for photo-pion interactions. Even though those external photon fields appear highly anisotropic in the co-moving frame of the emission region, current models usually consider neutrino production to occur isotropically in the co-moving frame, resulting in a beaming pattern that is identical to intrinsically isotropic synchrotron and synchrotron self-Compton emission. In this paper, we derive the resulting beaming patterns of neutrinos produced by interactions wich external photon fields, taking into account all relevant anisotropy effects. It is shown that neutrino emission resulting from photo-pion production on a stationary and isotropic (in the AGN rest frame) external photon field is significantly more strongly beamed along the jet direction than intrinsically isotropic emission. For the most highly beamed sources, this implies that expected neutrino fluxes are grossly under-estimated or jet-power requirements for the production of a given neutrino flux grossly over-estimated when not accounting for the proper Doppler boosting and beaming characteristics.

Authors:IceCube Collaboration

Abstract: The IceCube Neutrino Observatory has been continuously taking data to search for O(0.5-10) s long neutrino bursts since 2007. Even if a Galactic core-collapse supernova is optically obscured or collapses to a black hole instead of exploding, it will be detectable via the O(10) MeV neutrino burst emitted during the collapse. We discuss a search for such events covering the time between April 17, 2008 and December 31, 2019. Considering the average data taking and analysis uptime of 91.7% after all selection cuts, this is equivalent to 10.735 years of continuous data taking. In order to test the most conservative neutrino production scenario, the selection cuts were optimized for a model based on a 8.8 solar mass progenitor collapsing to an O-Ne-Mg core. Conservative assumptions on the effects of neutrino oscillations in the exploding star were made. The final selection cut was set to ensure that the probability to detect such a supernova within the Milky Way exceeds 99%. No such neutrino burst was found in the data after performing a blind analysis. Hence, a 90% C.L. upper limit on the rate of core-collapse supernovae out to distances of ~ 25kpc was determined to be 0.23/yr. For the more distant Magellanic Clouds, only high neutrino luminosity supernovae will be detectable by IceCube, unless external information on the burst time is available. We determined a model-independent limit by parameterizing the dependence on the neutrino luminosity and the energy spectrum.

Authors:Roberto Turolla, Roberto Taverna, Gian Luca Israel, Fabio Muleri, Silvia Zane, Matteo Bachetti, Jeremy Heyl, Alessandro Di Marco, Ephraim Gau, Henric Krawczynski, Mason Ng, Andrea Possenti, Juri Poutanen, Luca Baldini, Giorgio Matt, Michela Negro, Ivan Agudo, Lucio Angelo Antonelli, Wayne H. Baumgartner, Ronaldo Bellazzini, Stefano Bianchi, Stephen D. Bongiorno, Raffaella Bonino, Alessandro Brez, Niccolo' Bucciantini, Fiamma Capitanio, Simone Castellano, Elisabetta Cavazzuti, Chien-Ting J. Chen, Stefano Ciprini, Enrico Costa, Alessandra De Rosa, Ettore Del Monte, Laura Di Gesu, Niccolo' Di Lalla, Immacolata Donnarumma, Victor Doroshenko, Michal Doviak, Steven R. Ehlert, Teruaki Enoto, Yuri Evangelista, Sergio Fabiani, Riccardo Ferrazzoli, Javier A. Garcia, Shuichi Gunji, Kiyoshi Hayashida, Wataru Iwakiri, Svetlana G. Jorstad, Philip Kaaret, Vladimir Karas, Fabian Kislat, Takao Kitaguchi, Jeffrey Kolodziejczak, Fabio La Monaca, Luca Latronico, Ioannis Liodakis, Simone Maldera, Alberto Manfreda, Frederic Marin, Andrea Marinucci, Alan P. Marscher, Herman L. Marshall, Francesco Massaro, Ikuyuki Mitsuishi, Tsunefumi Mizuno, Stephen Chi-Yung Ng, Stephen L. O'Dell, Nicola Omodei, Chiara Oppedisano, Alessandro Papitto, George G. Pavlov, Abel L. Peirson, Matteo Perri, Melissa Pesce-Rollins, Pierre-Olivier Petrucci, Maura Pilia, Simonetta Puccetti, Brian Ramsey, John Rankin, Ajay Ratheesh, Oliver J. Roberts, Roger W. Romani, Carmelo Sgro', Patrick Slane, Paolo Soffitta, Gloria Spandre, Douglas A. Swartz, Toru Tamagawa, Fabrizio Tavecchio, Yuzuru Tawara, Allyn F. Tennant, N. Thomas, Francesco Tombesi, Alessio Trois, Sergey S. Tsygankov, Jacco Vink, Martin C. Weisskopf, Kinwah Wu, Fei Xie

Abstract: Recent observations with the Imaging X-ray Polarimetry Explorer (IXPE) of two anomalous X-ray pulsars provided evidence that X-ray emission from magnetar sources is strongly polarized. Here we report on the joint IXPE and XMM-Newton observations of the soft {\gamma}-repeater SGR 1806-20. The spectral and timing properties of SGR 1806-20 derived from XMM-Newton data are in broad agreement with previous measurements; however, we found the source at an all-time-low persistent flux level. No significant polarization was measured apart from the 4-5 keV energy range, where a probable detection with PD=31.6\pm 10.5% and PA=-17.6\pm 15 deg was obtained. The resulting polarization signal, together with the upper limits we derive at lower and higher energies 2-4 and 5-8 keV, respectively) is compatible with a picture in which thermal radiation from the condensed star surface is reprocessed by resonant Compton scattering in the magnetosphere, similar to what proposed for the bright magnetar 4U 0142+61.

Authors:Sarah Louisa Pitz, Jürgen Schaffner-Bielich

Abstract: The properties of selfinteracting boson stars with different scalar potentials going beyond the commonly used $\phi^4$ ansatz are studied. The scalar potential is extended to different values of the exponent $n$ of the form $V \propto \phi^n$. Two stability mechanism for boson stars are introduced, the first being a mass term and the second one a vacuum term. We present analytic scale-invariant expressions for these two classes of equations of state. The resulting properties of the boson star configurations differ considerably from previous calculations. We find three different categories of mass-radius relation: the first category resembles the mass-radius curve of selfbound stars, the second one those of neutron stars and the third one is the well known constant radius case from the standard $\phi^4$ potential. We demonstrate that the maximal compactness can reach extremely high values going to the limit of causality $C_\text{max} = 0.354$ asymptotically for $n\to\infty$. The maximal compactnesses exceed previously calculated values of $C_\text{max}=0.16$ for the standard $\phi^4$-theory and $C_\text{max}=0.21$ for vector-like interactions and is in line with previous results for solitonic boson stars. Hence, boson stars even described by a simple modified scalar potential in the form of $V \propto \phi^n$ can be ultra compact black hole mimickers where the photon ring is located outside the radius of the star.

Authors:Jiaying Xu, Yi Feng, Di Li, Pei Wang, Yongkun Zhang, Jintao Xie, Huaxi Chen, Han Wang, Zhixuan Kang, Jingjing Hu, Yun Zheng, Chao-Wei Tsai, Xianglei Chen, Dengke Zhou

Abstract: The volume of research on fast radio bursts (FRBs) observation have been seeing a dramatic growth. To facilitate the systematic analysis of the FRB population, we established a database platform, Blinkverse (https://blinkverse.alkaidos.cn), as a central inventory of FRBs from various observatories and with published properties, particularly dynamic spectra from FAST, CHIME, GBT, Arecibo, etc. Blinkverse thus not only forms a superset of FRBCAT, TNS, and CHIME/FRB, but also provides convenient access to thousands of FRB dynamic spectra from FAST, some of which were not available before. Blinkverse is regularly maintained and will be updated by external users in the future. Data entries of FRBs can be retrieved through parameter searches through FRB location, fluence, etc., and their logical combinations. Interactive visualization was built into the platform. We analyzed the energy distribution, period analysis, and classification of FRBs based on data downloaded from Blinkverse. The energy distributions of repeaters and non-repeaters are found to be distinct from one another.

Authors:Anastasiya Yilmaz, Jiri Svoboda, Victoria Grinberg, Peter G. Boorman, Michal Bursa, Michal Dovciak

Abstract: Black hole X-ray binaries are ideal environments to study the accretion phenomena in strong gravitational potentials. These systems undergo dramatic accretion state transitions and analysis of the X-ray spectra is used to probe the properties of the accretion disc and its evolution. In this work, we present a systematic investigation of $\sim$1800 spectra obtained by RXTE PCA observations of GRO J1655-40 and LMC X-3 to explore the nature of the accretion disc via non-relativistic and relativistic disc models describing the thermal emission in black-hole X-ray binaries. We demonstrate that the non-relativistic modelling throughout an outburst with the phenomenological multi-colour disc model DISKBB yields significantly lower and often unphysical inner disc radii and correspondingly higher ($\sim$50-60\%) disc temperatures compared to its relativistic counterparts KYNBB and KERRBB. We obtained the dimensionless spin parameters of $a_{*}=0.774 \pm 0.069 $ and $a_{*}=0.752 \pm 0.061 $ for GRO J1655-40 with KERRBB and KYNBB, respectively. We report a spin value of $a_{*}=0.098 \pm 0.063$ for LMC X-3 using the updated black hole mass of 6.98 ${M_{\odot}}$. Both measurements are consistent with the previous studies. Using our results, we highlight the importance of self-consistent modelling of the thermal emission, especially when estimating the spin with the continuum-fitting method which assumes the disc terminates at the innermost stable circular orbit at all times.

Authors:Sk. Minhajur Rahaman, Jonathan Granot, Paz Beniamini

Abstract: Internal shocks are a leading candidate for the dissipation mechanism that powers the prompt $\gamma$-ray emission in gamma-ray bursts (GRBs). In this scenario a compact central source produces an ultra-relativistic outflow with varying speeds, causing faster parts or shells to collide with slower ones. Each collision produces a pair of shocks -- a forward shock (FS) propagating into the slower leading shell and a reverse shock (RS) propagating into the faster trailing shell. The RS's lab-frame speed is always smaller, while the RS is typically stronger than the FS, leading to different conditions in the two shocked regions that both contribute to the observed emission. We show that optically-thin synchrotron emission from both (weaker FS + stronger RS) can naturally explain key features of prompt GRB emission such as the pulse shapes, time-evolution of the $\nu{}F_\nu$ peak flux and photon-energy, and the spectrum. Particularly, it can account for two features commonly observed in GRB spectra: (i) a sub-dominant low-energy spectral component (often interpreted as ``photospheric''-like), or (ii) a doubly-broken power-law spectrum with the low-energy spectral slope approaching the slow cooling limit. Both features can be obtained while maintaining high overall radiative efficiency without any fine-tuning of the physical conditions.

Authors:Ludwig M. Böss, Ulrich P. Steinwandel, Klaus Dolag

Abstract: Non-thermal emission from relativistic electrons gives insight into the strength and morphology of intra-cluster magnetic fields, as well as providing powerful tracers of structure formation shocks. Emission caused by Cosmic Ray (CR) protons on the other hand still challenges current observations and is therefore testing models of proton acceleration at intra-cluster shocks. Large-scale simulations including the effects of CRs have been difficult to achieve and have been mainly reduced to simulating an overall energy budget, or tracing CR populations in post-processing of simulation output and has often been done for either protons or electrons. We use an efficient on-the-fly Fokker-Planck solver to evolve distributions of CR protons and electrons within every resolution element of our simulation. The solver accounts for CR acceleration at intra-cluster shocks, based on results of recent PIC simulations, re-acceleration due to shocks and MHD turbulence, adiabatic changes and radiative losses of electrons. We apply this model to zoom simulations of galaxy clusters, recently used to show the evolution of the small-scale turbulent dynamo on cluster scales. For these simulations we use a spectral resolution of 48 bins over 6 orders of magnitude in momentum for electrons and 12 bins over 6 orders of magnitude in momentum for protons. We present preliminary results about a possible formation mechanism for Wrong Way Radio Relics in our simulation.

Authors:Deheng Song, Kohta Murase, Ali Kheirandish

Abstract: Galaxy clusters are promising targets for indirect detection of dark matter thanks to the large dark matter content. Using 14 years of Fermi-LAT data from seven nearby galaxy clusters, we obtain constraints on the lifetime of decaying very heavy dark matter particles with masses ranging from $10^3$ GeV to $10^{16}$ GeV. We consider a variety of decaying channels and calculate prompt gamma rays and electrons/positrons from the dark matter. Furthermore, we take into account electromagnetic cascades induced by the primary gamma rays and electrons/positrons, and search for the resulting gamma-ray signals from the directions of the galaxy clusters. We adopt a Navarro-Frenk-White profile of the dark matter halos, and use the profile likelihood method to set lower limits on the dark matter lifetime at a 95% confidence level. Our results are competitive with those obtained through other gamma-ray observations of galaxy clusters and provide complementary constraints to existing indirect searches for decaying very heavy dark matter.

Authors:James H. Gillanders, Eleonora Troja, Chris L. Fryer, Marko Ristic, Brendan O'Connor, Christopher J. Fontes, Yu-Han Yang, Nanae Domoto, Salma Rahmouni, Masaomi Tanaka, Ori D. Fox, Simone Dichiara

Abstract: Kilonovae are a novel class of astrophysical transients, and the only observationally-confirmed site of rapid neutron capture nucleosynthesis (the r-process) in the Universe. To date, only a handful of kilonovae have been detected, with just a single spectroscopically-observed event (AT 2017gfo). Spectra of AT 2017gfo provided evidence for the formation of elements heavier than iron; however, these spectra were collected during the first ~ 10 days, when emission from light r-process elements dominates the observations. Heavier elements, if synthesised, are expected to shape the late-time evolution of the kilonova, beyond the phases for which we have spectral observations. Here we present spectroscopic observations of a rapidly-reddening thermal transient, following the gamma-ray burst, GRB 230307A. Early (2.4 day) optical spectroscopy identifies the presence of a hot (T ~ 6700 K) thermal continuum. By 29 days, this component has expanded and cooled significantly (T ~ 640 K), yet it remains optically thick, indicating the presence of high-opacity ejecta. We show that these properties can only be explained by the merger of compact objects, and further, leads us to infer the production of the heavy lanthanide elements. We identify several spectral features (in both absorption and emission), whose cause can be explained by newly-synthesised heavy elements. This event marks only the second recorded spectroscopic evidence for the synthesis of r-process elements, and the first to be observed at such late times.

Authors:Yu-Han Yang, Eleonora Troja, Brendan O'Connor, Chris L. Fryer, Myungshin Im, Joe Durbak, Gregory S. H. Paek, Roberto Ricci, Clécio R. De Bom, James H. Gillanders, Alberto J. Castro-Tirado, Zong-Kai Peng, Simone Dichiara, Geoffrey Ryan, Hendrik van Eerten, Zi-Gao Dai, Seo-Won Chang, Hyeonho Choi, Kishalay De, Youdong Hu, Charles D. Kilpatrick, Alexander Kutyrev, Mankeun Jeong, Chung-Uk Lee, Martin Makler, Felipe Navarrete, Ignacio Pérez-García

Abstract: Kilonovae are a rare class of astrophysical transients powered by the radioactive decay of nuclei heavier than iron, synthesized in the merger of two compact objects. Over the first few days, the kilonova evolution is dominated by a large number of radioactive isotopes contributing to the heating rate. On timescales of weeks to months, its behavior is predicted to differ depending on the ejecta composition and merger remnant. However, late-time observations of known kilonovae are either missing or limited. Here we report observations of a luminous red transient with a quasi-thermal spectrum, following an unusual gamma-ray burst of long duration. We classify this thermal emission as a kilonova and track its evolution up to two months after the burst. At these late times, the recession of the photospheric radius and the rapidly-decaying bolometric luminosity ($L_{\rm bol}\propto t^{-2.7\pm 0.4}$) support the recombination of lanthanide-rich ejecta as they cool.

Authors:M. Parra, P. -O. Petrucci, S. Bianchi, V. E. Gianolli, F. Ursini, G. Ponti

Abstract: The presence of blueshifted absorption lines in the X-ray spectra of Black Hole Low Mass X-ray Binaries is the telltale of massive outflows called winds. These signatures are found almost exclusively in soft states of high-inclined systems, hinting at equatorial ejections originating from the accretion disk and deeply intertwined with the evolution of the outburst patterns displayed by these systems. In the wake of the launch of the new generation of X-ray spectrometers, studies of wind signatures remain mostly restricted to single sources and outbursts, with some of the recent detections departing from the commonly expected behaviors. We thus give an update to the current state of iron band absorption lines detections, through the analysis of all publicly available XMM-$Newton$-PN and $Chandra$-HETG exposures of known Black Hole Low-Mass X-ray Binary candidates. Our results agree with previous studies, with wind detections exclusively found in dipping, high-inclined sources, and almost exclusively in bright ($L_{X}>0.01L_{Edd}$) soft ($HR<0.8$) states, with blueshift values generally restricted to few 100 km s$^{-1}$. The line parameters indicate similar properties between objects and outbursts of single sources, and despite more than 20 years of data, very few sources have the HID sampling necessary to properly study the evolution of the wind during single outbursts. We provide an online tool with details of the wind signatures and outburst evolution data for all sources in the sample.

Authors:Xin-Ying Song

Abstract: The recent extremely bright GRB 230307A from a binary neutron star merger may offer a good probe for the production of GRB-neutrinos. Within the constraint from IceCube neutrino non-detection, the limitations for key physical parameters of this burst are extracted in different scenarios including the fireball, Poynting-flux-dominated (PFD) and hybrid jet. Different from the former nearby `monsters' and due to its smaller isotropic equivalent radiated energy ($E_{\gamma,\rm iso}\sim4\times10^{52}$ erg), the constraint seems loose if non-thermal neutrinos produced from photomeson interactions are the only consideration. However, a quasi-thermal neutrino emission from hadronuclear processes is constrained in this neutron-rich post-merger environment, and the upper limit of the allowed nucleon loading factor is about a few. Based on this, a discussion is presented on the possible prompt emission mechanism and jet composition for GRB 230307A in the context of multi-messenger astrophysics.

Authors:A. I. Bogomazov, A. V. Tutukov

Abstract: In this population synthesis work we study a variety of possible origin channels of supernovae type Ia (SNe Ia) Among them mergers of carbon-oxygen (CO) and oxygen-neon (ONe) white dwarfs (WDs) under the influence of gravitational waves are considered as the primary channel of SNe Ia formation. We estimated frequencies of mergers of WDs with different chemical compositions and distributions of masses of merging WDs. We computed the dependence of the ratio of merger frequencies of ONe and CO WDs as primaries in corresponding binaries on time. The scatter of masses of considered sources (up to the factor $1.5-2$) of SNe Ia is important and should be carefully studied with other sophisticated methods from theoretical point of view. Our ``game of parameters'' potentially explains the increased dimming of SNe Ia in the redshift range $z\approx 0.5-1$ by the changes in the ratio of ONe and CO WDs, i.e., to describe the observed accelerated expansion of the Universe in terms of the evolution of properties of SNe Ia instead of cosmological explanations. This example shows the extreme importance of theoretical studies of problems concerning SNe Ia, because evolutionary scenario and parameter games in nature potentially lead to confusions in their empirical standardization and, therefore, they can influence on cosmological conclusions.

Authors:A. Marino, T. D. Russell, M. Del Santo, A. Beri, A. Sanna, F. Coti Zelati, N. Degenaar, D. Altamirano, E. Ambrosi, A. Anitra, F. Carotenuto, A. D'Ai, T. Di Salvo, A. Manca, S. E. Motta, C. Pinto, F. Pintore, N. Rea, J. Van den Eijnden

Abstract: The accretion flow / jet correlation in neutron star (NS) low-mass X-ray binaries (LMXBs) is far less understood when compared to black hole (BH) LMXBs. In this paper we will present the results of a dense multi-wavelength observational campaign on the NS LMXB 4U 1820-30, including X-ray (Nicer, NuSTAR and AstroSAT) and quasi-simultaneous radio (ATCA) observations in 2022. 4U 1820-30 shows a peculiar 170 day super-orbital accretion modulation, during which the system evolves between "modes" of high and low X-ray flux. During our monitoring, the source did not show any transition to a full hard state. X-ray spectra were well described using a disc blackbody, a Comptonisation spectrum along with a Fe K emission line at 6.6 keV. Our results show that the observed X-ray flux modulation is almost entirely produced by changes in the size of the region providing seed photons for the Comptonisation spectrum. This region is large (about 15 km) in the high mode and likely coincides with the whole boundary layer, while it shrinks significantly (<10 km) in low mode. The electron temperature of the corona and the observed RMS variability in the hard X-rays also exhibit a slight increase in low mode. As the source moves from high to low mode, the radio emission due to the jet becomes about 5 fainter. These radio changes appear not to be strongly connected to the hard-to-soft transitions as in BH systems, while they seem to be connected mostly to variations observed in the boundary layer.

Authors:Vivek Kumar Jha, Ravi Joshi, Jayesh Saraswat, Hum Chand, Sudhanshu Barway, Amit Kumar Mandal

Abstract: In the innermost regions of Active Galactic Nuclei (AGN), matter is understood to be flowing onto the Supermassive black hole (SMBH), which forms an accretion disk. This disk is responsible for the optical/UV continuum emission observed in the spectra of AGN. Reverberation Mapping of the accretion disk using multiple bands can yield the structure of the disk. The emission is expected to be of the black body type peaking at different wavelengths. Hence, depending on the temperature of the disk, continuous, simultaneous monitoring in multiple wavelength ranges to cover hotter inner regions and cooler outer regions can yield the structure and temperature profile of the accretion disk itself. In this study, we present initial results from our accretion disk reverberation mapping campaign targeting AGN with Super High Eddington Accreting Black Holes (SEAMBH). Our analysis on one of the sources- IRAS 04416+1215; based on the broadband observations using the Growth India telescope (GIT), reveals that the size of the accretion disk for this source, calculated by cross-correlating the continuum light curves is larger than expected from the theoretical model. We fit the light curves directly using the thin disk model available in {\sc javelin} and find that the disk sizes are approximately 4 times larger than expected from the Shakura Sunyaev (SS) disk model. Further studies are needed to understand better the structure and physics of AGN accretion disks and their role in the evolution of galaxies.

Authors:Rahul Sharma, Chetana Jain, Biswajit Paul

Abstract: We present a comprehensive analysis of X-ray pulsar 4U 1626-67 during its current spin-down (2SD) state, following a recent torque reversal. Since its discovery, this ultra-compact binary has experienced multiple torque states, transitioning from spin-up (1SU) during 1977-1990 to spin-down (1SD) during 1990-2008, and again spin-up (2SU) until 2023. From NuSTAR observation of May 2023, we have investigated the timing and spectral properties of this pulsar during its 2SD phase, while also comparing them with previous spin-up-down states. For energies upto 8 keV, a distinct bi-horned pulse profile was observed during the spin-up phase, while several sub-structures emerged during spin-down. Beyond 8 keV, a broad asymmetric peak was consistently observed across all torque states. The pulse fraction during the 2SD phase was higher than that during 2SU phase. A prominent ~46.8 mHz quasi-periodic oscillation has been exclusively detected during the spin-down phase. The broadband spectrum during the 2SD phase is described by empirical NPEX model, cyclotron absorption feature and its first harmonic. The spectrum during 2SU phase requires an additional blackbody component and asymmetry in the cyclotron absorption line. A significant flux drop by a factor of ~3 in the 2SD was observed.

Authors:Ning Jiang, Ziying Zhou, Jiazheng Zhu, Yibo Wang, Tinggui Wang

Abstract: Recently, three optical tidal disruption event (TDE) candidates discovered by the Zwicky Transient Facility (ZTF) have been suggested to be coincident with high-energy neutrinos. They all exhibit unusually strong dust infrared (IR) echoes, with their peak times matching the neutrino arrival time even better than the optical peaks. We hereby report on two new TDE candidates that are spatially and temporally coincident with neutrinos by matching our sample of mid-infrared outbursts in nearby galaxies (MIRONG) with Gold alerts of IceCube high-energy neutrino events up to June 2022. The two candidates show negligible optical variability according to their ZTF light curves and can therefore be classified as part of the growing population of obscured TDE candidates. The chance probability of finding two such candidates about $\sim3\%$ by redistributing the MIRONG sources randomly in the SDSS footprint, which will be as low as $\sim0.1\%$ (or $\sim0.2\%$) if we limit to sources with increased fluxes (or variability amplitudes) comparable with the matched two sources. Our findings further support the potential connection between high-energy neutrinos and TDEs in dusty environments by increasing the total number of neutrino-associated TDE and TDE candidates to five, although the underlying physics remains poorly understood.

Authors:Ayshea Bains, Trent English, Nickolas Solomey

Abstract: This research is to determine at Earth the high-energy neutrino flux coming from the galactic core, and from the many other accretion disks within the galactic core. It is estimated there are 10,000 such accretion disk within the cubic parsec of the galactic core alone and many more in the galactic core halo. There are various neutrino detectors, such as IceCube, which can detect energetic neutrinos. However, the direct galactic core neutrino flux is exceptionally low, so very few neutrinos from the galactic core are measured. We created two models to simulate the galactic core neutrino flux. To better estimate the neutrino flux we randomly distributed the accretion disks and generated bodies of varying sizes. This was then used to determine the ultra-high energy neutrino flux. Since it is extremely difficult to determine neutrino direction from interactions of neutrinos, we envision an application where the energetic galactic core neutrinos are gravitationally focused by the Sun with a large light collecting power of eleven to twelve orders of magnitude. They could interact in a planet's atmosphere where the produced showers containing energetic charged particles can produce Cherenkov rings imageable by an orbiting spacecraft or upward going muons which can be observed in a cosmic ray experiment. Estimating the flux will provide a general approximation of the number of ultra-high energy neutrinos that should reach Earth, with Earth being the overall detector. Moreover, studying the neutrinos will provide more information on the conditions of the galactic region, and allow characterizations of it to be formed.

Authors:Abhishek Desai for the IceCube Collaboration, Jessie Thwaites for the IceCube Collaboration, Justin Vandenbroucke for the IceCube Collaboration

Abstract: Astrophysical neutrinos detected by the IceCube observatory can be of Galactic or extragalactic origin. The collective contribution of all the detected neutrinos allows us to measure the total diffuse neutrino Galactic and extragalactic signal. In this work, we describe a simulation package that makes use of this diffuse Galactic contribution information to simulate a population of Galactic sources distributed in a manner similar to our own galaxy. This is then compared with the sensitivities reported by different IceCube data samples to estimate the number of sources that IceCube can detect. We provide the results of the simulation that allows us to make statements about the nature of the sources contributing to the IceCube diffuse signal.

Authors:Jessie Thwaites for the IceCube Collaboration, Aswathi Balagopal V. for the IceCube Collaboration, Sam Hori for the IceCube Collaboration, M. J. Romfoe for the IceCube Collaboration, Albert Zhang for the IceCube Collaboration

Abstract: Searches for neutrinos from gravitational wave events have been performed utilizing the wide energy range of the IceCube Neutrino Observatory. We discuss results from these searches during the third observing run (O3) of the advanced LIGO and Virgo detectors, including a low-latency follow-up of public candidate alert events in O3, an archival search on high-energy track data, and a low-energy search employing IceCube-DeepCore. The dataset of high-energy tracks is mainly sensitive to muon neutrinos, while the low energy dataset is sensitive to neutrinos of all flavors. In all of these searches, we present upper limits on the neutrino flux and isotropic equivalent energy emitted in neutrinos. We also discuss future plans for additional searches, including extending the low-latency follow-up to the next observing run of the LIGO-Virgo-KAGRA detectors (O4) and analysis of gravitational wave (GW) events using a high-energy cascade dataset, which are produced by electron neutrino charged-current interactions and neutral-current interactions from neutrinos of all flavors.

Authors:Divya Rawat IUCAA, Akash Garg IUCAA, Mariano Méndez Kapteyn Astronomical Institute

Abstract: We probe the spectropolarimetric properties of the black-hole binary source 4U 1630$-$47 in the steep power law state. We detect a significant polarization fraction of $\sim$7 % at a polarization angle of $\sim$21 $^\circ$. The $2-12$ keV NICER spectrum can be fitted with a combination of a thermal and a Comptonization component, the latter characterized by a spectral index, $\Gamma \sim$2.1, along with a reflection feature at $\sim$7.0 keV. In the $2-8$ keV band, the degree of polarization of 4U 1630$-$47 in the steep power law state is 4.4 $\sigma$ different from the value previously measured in the high soft state. In the steep power law state, the polarization fraction increases as a function of energy but exhibits an overall drop in each energy band compared to that of the high soft state. We propose that the decrease in the polarization fraction in the steep power law state could be attributed to the presence of a corona. The observed polarization properties in both states can be explained by the self-irradiation of the disk around a Kerr black hole, likely influenced by the frame-dragging effect.

Authors:Sreetama Goswami for the IceCube Collaboration

Abstract: Active Galactic Nuclei (AGN) are powerful astronomical objects with very high luminosities. Theoretical arguments suggest that these objects are capable of accelerating particles to energies of 10$^{20}$ eV. In environments with matter or photon targets, cosmic-ray interactions transpire leading to the production of pionic gamma rays and neutrinos. Since the AGN environment is rich in gas, dust and photons, they are promising candidate sources of high-energy astrophysical neutrinos. While the neutrinos manage to escape, the gamma rays may further interact and cascade down to hard X-rays in environments with sufficiently large photon or gas targets. We have used 12 years of IceCube data to perform a stacked search and a point source search for high-energy neutrino emission from hard X-ray AGN sampled from $\textit{Swift}$-BAT Spectroscopic Survey (BASS) and present the results of these two analyses.

Authors:Jessie Thwaites for the IceCube Collaboration, Justin Vandenbroucke for the IceCube Collaboration

Abstract: Despite being one of the longest known classes of astrophysical transients, novae continue to present modern surprises. The Fermi-LAT discovered that many if not all novae are GeV gamma ray sources, even though theoretical models had not even considered them as a possible source class. More recently, MAGIC and H.E.S.S. detected TeV gamma rays from a nova. Moreover, there is strong evidence that the gamma rays are produced hadronically, and that the long-studied optical emission by novae is also shock-powered. If this is true, novae should emit a neutrino signal correlated with their gamma-ray and optical signals. We present the first search for neutrinos from novae. Because the neutrino energy spectrum is expected to match the gamma-ray spectrum, we use an IceCube DeepCore event selection focused on GeV-TeV neutrinos. We present results from two searches, one for neutrinos correlated with gamma-ray emission and one for neutrinos correlated with optical emission. The event selection presented here is promising for additional astrophysical transients including gamma-ray bursts and gravitational wave sources.

Authors:Ava Ghadimi for the IceCube Collaboration, Marcos Santander for the IceCube Collaboration

Abstract: Neutron stars with very strong magnetic fields are known as magnetars. There are multiple theories that predict magnetars may be able to emit high-energy (HE) neutrinos through hadronic processes by accelerating cosmic rays to high energies. A subclass of magnetars known as soft gamma-ray repeaters (SGRs) can produce giant flares that can result in the production of HE neutrinos. Some magnetars also exhibit bursting activity during which they may emit HE neutrinos. Here we describe our time-integrated search for neutrino emission from magnetars listed in the McGill Online Magnetar Catalog and three newly discovered magnetars SGR 1830-0645, Swift J1555.5-5402, and NGC 253. SGR 1830-0645 and Swift J1555.2-5402 were discovered in 2020 and 2021 respectively by SWIFT after emitting short bursts. A very bright short gamma-ray burst that is believed to be a magnetar giant flare has been localized to NGC 253. We use 14 years of well-reconstructed muon-neutrino candidate events collected by the IceCube Neutrino Observatory to look for significant clustering in the direction of magnetars.

Authors:Martina Karl for the IceCube Collaboration

Abstract: We search for additional neutrino emission from the direction of IceCube's highest energy public alert events. We take the arrival direction of 122 events with a high probability of being of astrophysical origin and look for steady and transient emission. We investigate 11 years of reprocessed and recalibrated archival IceCube data. For the steady scenario, we investigate if the potential emission is dominated by a single strong source or by many weaker sources. In contrast, for the transient emission we only search for single sources. In both cases, we find no significant additional neutrino component. Not having observed any significant excess, we constrain the maximal neutrino flux coming from all 122 origin directions (including the high-energy events) to $\Phi_{90\%,~100~\rm{TeV}} = 1.2 \times 10^{-15}$~(TeV cm$^2$ s)$^{-1}$ at 100~TeV, assuming an $E^{-2}$ emission, with 90\% confidence. The most significant transient emission of all 122 investigated regions of interest is the neutrino flare associated with the blazar TXS~0506+056. With the recalibrated data, the flare properties of this work agree with previous results. We fit a Gaussian time profile centered at $\mu_T = 57001 ^{+38}_{-26}$~MJD and with a width of $\sigma_T = 64 ^{+35}_{-10}$~days. The best fit spectral index is $\gamma = 2.3 \pm 0.4$ and we fit a single flavor fluence of $J_{100~\rm{TeV}} = 1.2 ^{+1.1} _{-0.8} \times 10^{-8} $~(TeV~cm$^2$)$^{-1}$. The global p-value for transient emission is $p_{\rm{global}} = 0.156$ and, therefore, compatible with background.

Authors:Roxanne Turcotte for the IceCube Collaboration, Stef Verpoest for the IceCube Collaboration, Megha Venugopal for the IceCube Collaboration

Abstract: The IceCube Neutrino Observatory at the geographic South Pole is, with its surface and in-ice detectors, used for both neutrino and cosmic-ray physics. The surface array, named IceTop, consists of ice-Cherenkov tanks grouped in 81 pairs spanning a 1 km$^2$ area. An enhancement of the surface array, composed of elevated scintillation panels and radio antennas, was designed over the last years in order to increase the scientific capabilities of IceTop. The surface radio antennas, in particular, will be able to reconstruct $X_\mathrm{max}$, an observable widely used to determine the mass composition of cosmic rays. A complete prototype station of this enhanced array was deployed in the Austral summer of 2019/20 at the South Pole. This station comprises three antennas and eight scintillation panels, arranged in a three-arms star shape. The nominal frequency band of the radio antennas is 70 to 350 MHz. In this work, we use a state-of-the-art reconstruction method in which observed events are compared directly to CoREAS simulations to obtain an estimation of the air-shower variables, in particular, energy and $X_\mathrm{max}$. We will show the results in this unique frequency band using the three prototype antennas.

Authors:Sandeep K. Rout PRL, Mariano Mendez Kapteyn, Federico Garcia UNLP

Abstract: The study of quasi periodic oscillations (QPOs) plays a vital role in understanding the nature and geometry of the Comptonizing medium around black-hole X-ray binaries. The spectral-state dependence of various types of QPOs (namely A, B, & C) suggests that they could have different origins. The simultaneous presence of different types of QPOs would therefore imply the simultaneous occurrence of different mechanisms. In this work we study the radiative properties of two non-harmonically related QPOs in the black-hole binary GRO J1655--40 detected at the peak of the ultraluminous state during the 2005 outburst of the source. The two QPOs have been previously identified as types B & C, respectively. We jointly fit the phase-lag and rms spectra of the QPOs and the time-averaged spectrum of the source with the time-dependent Comptonization model vkompth to infer the geometry of the media producing the QPOs. The time-averaged spectrum required a hot disk of 2.3 keV and a steep power law with index 2.7, revealing that the source was in an ultraluminous state. The corona that drives the variability of the type-B QPO is smaller in size and has a lower feedback fraction than the one that drives the variability of the type-C QPO. This suggests the simultaneous presence of a horizontally extended corona covering the accretion disk and a vertically elongated jet-like corona that are responsible for the type-B & C QPOs, respectively.

Authors:Caterina Boscolo Meneguolo for the IceCube Collaboration, Elisa Bernardini for the IceCube Collaboration, Sarah Mancina for the IceCube Collaboration

Abstract: The IceCube Neutrino Observatory has the invaluable capability of continuously monitoring the whole sky. This has affirmed the role of IceCube as a sentinel, providing real-time alerts to the astrophysical community on the detection of high-energy neutrinos and neutrino flares from a variety of astrophysical sources. As a response to the IceCube alerts, different observatories can join forces in the multi-messenger observation of transient events and the characterisation of their astrophysical sources. The 2017 breakthrough identification of blazar TXS 0506+056 as the source of high-energy neutrinos and UHE gamma rays was proof of this strategy. The Gamma-ray Follow-Up (GFU) is the IceCube program for identifying high-energy muon neutrino single events, as well as outstanding neutrino flares from relevant sources and the whole wide universe. While the identification of single high-energy neutrinos is shared on public alert distribution networks, partner Imaging Air Cherenkov Telescopes are sent low-latency alerts following the detection of neutrino flares, for which they have dedicated follow-up programs. I will present an overview of the GFU platform together with new results from the analysis of recorded neutrino flares, after a dozen years of GFU operation and hundreds of alerts being sent.

Authors:Carlos Hugo López-Caraballo, Beatriz Ruiz-Granados, Ricardo Genova Santos, Mateo Fernández-Torreiro, Jose Alberto Rubiño-Martin, Mike Peel, Frederick Poidevin, Eduardo Artal, Mark Ashdown, Rita Belen Barreiro, Francisco Javier Casas, Elena de la Hoz, Raul González-González, Federica Guidi, Diego Herranz, Roger Hoyland, Anthony N Lasenby, Enrique Martinez-Gonzalez, Lucio Piccirillo, Rafael Rebolo, Denis Tramonte, Flavien Vansyngel, Patricio Vielva, Robert Watson

Abstract: We use the new QUIJOTE-MFI wide survey (11, 13, 17 and 19 GHz) to produce spectral energy distributions (SEDs), on an angular scale of 1 deg, of the supernova remnants (SNRs) CTB 80, Cygnus Loop, HB 21, CTA 1, Tycho and HB 9. We provide new measurements of the polarized synchrotron radiation in the microwave range. For each SNR, the intensity and polarization SEDs are obtained and modelled by combining QUIJOTE-MFI maps with ancillary data. In intensity, we confirm the curved power law spectra of CTB 80 and HB 21 with a break frequency $\nu_{\rm b}$ at 2.0$^{+1.2}_{-0.5}$ GHz and 5.0$^{+1.2}_{-1.0}$ GHz respectively; and spectral indices respectively below and above the spectral break of $-0.34\pm0.04$ and $-0.86\pm0.5$ for CTB 80, and $-0.24\pm0.07$ and $-0.60\pm0.05$ for HB 21. In addition, we provide upper limits on the Anomalous Microwave Emission (AME), suggesting that the AME contribution is negligible towards these remnants. From a simultaneous intensity and polarization fit, we recover synchrotron spectral indices as flat as $-0.24$, and the whole sample has a mean and scatter of $-0.44\pm0.12$. The polarization fractions have a mean and scatter of $6.1\pm1.9$\%. When combining our results with the measurements from other QUIJOTE studies of SNRs, we find that radio spectral indices are flatter for mature SNRs, and particularly flatter for CTB 80 ($-0.24^{+0.07}_{-0.06}$) and HB 21 ($-0.34^{+0.04}_{-0.03}$). In addition, the evolution of the spectral indices against the SNRs age is modelled with a power-law function, providing an exponent $-0.07\pm0.03$ and amplitude $-0.49\pm0.02$ (normalised at 10 kyr), which are conservative with respect to previous studies of our Galaxy and the Large Magellanic Cloud.

Authors:Jannis Necker for the IceCube Collaboration

Abstract: The collected data of IceCube, a cubic kilometre neutrino detector array in the Antarctic ice, reveal a diffuse flux of astrophysical neutrinos. The extragalactic sources of the majority of these neutrinos however have yet to be discovered. Tidal Disruption Events (TDEs), disruption outbursts from black holes that accrete at an enhanced rate, are candidates for being the sources of extragalactic, high-energy neutrinos. Stein et al. (2021) and Reusch et al. (2022) have reported the coincidence of two likely TDEs from supermassive black holes and public IceCube neutrino events (alerts). Further work by van Velzen et al. (2021) identified a third event in coincidence with a high-energy neutrino alert and a $3.7 \sigma$ correlation between a broader set of similar TDE-like flares and IceCube alerts. We conducted a stacking analysis with a 29-flare subset of the TDE-like flares tested by van Velzen et al. This work was done with neutrinos with energies above $\mathcal{O}(100)$ GeV. The resulting p-value of 0.45 is consistent with background. In this contribution, I will discuss the results of the stacking analysis, as well as the impact of using different reconstruction algorithms on the three correlated realtime alerts.

Authors:Rahul Gupta, S. B. Pandey, Amit K. Ror, Amar Aryan, S. N. Tiwari

Abstract: India has been actively involved in the follow-up observations of optical afterglows of gamma-ray bursts (GRBs) for more than two decades, using the country's meter-class facilities such as the 1.04 m Sampurnanand Telescope, 1.3 m Devasthal Fast Optical Telescope, 2.01 m Himalayan Chandra Telescope along with many others in the country, utilizing the longitudinal advantage of the place. However, since 2016, Indian astronomers have embarked on a new era of exploration by utilizing the country's largest optical telescope, the 3.6 m Devasthal Optical Telescope (DOT) at the Devasthal Observatory of ARIES Nainital. This unique telescope has opened up exciting opportunities for transient study. Starting from the installation itself, the DOT has been actively performing the target of opportunity (ToO) observations, leading to many interesting discoveries. Notable achievements include the contributions towards the discovery of long GRB 211211A arising from a binary merger, the discovery of the most delayed optical flare from GRB 210204A along with the very faint optical afterglow (fainter than 25 mag in g-band) of GRB 200412B. We also successfully observed the optical counterpart of the very-high-energy (VHE) detected burst GRB 201015A using DOT. Additionally, DOT has been used for follow-up observations of dark and orphan afterglows, along with the observations of host galaxies associated with peculiar GRBs. More recently, DOT's near-IR follow-up capabilities helped us to detect the first near-IR counterpart (GRB 230409B) using an Indian telescope. In this work, we summarise the recent discoveries and observations of GRBs using the 3.6 m DOT, highlighting the significant contributions in revealing the mysteries of these cosmic transients.

Authors:McKinley C. Brumback, Georgios Vasilopolous, Joel B. Coley, Kristen Dage, Jon M. Miller

Abstract: Neutron star high mass X-ray binaries with superorbital modulations in luminosity host warped inner accretion disks that occult the neutron star during precession. In SMC X-1, the instability in the warped disk geometry causes superorbital period "excursions:" times of instability when the superorbital period decreases from its typical value of 55 days to $\sim$40 days. Disk instability makes SMC X-1 an ideal system in which to investigate the effects of variable disk geometry on the inner accretion flow. Using the high resolution spectral and timing capabilities of the Neutron Star Interior Composition Explorer (NICER) we examined the high state of four different superorbital cycles of SMC X-1 to search forchanges in spectral shape and connections to the unstable disk geometry. We performed pulse phase-averaged and phase-resolved spectroscopy to closely compare the changes in spectral shape and any cycle-to-cycle variations. While some parameters including the photon index and absorbing column density show slight variations with superorbital phase, these changes are most evident during the intermediate state of the supeorbital cycle. Few spectral changes are observed within the high state of the superorbital cycle, possibly indicating the disk instability does not significantly change SMC X-1's accretion process.

Authors:Shiqi Yu for the IceCube Collaboration, Ali Kheirandish for the IceCube Collaboration, Qinrui Liu for the IceCube Collaboration, Hans Niederhausen for the IceCube Collaboration

Abstract: Supermassive black holes (SMBHs) power active galactic nuclei (AGN). The vicinity of the SMBH has long been proposed as the potential site of particle acceleration and neutrino production. Recently, IceCube reported evidence of neutrino emission from the Seyfert II galaxy NGC 1068. The absence of a matching flux of TeV gamma rays suggests that neutrinos are produced where gamma rays can efficiently get attenuated, for example, in the hot coronal environment near the SMBH at the core of the AGN. Here, we select the intrinsically brightest (in X-ray) Seyfert galaxies in the Southern Sky from the BAT AGN Spectroscopic Survey (BASS) and search for associated neutrinos using starting track events in IceCube. In addition to the standard power law flux assumption, we leverage a dedicated disc-corona model of neutrino production in such an environment to improve the discovery potential of the search. In this contribution, we report on the expected performance of our searches for neutrinos from these Seyfert galaxies.

Authors:Leonardo Supán, Gabriela Castelletti, Anne Lemière

Abstract: This paper presents a comprehensive analysis of the Galactic SNR Kes 17 (G304.6+0.1) with focus on its radio synchrotron emission, environs, and the factors contributing to the observed gamma rays. The firstly-obtained integrated radio continuum spectrum from 88 to 8800 MHz yields an index alpha = -0.488 +/- 0.023 (S_nu $\propto$ nu^alpha), indicative of a linear particle acceleration process at the shock front. Accounting for the SNR radio shell size, the distribution of atomic hydrogen (n_H ~ 10 cm^-3), and assuming the SNR is in the Sedov-Taylor stage of its evolution, we estimate Kes 17 to be roughly 11 kyr. From 12CO and 13CO (J=1-0) emission-line data as a proxy for molecular hydrogen we provided the first evidence that the eastern shell of Kes 17 is engulfing a molecular enhancement, with 4.2 x 10^4 M_sun and n ~ 300 cm^-3. Towards the western boundary of Kes 17 there are not CO signatures above 3 sigma, despite previously reported infrared observations have revealed shocked molecular gas at that location. This suggests the existence of a CO-dark interacting molecular gas, a phenomenon also recorded in other Galactic SNRs (e.g. CTB 37A and RX J1713.7-3946). Additionally, by analysing ~14.5 yr of data from Fermi-LAT, we determined a power-law photon index in the 0.3-300 GeV range of Gamma = 2.39 +/- 0.04^+0.063_-0.114 (+/-stat +/-syst) in agreement with prior studies. The energy flux turns out to be (2.98 +/- 0.14) x 10^-11 erg cm-2 s-1 implying a luminosity (2.22 +/- 0.45) x 10^35 erg s-1 at ~8 kpc. Finally, we successfully modelled the multiwavelength SED by incorporating the improved radio synchrotron spectrum and the new gamma-ray measurements. Our analysis indicates that the observed GeV flux most likely originates from the interaction of Kes 17 with western ''dark'' CO zone with a proton density n_p ~ 400 cm-3.

Authors:Noam Soker Technion, Israel

Abstract: Under the assumption that jets explode all core collapse supernovae (CCSNe) I classify 13 CCSN remnants (CCSNRs) into five groups according to their morphology as shaped by jets, and attribute the classes to the specific angular momentum of the pre-collapse core. Point-symmetry (1 CCSNR): According to the jittering jets explosion mechanism (JJEM) when the pre-collapse core rotates very slowly the newly born neutron star (NS) launches tens of jet-pairs in all directions. The last several jet-pairs might leave an imprint of several pairs of ears, i.e., a point-symmetric morphology. One pair of ears (7 CCSNRs): More rapidly rotating cores might force the last pair of jets to be long-lived and shape one pair of jet-inflated ears that dominate the morphology. S-shaped (1 CCSNR): The accretion disk might precess, leading to an S-shaped morphology. Barrel-shaped (3 CCSNRs): Even more rapidly rotating pre-collapse cores might result in a final energetic pair of jets that clear the region along the axis of the pre-collapse core rotation and form a barrel-shaped morphology. Elongated (1 CCSNR): Very rapidly rotating pre-collapse core force all jets to be along the same axis such that the jets are inefficient in expelling mass from the equatorial plane and the long-lasting accretion process turns the NS into a black hole (BH). The two new results of this study are the classification of CCSNRs into five classes based on jet-shaped morphological features, and the attribution of the morphological classes mainly to the pre-collapse core rotation in the frame of the JJEM.

Authors:Sovan Chakraborty, Poonam Mehta, Prantik Sarmah

Abstract: Ultra-high energy cosmic rays (UHECRs) beyond the Greisen-Zatsepin-Kuzmin (GZK) cut-off provide us with a unique opportunity to understand the universe at extreme energies. Secondary GZK photons and GZK neutrinos associated with the same interaction are indeed interconnected and render access to multi-messenger analysis of UHECRs. The GZK photon flux is heavily attenuated due to the interaction with Cosmic Microwave Background (CMB) and the Extra-galactic Radio Background (ERB). The present estimate of the ERB comprising of several model uncertainties together with the ARCADE2 radio excess results in large propagation uncertainties in the GZK photon flux. On the other hand, the weakly interacting GZK neutrino flux is unaffected by these propagation effects. In this work, we make an updated estimate of the GZK photon and GZK neutrino fluxes considering a wide variation of both the production and propagation properties of the UHECR like, the spectral index, the cut-off energy of the primary spectrum, the distribution of sources and the uncertainties in the ERB estimation. We explore the detection prospects of the GZK fluxes with various present and upcoming UHECR and UHE neutrino detectors such as Auger, TA, GRAND, ANITA, ARA, IceCube and IceCube-Gen2. The predicted fluxes are found to be beyond the reach of the current detectors. In future, proposed IceCube-Gen2, AUGER upgrade and GRAND experiments will have the sensitivity to the predicted GZK photon and GZK neutrino fluxes. Such detection can put constraints on the UHECR source properties and the propagation effects due to the ERB. We also propose an indirect lower limit on the GZK photon flux using the neutrino-photon connection for any future detection of GZK neutrinos by the IceCube-Gen2 detector. We find this limit to be consistent with our GZK flux predictions.

Authors:Wenjie Hou for the IceCube-Gen2 Collaboration

Abstract: The energy of the transition from Galactic to extra-galactic origin of cosmic rays is one of the major unresolved issues of cosmic-ray physics. However, strong constraints can be obtained from studying the anisotropy in the arrival directions of cosmic rays. The sensitivity to cosmic-ray anisotropy is, in particular, a matter of statistics. Recently, the cosmic ray anisotropy measurements in the TeV to PeV energy range were updated from IceCube using 11 years of data. The IceCube-Gen2 surface array will cover an area about 8 times larger than the existing IceTop surface array with a corresponding increase in statistics and capability to investigate cosmic-ray anisotropy with higher sensitivity. In this contribution, we present details on the performed simulation studies and sensitivity to the cosmic-ray anisotropy signal for the IceCube-Gen2 surface array.

Authors:Stef Verpoest for the IceCube Collaboration

Abstract: We report on an analysis of the high-energy muon component in near-vertical extensive air showers detected by the surface array IceTop in coincidence with the in-ice array of the IceCube Neutrino Observatory. In the coincidence measurement, the predominantly electromagnetic signal measured by IceTop is used to estimate the cosmic-ray primary energy, and the energy loss of the muon bundle in the deep in-ice array is used to estimate the number of muons in the shower with energies above 500 GeV ("TeV muons"). The average multiplicity of these TeV muons is determined for cosmic-ray energies between 2.5 PeV and 100 PeV assuming three different hadronic interaction models: Sibyll 2.1, QGSJet-II.04, and EPOS-LHC. For all models considered, the results are found to be in good agreement with the expectations from simulations. A tension exists, however, between the high-energy muon multiplicity and other observables; most importantly the density of GeV muons measured by IceTop using QGSJet-II.04 and EPOS-LHC.

Authors:Lachlan Marnoch Macquarie University CSIRO Space and Astronomy Astrophysics and Space Technologies Research Centre ASTRO 3D, Stuart D. Ryder Macquarie University Astrophysics and Space Technologies Research Centre, Clancy W. James International Centre for Radio Astronomy Research, Alexa C. Gordon Northwestern University, Mawson W. Sammons International Centre for Radio Astronomy Research, J. Xavier Prochaska University of California Kavli Institute for the Physics and Mathematics of the Universe National Astronomical Observatory of Japan, Nicolas Tejos Pontificia Universidad Católica de Valparaíso, Adam T. Deller Swinburne University of Technology, Danica R. Scott International Centre for Radio Astronomy Research, Shivani Bhandari CSIRO Space and Astronomy Netherlands Institute for Radio Astronomy Joint institute for VLBI ERIC Anton Pannekoek Institute for Astronomy, Marcin Glowacki International Centre for Radio Astronomy Research, Elizabeth K. Mahony CSIRO Space and Astronomy, Richard M. McDermid Macquarie University Astrophysics and Space Technologies Research Centre ASTRO 3D, Elaine M. Sadler Sydney Institute for Astronomy CSIRO Space and Astronomy ASTRO 3D, Ryan M. Shannon Swinburne University of Technology, Hao Qiu SKA Observatory

Abstract: FRB 20210912A is a fast radio burst (FRB), detected and localised to sub-arcsecond precision by the Australian Square Kilometre Array Pathfinder. No host galaxy has been identified for this burst despite the high precision of its localisation and deep optical and infrared follow-up, to 5-$\sigma$ limits of $R=26.7$ mag and $K_\mathrm{s}=24.9$ mag with the Very Large Telescope. The combination of precise radio localisation and deep optical imaging has almost always resulted in the secure identification of a host galaxy, and this is the first case in which the line-of-sight is not obscured by the Galactic disk. The dispersion measure of this burst, $\mathrm{DM_{FRB}}=1233.696\pm0.006~\mathrm{pc}\ \mathrm{cm}^{-3}$, allows for a large source redshift of $z>1$ according to the Macquart relation. It could thus be that the host galaxy is consistent with the known population of FRB hosts, but is too distant to detect in our observations ($z>0.7$ for a host like that of the first repeating FRB source, FRB 20121102A); that it is more nearby with a significant excess in $\mathrm{DM_{host}}$, and thus dimmer than any known FRB host; or, least likely, that the FRB is truly hostless. We consider each possibility, making use of the population of known FRB hosts to frame each scenario. The fact of the missing host has ramifications for the FRB field: even with high-precision localisation and deep follow-up, some FRB hosts may be difficult to detect, with more distant hosts being the less likely to be found. This has implications for FRB cosmology, in which high-redshift detections are valuable.

Authors:Vyacheslav Ivanovich Dokuchaev

Abstract: We reconstructed dark spots in the images of supermassive black holes SgrA* and M87* provided by the Event Horizon Telescope (EHT) collaboration by using the geometrically thin accretion disk model. In this model, the black hole is highlighted by the hot accretion matter up to the very vicinity of the black hole event horizon. The existence of hot accretion matter in the vicinity of black hole event horizons is predicted by the Blandford-Znajek mechanism, which is confirmed by recent general relativistic MHD simulations in supercomputers. A dark spot in the black hole image in the described model is a gravitationally lensed image of an event horizon globe. The lensed images of event horizons are always projected at the celestial sphere inside the awaited positions of the classical black hole shadows, which are invisible in both cases of M87* and SgrA*. We used the sizes of dark spots in the images of SgrA* and M87* for inferring their spins, 0.65<a<0.9 and a>0.75, accordingly.

Authors:Karolin Hymon for the IceCube Collaboration, Tim Ruhe for the IceCube Collaboration

Abstract: The IceCube Neutrino Observatory measures high energy atmospheric neutrinos with high statistics. These atmospheric neutrinos are produced in cosmic ray interactions in the atmosphere, mainly by the decay of pions and kaons. The rate of the measured neutrinos is affected by seasonal temperature variations in the stratosphere, which are expected to increase with the energy of the particle. In this contribution, seasonal energy spectra are obtained using a novel spectrum unfolding approach, the Dortmund Spectrum Estimation Algorithm (DSEA+), in which the energy distribution from 125 GeV to 10 TeV is estimated from measured quantities with machine learning algorithms. The seasonal spectral difference to the annual average flux will be discussed based on preliminary results from IceCube's atmospheric muon neutrino data.

Authors:Leonora Kardum for the IceCube Collaboration

Abstract: IceCube Neutrino Observatory, the cubic kilometer detector embedded in ice of the geographic South Pole, is capable of detecting particles from several GeV up to PeV energies enabling precise neutrino spectrum measurement. The diffuse neutrino flux can be subdivided into three components: astrophysical, from extraterrestrial sources; conventional, from pion and kaon decays in atmospheric Cosmic Ray cascades; and the yet undetected prompt component from the decay of charmed hadrons. A particular focus of this work is to test the predicted angular dependence of the atmospheric neutrino flux using an unfolding method. Unfolding is a set of methods aimed at determining a value from related quantities in a model-independent way, eliminating the influence of several assumptions made in the process. In this work, we unfold the muon neutrino energy spectrum and employ a novel technique for rebinning the observable space to ensure sufficient event numbers within the low statistic region at the highest energies. We present the unfolded energy and zenith angle spectrum reconstructed from IceCube data and compare the result with model expectations and previous measurements.

Authors:M. I. Belvedersky, S. D. Bykov, M. R. Gilfanov

Abstract: We have classified the point-like X-ray sources detected by the SRG/eROSITA telescope in the deep Lockman Hole survey. The goal was to separate the sources into Galactic and extragalactic objects. In this work have used the results of our previous cross-match of X-ray sources with optical catalogs. To classify SRG/eROSITA sources we have used the flux ratio $F_{x}/F_{o}$ and information about the source optical extent. As a result, of the 6885 X-ray sources in the eROSITA catalog 357 sources have been classified as Galactic and 5929 and as extragalactic. 539 out of 6885 have been treated as hostless, i.e., having no optical counterparts in the optical catalogs under consideration. 60 have remained unclassified due to the insufficient reliability of optical photometry. Precision and recall for the extragalactic sources are 99.9 and 98.9% (respectively) and 91.6 and 99.7% for the Galactic sources. Using this classification, we have constructed the curves of cumulative number counts for the Galactic and extragalactic sources in the Lockman Hole field. The code that accompanies this paper is available at https://github.com/mbelveder/ero-lh-class.git.

Authors:H. Tong

Abstract: Recently another long period radio pulsar GPM J1839$-$10 is reported, similar to GLEAM-X J162759.5$-$523504.3. Previously, the energy budget and rotational evolution of long period radio pulsars had been considered. This time, the death line and pulse width for neutron star and white dwarf pulsars are investigated. The pulse width is included as the second criterion for neutron star and white dwarfs pulsars. It is found that: (1) PSR J0250+5854 and PSR J0901$-$4046 etc should be normal radio pulsars. They have narrow pulse width and they lie near the radio emission death line. (2) The two long period radio pulsars GLEAM-X J162759.5$-$523504.3 and GPM J1839$-$10 is unlikely to be normal radio pulsars. Their possible pulse width is relatively large. And they lie far below the fiducial death line on the $P-\dot{P}$ diagram. (3) GLEAM-X J162759.5$-$523504.3 and GPM J1839$-$10 may be magnetars or white dwarf radio pulsars. At present, there are many parameters and uncertainties in both of these two possibilities.

Authors:Stephen Sclafani for the IceCube collaboration, Mirco Huennefeld for the IceCube collaboration

Abstract: IceCube has discovered a flux of astrophysical neutrinos and presented evidence for the first neutrino sources, a flaring blazar known as TXS 0506+056 and the active galaxy NGC 1068. However, the sources responsible for the majority of the astrophysical neutrino flux remain elusive. In addition to hypothetical sources within our Galaxy, high energy neutrinos are produced when cosmic rays interact at their acceleration sites and during propagation through the interstellar medium. The Galactic plane has therefore long been hypothesized as a neutrino source. In this contribution, new results are presented for searches of neutrino sources utilizing a dataset that builds upon recent advances in deep-learning-based reconstruction methods for neutrino-induced cascades. This work presents the first observation of high-energy neutrinos from the Milky Way Galaxy, rejecting the background-only hypothesis at 4.5$\sigma$. The neutrino signal is consistent with diffuse emission from the Galactic plane, potentially in combination with emission by a population of sources.

Authors:Shuo Xiao, Xiao-Bo Li, Wang-Chen Xue, Shao-Lin Xiong, Shuang-Nan Zhang, Wen-Xi Peng, Ai-Jun Dong, You-Li Tuo, Ce Cai, Xi-Hong Luo, Jiao-Jiao Yang, Yue Wang, Chao Zheng, Yan-Qiu Zhang, Jia-Cong Liu, Wen-Jun Tan, Chen-Wei Wang, Ping Wang, Cheng-Kui Li, Shu-Xu Yi, Shi-Jun Dang, Lun-Hua Shang, Ru-Shuang Zhao, Qing-Bo Ma, Wei Xie, Jian-Chao Feng, Bin Zhang, Zhen Zhang, Ming-Yu Ge, Shi-Jie Zheng, Li-Ming Song, Qi-Jun Zhi

Abstract: The study of quasi-periodic oscillations (QPOs) and power density spectra (PDS) continuum properties can help shed light on the still illusive emission physics of magnetars and as a window into the interiors of neutron stars using asteroseismology. In this work, we employ a Bayesian method to search for the QPOs in the hundreds of X-ray bursts from SGR J1935+2154 observed by {\it Insight}-HXMT, GECAM and Fermi/GBM from July 2014 to January 2022. Although no definitive QPO signal (significance $>3\sigma$) is detected in individual bursts or the averaged periodogram of the bursts grouped by duration, we identify several bursts exhibiting possible QPO at $\sim$ 40 Hz, which is consistent with that reported in the X-ray burst associated with FRB 200428. We investigate the PDS continuum properties and find that the distribution of the PDS slope in the simple power-law model peaks $\sim$ 2.5, which is consistent with other magnetars but higher than 5/3 commonly seen in gamma-ray bursts. Besides, the distribution of the break frequency in the broken power-law model peaks at $\sim$ 60 Hz. Finally, we report that the power-law index of PDS has an anti-correlation and power-law dependence on the burst duration as well as the minimum variation timescale.

Authors:B. O'Connor, E. Gogus, J. Hare, K. Mukai, D. Huppenkothen, J. Brink, D. A. H. Buckley, A. Levan, M. G. Baring, R. Stewart, C. Kouveliotou, P. Woudt, E. Bellm, S. B. Cenko, P. A. Evans, J. Granot, C. Hailey, F. Harrison, D. Hartmann, A. J. van der Horst, L. Kaper, J. A. Kennea, S. B. Potter, P. O. Slane, D. Stern, R. A. M. J. Wijers, G. Younes

Abstract: Here, we present the results of our multi-wavelength campaign aimed at classifying \textit{Swift} J170800$-$402551.8 as part of the \textit{Swift} Deep Galactic Plane Survey (DGPS). We utilized Target of Opportunity (ToO) observations with \textit{Swift}, \textit{NICER}, \textit{XMM-Newton}, \textit{NuSTAR}, and the Southern African Large Telescope (SALT), as well as multi-wavelength archival observations from \textit{Gaia}, VPHAS, and VVV. The source displays a periodicity of 784 s in our \textit{XMM-Newton} observation. The X-ray spectrum (\textit{XMM-Newton} and \textit{NuSTAR}) can be described by thermal bremsstrahlung radiation with a temperature of $kT$\,$\approx$\,$30$ keV. The phase-folded X-ray lightcurve displays a double-peaked, energy-dependent pulse-profile. We used \textit{Chandra} to precisely localize the source, allowing us to identify and study the multi-wavelength counterpart. Spectroscopy with SALT identified a Balmer H$\alpha$ line, and potential HeI lines, from the optical counterpart. The faintness of the counterpart ($r$\,$\approx$\,$21$ AB mag) favors a low-mass donor star. Based on these criteria, we classify \textit{Swift} J170800$-$402551.8 as a candidate intermediate polar cataclysmic variable, where the spin period of the white dwarf is 784 s.

Authors:Larissa Paul for the IceCube Collaboration

Abstract: The IceCube Neutrino Observatory is equipped with the unique possibility to measure cosmic ray induced air showers simultaneously by their particle footprint on the surface with the IceTop detector and by the high-energy muonic shower component at a depth of more than 1.5 km. Since 2019 additionally two Imaging Air Cherenkov Telescopes, called IceAct, measure the electromagnetic component of air showers in the atmosphere above the IceCube detector. This opens the possibility to measure air shower parameters in three independent detectors and allows to improve mass composition studies with the IceCube data. One IceAct camera consists of 61 SiPM pixels in a hexagonal grid. Each pixel has a field of view of 1.5 degree resulting in an approximately 12-degree field of view per camera. A single telescope tube has a diameter of 50 cm, is built robust enough to withstand the harsh Antarctic conditions, and is able to detect cosmic ray particles with energies above approximately 10 TeV. A Graph Neural Network (GNN) is trained to determine the air shower properties from IceAct data. The composition analysis is then performed using Random Forest Regression (RF). Since all three detectors have a different energy threshold, we train several RFs with different inputs, combining the different detectors and taking advantage of the lower energy threshold of the IceAct telescopes. This will result in composition measurements for different detector combinations and enables cross-checks of the results in overlapping energy bands. We present the method, parameters for data selection, and the status of this analysis.

Authors:Lars Heuermann for the IceCube Collaboration

Abstract: IceAct is an array of compact Imaging Air Cherenkov Telescopes at the ice surface as part of the IceCube Neutrino Observatory. The telescopes, featuring a camera of 61 silicon photomultipliers and fresnel-lens-based optics, are optimized to be operated in harsh environmental conditions, such as at the South Pole. Since 2019, the first two telescopes have been operating in a stereoscopic configuration in the center of IceCube's surface detector IceTop. With an energy threshold of about 10 TeV and a wide field-of-view, the IceAct telescopes show promising capabilities of improving current cosmic-ray composition studies: measuring the Cherenkov light emissions in the atmosphere adds new information about the shower development not accessible with the current detectors. First simulations indicate that the added information of a single telescope leads, e.g., to an improved discrimination between flux contributions from different primary particle species in the sensitive energy range. We review the performance and detector operations of the telescopes during the past 3 years (2020-2022) and give an outlook on the future of IceAct.

Authors:Sjoerd Bouma for the IceCube-Gen2 Collaboration, Anna Nelles for the IceCube-Gen2 Collaboration

Abstract: The IceCube-Gen2 facility will extend the energy range of IceCube to ultra-high energies. The key component to detect neutrinos with energies above 10 PeV is a large array of in-ice radio detectors. In previous work, direction reconstruction algorithms using the forward-folding technique have been developed for both shallow ($\lesssim 20$ m) and deep in-ice detectors, and have also been successfully used to reconstruct cosmic rays with ARIANNA. Here, we focus on the reconstruction algorithm for the deep in-ice detector, which was recently introduced in the context of the Radio Neutrino Observatory in Greenland (RNO-G). We discuss the performance-critical aspects of the algorithm, as well as recent and future improvements, and apply it to study the performance of a station of the IceCube-Gen2 in-ice radio array. We obtain the angular resolution, which turns out to be strongly asymmetric, and use this to optimize the configuration of a single station.

Authors:Yash Bhargava TIFR, Mumbai, India, Sudip Bhattacharyya TIFR, Mumbai, India, Jeroen Homan Eureka Scientific Inc, Oakland USA, Mayukh Pahari IIT Hyderabad, Kandi, India

Abstract: Understanding the spectral evolution along the `Z'-shaped track in the hardness-intensity diagram of Z-sources, which are a class of luminous neutron star low-mass X-ray binaries, is crucial to probe accretion processes close to the neutron star. Here, we study the horizontal branch (HB) and the normal branch (NB) of the Z source GX 340+0 using $AstroSat$ data. We find that the HB and the NB appear as two different types of X-ray intensity dips, which can appear in any sequence and with various depths. Our $0.8-25$~keV spectra of dips and the hard apex can be modeled by the emissions from an accretion disk, a Comptonizing corona covering the inner disk, and the neutron star surface. We find, as the source moves onto the HB the corona is replenished and energized by the disk and a reduced amount of disk matter reaches the neutron star surface. We also conclude that quasi-periodic oscillations during HB/NB are strongly associated with the corona, and explain the evolution of strength and hard-lag of this timing feature using the estimated coronal optical depth evolution.

Authors:Pengfu Tian, Ping Zhang, Wei Wang, Pei Wang, Xiaohui Sun, Jifeng Liu, Bing Zhang, Zigao Dai, Feng Yuan, Shuangnan Zhang, Qingzhong Liu, Peng Jiang, Xuefeng Wu, Zheng Zheng, Jiashi Chen, Di Li, Zonghong Zhu, Zhichen Pan, Hengqian Gan, Xiao Chen, Na Sai

Abstract: Powerful relativistic jets are one of the ubiquitous features of accreting black holes in all scales. GRS 1915+105 is a well-known fast-spinning black-hole X-ray binary with a relativistic jet, termed as a ``microquasar'', as indicated by its superluminal motion of radio emission. It exhibits persistent x-ray activity over the last 30 years, with quasi-periodic oscillations of $\sim 1-10$ Hz and 34 and 67 Hz in the x-ray band. These oscillations likely originate in the inner accretion disk, but other origins have been considered. Radio observations found variable light curves with quasi-periodic flares or oscillations with periods of $\sim 20-50$ minutes. Here we report two instances of $\sim$5 Hz transient periodic oscillation features from the source detected in the 1.05-1.45 GHz radio band that occurred in January 2021 and June 2022, respectively. Circular polarization was also observed during the oscillation phase.

Authors:G. Sommani for the IceCube Collaboration, C. Lagunas Gualda for the IceCube Collaboration, H. Niederhausen for the IceCube Collaboration

Abstract: Sources of astrophysical neutrinos can potentially be discovered through the detection of neutrinos in coincidence with electromagnetic counterparts. Real-time alerts generated by IceCube play an important role in this search, acting as triggers for follow-up observations with instruments sensitive to electromagnetic signals in various wavelengths. In previous studies, we investigated the treatment of the systematic uncertainties on the reconstruction method currently used in IceCube's real-time program, concluding that a new approach, more robust against systematic variations, is needed. Here we present the state-of-the-art of these analyses, and discuss a modification to an already-existing and reliable reconstruction method that results in an improved solution under many metrics. The proposed reconstruction method is faster, more precise, and significantly less influenced by systematic uncertainties, than the current one. This system provides a more robust estimate of angular uncertainties than the previous algorithm, making it a solid benchmark for real-time event analyses.

Authors:Cui-Yuan Dai, Xiang-Yu Wang, Ruo-Yu Liu, Bing Zhang

Abstract: Recent LHAASO observations of the prompt emission phase of the brightest-of-all-time GRB 221009A imposes a stringent limit on the flux ratio between the TeV and MeV emissions, $F_{\rm TeV}/F_{\rm MeV}\le 2\times10^{-5}$. Within the framework of internal shocks, we study the internal $\gamma\gamma$ absorption in GRB 221009A by generating a set of synthetic bursts in a simulation that reproduces the observed feature of GRB 221009A. We find that the $\gamma\gamma$ absorption does not lead to an exponential cutoff, but rather a power-law spectrum, consistent with previous works. We further find that the attenuation due to $\gamma\gamma$ absorption alone cannot explain the flux limit ratio of GRB 221009A, suggesting a low ratio of synchrotron self-Compton (SSC) to synchrotron emission outputs. This requires that the magnetic field energy density is much larger than the synchrotron photon energy density so that the SSC flux is greatly suppressed. This indicates that the jet composition of GRB 221009A is likely Poynting-flux-dominated.

Authors:R. Brogan, M. Krumpe, D. Homan, T. Urrutia, T. Granzer, B. Husemann, J. Neumann, M. Gaspari, S. P. Vaughan, S. M. Croom, F. Combes, M. Pérez Torres, A. Coil, R. McElroy, N. Winkel, M. Singha

Abstract: Changing-look active galactic nuclei (CL-AGN) have been observed to change optical spectral type. Mrk 1018 is unique: first classified as a type 1.9 Seyfert galaxy, it transitioned to a type 1 before returning to its initial classification after approximately 30 years. We present a high-cadence monitoring programme that caught a major outburst in 2020. Due to sunblock, only the decline could be observed. We studied X-ray, UV, optical, and IR before and after the outburst to investigate the responses of the AGN structures. We derived a u'-band light curve of the AGN contribution alone. The flux increased by a factor of the order of 13. We confirmed this in other optical bands and determined the shape and speed of the decline in each waveband. The shapes of H beta and H alpha were analysed before and after the event. Two XMM-Newton observations from before and after the outburst were also exploited. The outburst is asymmetric, with a swifter rise than decline. The decline is best fit by a linear function, ruling out a tidal disruption event. The optical spectrum shows no change approximately 8 months before and 17 months after. The UV flux increased slightly after the outburst but the X-ray primary flux is unchanged. However, the 6.4 keV Iron line has doubled in strength. IR data taken 13 days after the observed optical peak show an increased emission level. Calculating the distance of the broad-line region and inner edge of the torus from the supermassive black hole can explain the multi-wavelength response to the outburst, in particular: i) the unchanged H beta and H alpha lines, ii) the unchanged primary X-ray spectral components, iii) the rapid and extended infrared response, as well as iv) the enhanced emission of the reflected 6.4 keV line. The outburst was due to a dramatic and short-lasting change in the intrinsic accretion rate. We discuss different models as potential causes.

Authors:Andrew Kozhberov

Abstract: We study breaking properties of a solid neutron star crust. We consider the case in which the crust at any fixed density consists of two types ions, forming a strongly ordered Coulomb crystal. It is shown that the breaking stress of a such matter noticeably depends on ionic composition, and it is typically larger than for a one-component crystal. The difference may reach a factor of several.

Authors:Hao Li, Bo-Qiang Ma

Abstract: The Large High Altitude Air Shower Observatory~(LHAASO) reported observation of photons with energies above 10~TeV from gamma ray burst GRB221009A. A suggestion was proposed that this result may contradict with our knowledge of special relativity~(SR) and the standard model~(SM), according to which photons of about 10~TeV from such a distant object should be severely suppressed because of the absorption by extragalactic background light. As a result, a number of mechanisms have been proposed to solve this potential puzzle, including Lorentz invariance violation~(LIV). In this work, we perform a detailed numerical calculation and show the feasibility to constrain LIV of photons from the LHAASO observation of GRB221009A quantitatively.

Authors:Lucy Oswald, Aris Karastergiou, Simon Johnston

Abstract: The population of radio pulsars is observed to demonstrate certain polarization properties not explained by the conventional picture of pulsar polarization, namely frequency evolution of polarization, deviations of the linear polarization angle from a curve of geometric origins and the presence of features in the circular polarization. We present the partial-coherence model as a way to explain the co-occurrence of these features and to provide an origin for circular polarization in radio pulsar profiles. We describe the mathematics of the model and demonstrate how it can explain these observed features, both on a population level and for the idiosyncrasies of individual pulsars. The partial coherence model can account for complex polarization behaviour, enabling improved access to information about pulsar geometries. We discuss the scientific implications of this for our understanding of pulsar radio emission and propagation.

Authors:Kosuke Nishiwaki, Katsuaki Asano, Kohta Murase

Abstract: A fraction of merging galaxy clusters host diffuse radio emission in their central region, termed as a giant radio halo (GRH). The most promising mechanism of GRHs is the re-acceleration of non-thermal electrons and positrons by merger-induced turbulence. However, the origin of these seed leptons has been under debate, and either protons or electrons can be primarily-accelerated particles. In this work, we demonstrate that neutrinos can be used as a probe of physical processes in galaxy clusters, and discuss possible constraints on the amount of relativistic protons in the intra-cluster medium with the existing upper limits by IceCube. We calculate radio and neutrino emission from massive ($>10^{14}M_\odot$) galaxy clusters, using the cluster population model of Nishiwaki & Asano (2022). This model is compatible with the observed statistics of GRHs, and we find that the contribution of GRHs to the isotropic radio background observed with the ARCADE-2 experiment should be subdominant. Our fiducial model predicts the all-sky neutrino flux that is consistent with IceCube's upper limit from the stacking analysis. We also show that the neutrino upper limit gives meaningful constraints on the parameter space of the re-acceleration model, such as the electron-to-proton ratio of primary cosmic-rays and the magnetic field, and in particular the secondary scenario, where the seed electrons mostly originate from inelastic $pp$ collisions, can be constrained even in the presence of re-acceleration.

Authors:Sunil Malik, Ka Ho Yuen, Huirong Yan

Abstract: Magnetic fields are ubiquitous in the interstellar medium, including extended objects such as supernova remnants (SNRs) and Pulsar Wind Nebulae (PWNe). Its turbulent characteristics govern the diffusion of cosmic rays and the multi-wavelength emission from PWNe. However, the geometry and turbulence nature of the magnetic fields in the ambient region of PWN is still unknown. Recent gamma-ray observations from HAWC and synchrotron observations suggest a highly suppressed diffusion coefficient compared to the mean interstellar value. In this letter, we present the first direct observational evidence that the local mean magnetic field is nearly aligned toward the line of sight (LoS) with an inclination angle $\theta_{\lambda} <10^{\circ}$ employing a recently developed statistical recipe known as `Y-parameter'. Furthermore, we report that the magnetic field fluctuations are mostly dominated by compressible modes, with a 2D correlation length of approximately $3 \ {\rm pc}$ in the vicinity of Monogem PWN region. Our study highlights the pivotal role of magnetic field and turbulence in unraveling the physical processes in TeV halos and cosmic ray transport.

Authors:Y. X. Jane Yap, Albert Kong, Kwan Lok Li

Abstract: We report optical observations of the millisecond pulsar binary system PSR J1622-0315 with the Lulin 1m telescope in Taiwan and the Lijiang 2.4m telescope in China between 2019 and 2021. The companion of the pulsar, which is of V~19 mag, showed ellipsoidal-distorted orbital variations in its light curves. The best-fit model to the light curves, with the binary code PHOEBE, gives a companion mass of 0.122+/-0.006 M_sun. This places PSR J1622-0315 in the spider-system subclass. We compared the properties of PSR J1622-0315 with other spider pulsar binaries for the scalings between the spin-down luminosity derived for the pulsar, irradiation luminosity of the companion, and X-ray luminosity of the binary. We find that pulsar irradiation in PSR J1622-0315 is insignificant and the irradiation luminosity of the transitional millisecond pulsars PSR J1023+0038 and PSR J1227-4853 are the highest among the redback systems.

Authors:R. Bandiera, N. Bucciantini, B. Olmi, D. F. Torres

Abstract: The vast majority of Pulsar Wind Nebulae (PWNe) present in the Galaxy is formed by middle-aged systems characterized by a strong interaction of the PWN itself with the supernova remnant (SNR). Unfortunately, modelling these systems can be quite complex and numerically expensive, due to the non-linearity of the PWN-SNR evolution even in the simple 1D / one-zone case when the reverse shock of the SNR reaches the PWN, and the two begin to interact (and reverberation starts). Here we introduce a new numerical technique that couples the numerical efficiency of the one-zone thin shell approach with the reliability of a full ``lagrangian'' evolution, able to correctly reproduce the PWN-SNR interaction during the reverberation and to consistently evolve the particle spectrum beyond. Based on our previous findings, we show that our novel strategy resolves many of the uncertainties present in previous approaches, as the arbitrariness in the SNR structure, and ensure a robust evolution, compatible with results that can be obtained with more complex 1D dynamical approaches. Our approach enable us for the first time to provide reliable spectral models of the later compression phases in the evolution of PWNe. While in general we found that the compression is less extreme than that obtained without such detailed dynamical considerations, leading to the formation of less structured spectral energy distributions, we still find that a non negligible fraction of PWNe might experience a super-efficient phase, with the optical and/or X-ray luminosity exceeding the spin-down one.

Authors:Sandro Mereghetti, Michela Rigoselli, Ruben Salvaterra, Andrea Tiengo, Dominik Pacholski

Abstract: 230307A is the second brightest gamma ray burst detected in more than 50 years of observations and is located in the direction of the Magellanic Bridge. Despite its long duration, it is most likely the result of the compact merger of a binary ejected from a galaxy in the local universe (redshift z=0.065). Our XMM-Newton observation of its afterglow at 4.5 days shows a power-law spectrum with photon index $\Gamma =1.73 \pm0.10$, unabsorbed flux $F_{0.3-10\,\rm keV}=(8.8\pm0.5)\times 10^{-14}$ erg cm$^{-2}$ s$^{-1}$ and no absorption in excess of that produced in our Galaxy and in the Magellanic Bridge. We derive a limit of $N_{\rm H}^{\rm HOST} < 5\times 10^{20}$ cm$^{-2}$ on the absorption at the GRB redshift, which is a factor $\sim\,$5 below the value measured during the prompt phase. We searched for the presence of dust scattering rings with negative results and set an upper limit of the order of $A_V<0.05$ on the absorption from dust in the Magellanic Bridge.

Authors:M. Razzano, A. Fiori, P. M. Saz Parkinson, R. P. Mignani, A. De Luca, A. K. Harding, M. Kerr, M. Marelli, V. Testa

Abstract: Context. We have investigated the multiwavelength emission of PSR J2021+4026, the only isolated gamma-ray pulsar known to be variable, which in October 2011 underwent a simultaneous change in gamma-ray flux and spin-down rate, followed by a second mode change in February 2018. Multiwavelength monitoring is crucial to understand the physics behind these events and how they may have affected the structure of the magnetosphere. Aims.The monitoring of pulse profile alignment is a powerful diagnostic tool for constraining magnetospheric reconfiguration. We aim to investigate timing or flux changes related to the variability of PSR J2021+4026 via multiwavelength observations, including gamma-ray observations from Fermi-LAT, X-ray observations from XMM-Newton, and a deep optical observation with the Gran Telescopio Canarias.Methods. We performed a detailed comparison of the timing features of the pulsar in gamma and X-rays and searched for any change in phase lag between the phaseogram peaks in these two energy bands. Although previous observations did not detect a counterpart in visible light, we also searched for optical emission that might have increased due to the mode change, making this pulsar detectable in the optical. Results.We have found a change in the gamma-to X-ray pulse profile alignment by 0.21$\pm$0.02 in phase, which indicates that the first mode change affected different regions of the pulsar magnetosphere. No optical counterpart was detected down to g'=26.1 and r'=25.3. Conclusions.We suggest that the observed phase shift could be related to a reconfiguration of the connection between the quadrupole magnetic field near the stellar surface and the dipole field that dominates at larger distances. This is consistent with the picture of X-ray emission coming from the heated polar cap and with the simultaneous flux and frequency derivative change observed during the mode changes.

Authors:Blagoy Rangelov, Hui Yang, Brice Williams, Oleg Kargaltsev, Jeremy Hare, Kean Martinic

Abstract: In the latest data release from the Fermi $\gamma$-Ray Space Telescope (the 4th Fermi LAT 12-year Catalog or 4FGL) more than 50% of the Galactic sources are yet to be identified. We observed thirteen unidentified Fermi LAT sources with Chandra X-Ray Observatory (CXO) to explore their nature. We report the results of the classification of X-ray sources in the fields of these $\gamma$-ray sources and discuss the implications for their nature. We use the multiwavelength (MW) data for machine-learning classification accompanied by a more detailed spectral/variability analysis for brighter sources. Seven 4FGL sources have $\gamma$-ray pulsars within their position error ellipses. Three of these pulsars are either detected in the CXO images or show hints of X-ray emission. Within the positional uncertainties of three 4FGL sources we detect X-ray sources that may be yet unknown pulsars, depending on the MW association. In addition to point sources, we discovered 2 extended sources one of which is likely to be a bowshock pulsar-wind nebula associated with PSR J1358.3-6026. Finally, we classify other X-ray sources detected in these observations and report most interesting classifications.

Authors:João R. T. de Mello Neto

Abstract: Ultra-high-energy cosmic neutrinos (UHE), with energies above 100 PeV, are unparalleled probes of the most energetic astrophysical sources and weak interactions at energies beyond the reach of accelerators. GRAND is an envisioned observatory of UHE particles - neutrinos, cosmic rays, and gamma rays - consisting of 200,000 radio antennas deployed in sub-arrays at different locations worldwide. GRAND aims to detect the radio emission from air showers induced by UHE particle interactions in the atmosphere and underground. For neutrinos, it aims to reach a flux sensitivity of $\sim 10^{-10}$ GeV cm$^{-2}$ s$^{-1}$ sr$^{-1}$, with a sub-degree angular resolution, which would allow it to test the smallest predicted diffuse fluxes of UHE neutrinos and to discover point sources. The GRAND Collaboration operates three prototype detector arrays simultaneously: GRAND@Nan\c{c}ay in France, GRANDProto300 in China, and GRAND@Auger in Argentina. The primary purpose of GRAND@Nan\c cay is to serve as a testbench for hardware and triggering systems. On the other hand, GRANDProto300 and GRAND@Auger are exploratory projects that pave the way for future stages of GRAND. GRANDProto300 is being built to demonstrate autonomous radio-detection of inclined air showers and study cosmic rays near the proposed transition between galactic and extragalactic sources. All three arrays are in the commissioning stages. It is expected that by 2028, the detector units of the final design could be produced and deployed, marking the establishment of two GRAND10k arrays in the Northern and Southern hemispheres. We will survey preliminary designs, simulation results, construction plans, and the extensive research program made possible by GRAND.

Authors:P. Short, A. Lawrence, M. Nicholl, M. Ward, T. M. Reynolds, S. Mattila, C. Yin, I. Arcavi, A. Carnall, P. Charalampopoulos, M. Gromadzki, P. G. Jonker, S. Kim, G. Leloudas, I. Mandel, F. Onori, M. Pursiainen, S. Schulze, C. Villforth, T. Wevers

Abstract: Tidal disruption events (TDEs) occur when a star gets torn apart by a supermassive black hole as it crosses its tidal radius. We present late-time optical and X-ray observations of the nuclear transient AT2019qiz, which showed the typical signs of an optical-UV transient class commonly believed to be TDEs. Optical spectra were obtained 428, 481 and 828 rest-frame days after optical lightcurve peak, and a UV/X-ray observation coincided with the later spectrum. The optical spectra show strong coronal emission lines, including [Fe VII], [Fe X], [Fe XI] and [Fe XIV]. The Fe lines rise and then fall, except [Fe XIV] which appears late and rises. We observe increasing flux of narrow H-alpha and H-beta and a decrease in broad H-alpha flux. The coronal lines have FWHMs ranging from ~150 - 300km/s, suggesting they originate from a region between the broad and narrow line emitting gas. Between the optical flare and late-time observation, the X-ray spectrum softens dramatically. The 0.3-1 keV X-ray flux increases by a factor of ~50 while the hard X-ray flux decreases by a factor of ~6. WISE fluxes also rose over the same period, indicating the presence of an infrared echo. With AT2017gge, AT2019qiz is one of two examples of a spectroscopically-confirmed optical-UV TDE showing delayed coronal line emission, supporting speculations that Extreme Coronal Line Emitters in quiescent galaxies can be echos of unobserved past TDEs. We argue that the coronal lines, narrow lines, and infrared emission arise from the illumination of pre-existing material likely related to either a previous TDE or AGN activity.

Authors:J. Ballet, P. Bruel, T. H. Burnett, B. Lott, The Fermi-LAT collaboration

Abstract: We present an incremental version (4FGL-DR4, for Data Release 4) of the fourth Fermi-LAT catalog of gamma-ray sources. Based on the first 14 years of science data in the energy range from 50 MeV to 1 TeV, it uses the same analysis methods as the 4FGL-DR3 catalog did for 12 years of data, with only a few improvements. The spectral parameters, spectral energy distributions, light curves and associations are updated for all sources. We add four new extended sources and modify two existing ones. Among the 6658 4FGL-DR3 sources, we delete 14 and change the localization of 10, while 26 are newly associated and two associations were changed. We add 546 point sources, among which 8 are considered identified and 228 have a plausible counterpart at other wavelengths. Most are just above the detection threshold, and 14 are transient sources below the detection threshold that can affect the light curves of nearby sources.

Authors:Hai-Ming Zhang, Yi-Yun Huang, Ruo-Yu Liu, Xiang-Yu Wang

Abstract: Recently, LHAASO reported the detection of brightest-of-all-time GRB 221009A, revealing the early onset of a TeV afterglow. However, there is no evidence of afterglow emission at such early time at other wavelengths. Here we report the discovery of a hidden afterglow component during the prompt emission phase with Fermi Gamma-Ray Burst Monitor (GBM) observations. We analyze the spectral evolution of the X-ray/$\gamma$-ray emission of GRB 221009A measured by GBM during the dips of two prompt emission pulses (i.e., intervals $T_{0}+[300-328]\rm~s$ and $T_{0}+[338-378]\rm~s$, where $T_0$ is the GBM trigger time). We find that the spectra at the dips transit from the Band function to a power-law function, indicating a transition from the prompt emission to the afterglow. After $\sim T_{0}+ 660 \rm~s$, the spectrum is well described by a power-law function and the afterglow becomes dominant. Remarkably, the underlying afterglow emission at the dips smoothly connect with the afterglow after $\sim T_{0}+ 660 \rm~s$. The entire afterglow emission measured by GBM can be fitted by a power-law function $F\sim t^{-0.95\pm0.05}$, where $t$ is the time since the first main pulse at $T^*=T_0+226~{\rm s}$, consistent with the TeV afterglow decay measured by LHAASO. The start time of this power-law decay indicates that the afterglow peak of GRB 221009A should be earlier than $T_{0}+300 \rm ~s$. We also test the possible presence of a jet break in the early afterglow light curve, finding that both the jet break model and single power-law decay model are consistent with the GBM data. The two models can not be distinguished with the GBM data alone because the inferred jet break time is quite close to the end of GBM observations.

Authors:Ruican Ma, Mariano Mendez, Federico Garcia, Na Sai, Liang Zhang, Yuexin Zhang

Abstract: We analyze a Neutron Star Interior Composition Explorer (NICER) observation of the black hole X-ray binary MAXI J1820+070 during a transition from type-C to type-B quasi-periodic oscillations (QPOs). We find that below ~2 keV, for the type-B QPOs the rms amplitude is lower and the magnitude of the phase lags is larger than for the type-C QPOs. Above that energy, the rms and phase-lag spectra of the type-B and type-C QPOs are consistent with being the same. We perform a joint fit of the time-averaged spectra of the source, and the rms and phase-lag spectra of the QPOs with the time-dependent Comptonization model vkompth to study the geometry of the corona during the transition. We find that the data can be well-fitted with a model consisting of a small and a large corona that are physically connected. The sizes of the small and large coronae increase gradually during the type-C QPO phase whereas they decrease abruptly at the transition to type-B QPO. At the same time, the inner radius of the disc moves inward at the QPO transition. Combined with simultaneous radio observations showing that discrete jet ejections happen around the time of the QPO transition, we propose that a corona that expands horizontally during the type-C QPO phase, from ~10^{4} km (~800 Rg) to ~10^{5} km (~8000 Rg) overlying the accretion disc, transforms into a vertical jet-like corona extending over ~10^{4} km (~800 Rg) during the type-B QPO phase.

Authors:Andrey Saveliev, Rafael Alves Batista

Abstract: Lorentz invariance violation (LIV) is a proposed phenomenon where Lorentz symmetry is violated at high energies, potentially affecting particle dynamics and interactions. We use numerical simulations with the CRPropa framework to investigate LIV in gamma-ray-induced electromagnetic cascades, specifically studying how it impacts cascading electrons and photons undergoing pair production and inverse Compton scattering. Our detailed analysis of the simulation results, compared with existing theoretical models, reveals that LIV can significantly alter the behavior of both components of the cascade, photons and electrons, resulting in specific signatures in measured fluxes that could be observed in high-energy gamma-ray observations. These insights are crucial for ongoing searches for LIV and for the development of theoretical models incorporating LIV effects.

Authors:Divya Rawat, Nazma Husain, Ranjeev Misra

Abstract: We investigate spectro-temporal properties for two black hole X-ray binary sources, MAXI J1535$-$571 and H 1743$-$322, during their hard and hard-intermediate states. For MAXI J1535$-$571, we analyze Swift/XRT, NuSTAR and NICER observations, specifically focusing on the occurrence of type-C Quasi-periodic Oscillations (QPOs). Regarding H 1743$-$322, we analyze multi-epoch observations of NICER and AstroSat, identifying a type-C QPO with centroid frequency ranging from 0.1--0.6 Hz. In both sources, we fit the spectra with a relativistic truncated disk and a power law component. In MAXI J1535$-$571, we also observe an additional relativistically smeared iron line. Through temporal and spectral analysis, we estimate the QPO centroid frequency and spectral parameters, such as the accretion rate and inner disc radii. We test the origin of type-C QPOs as relativistic precession frequency and dynamic frequency (i.e. the inverse of the sound crossing time $\frac{r}{c_s(r)}$). The dependence of QPO frequency on both the accretion rate and inner disc radii favours the QPO origin as dynamic frequency. We discuss the implications of these results.

Authors:Marina Orio, Keith Gendreau, Morgan Giese, Gerardo Juna M. Luna, Jozef Magdolen, Tod E. Strohmayer, Andy E. Zhang, Diego Altamirano, Andrej Dobrotka, Teruaki Enoto, Elizabeth C. Ferrara, Richard Ignace, Sebastian heinz, Craig Markwardt, Joy S. Nichols, Micahel L. Parker, Dheerajay R. Pasham, Songpeng Pei, Pragati Pradhan, Ron Remillard, James F. Steiner, Francesco Tombesi

Abstract: The 2021 outburst of the symbiotic recurrent nova RS Oph was monitored with the Neutron Star Interior Composition Explorer Mission (NICER) in the 0.2-12 keV range from day one after the optical maximum, until day 88, producing an unprecedented, detailed view of the outburst development. The X-ray flux preceding the supersoft X-ray phase peaked almost 5 days after optical maximum and originated only in shocked ejecta for 21 to 25 days. The emission was thermal; in the first 5 days only a non-collisional-ionization equilibrium model fits the spectrum, and a transition to equilibrium occurred between days 6 and 12. The ratio of peak X-rays flux measured in the NICER range to that measured with Fermi in the 60 MeV-500 GeV range was about 0.1, and the ratio to the peak flux measured with H.E.S.S. in the 250 GeV-2.5 TeV range was about 100. The central supersoft X-ray source (SSS), namely the shell hydrogen burning white dwarf (WD), became visible in the fourth week, initially with short flares. A huge increase in flux occurred on day 41, but the SSS flux remained variable. A quasi-periodic oscillation every ~35 s was always observed during the SSS phase, with variations in amplitude and a period drift that appeared to decrease in the end. The SSS has characteristics of a WD of mass >1 M(solar). Thermonuclear burning switched off shortly after day 75, earlier than in 2006 outburst. We discuss implications for the nova physics.

Authors:Pasquale Blasi GSSI

Abstract: The theory of transport of charged particles in cosmic magnetic fields is at the very center of the investigation of non-thermal phenomena in the universe, ranging from our local neighborhood to supernovae, clusters of galaxies or distant active galaxies. It is crucial to understand how particles get energized to non-thermal energies as well as to describe their motion from the sources to an observer or to another location in the universe. Here I summarize some essential, basic aspects of the theory and discuss some topics in the theoretical framework that are currently being developed. I will also discuss some simple applications of the theory of transport to particle acceleration and propagation in the Galaxy.

Authors:Pasquale Blasi GSSI, Giovanni Morlino INAF/Arcetri

Abstract: Cosmic ray acceleration at the termination shock of compact star clusters has recently received much attention, mainly because of the detection of gamma ray emission from some of such astrophysical sources. Here we focus on the acceleration of nuclei at the termination shock and we investigate the role played by proton energy losses and spallation reactions of nuclei, especially downstream of the shock. We show that for a rather generic choice of the mean gas density in the cavity excavated by the cluster wind, the spectrum of He nuclei is systematically harder than the spectrum of hydrogen, in a manner that appears to be qualitatively consistent with the observed and yet unexplained phenomenon of discrepant hardening. We also find that the spallation reactions of heavier nuclei are likely to be so severe that their spectra become very hard and with a low normalization, meaning that it is unlikely that heavy nuclei escaping star clusters can provide a sizeable contribution to the spectrum of cosmic rays at the Earth.

Authors:Sagar Adhikari, Pablo Penil, John Ryan Westernacher-Schneider, Alberto Dominguez, Marco Ajello, Sara Buson, Alba Rico, Jonathan Zrake

Abstract: PG 1553+113 is a well-known blazar exhibiting evidence of a $\sim\! 2.2$-year quasi-periodic oscillation in radio, optical, X-ray, and $\gamma$-ray bands. We present evidence of a new, longer oscillation of $21.8 \pm 4.7$ years in its historical optical light curve covering 100 years of observation. On its own, this $\sim\! 22$-year period has a statistical significance of $1.9\sigma$ when accounting for the look-elsewhere effect. However, the probability of both the $2.2$- and $22$-year periods arising from noise is $\sim0.02\%$ ($3.5\sigma$). The next peak of the 22-year oscillation should occur around July 2025. We find that the $\sim\,$10:1 relation between these two periods can arise in a plausible supermassive black hole binary model. Our interpretation of PG 1553+113's two periods suggests that the binary engine has a mass ratio $\gtrsim 0.2$, an eccentricity $\lesssim 0.1$, and accretes from a disk with characteristic aspect ratio $\sim 0.03$. The putative supermassive black hole binary radiates nHz gravitational waves, but the amplitude is $\sim10-100$ times too low for detection by foreseeable pulsar timing arrays.

Authors:Orhan Donmez

Abstract: Studying the gravitational collapse of dust particles toward newly formed black holes has gained popularity following the observation of gravitational waves resulting from the merger of black holes. In this paper, we focus on modelling the descent of dust debris toward a black hole using a numerical code that incorporates relativistic hydrodynamics in the framework of General and Einstein-Gauss Bonnet gravity. We explore the influence of various parameters, such as the black hole's rotation parameter a and the EGB coupling constant alpha, on the curvature effects observed. Both parameters significantly impact the dynamics of the accretion disk formed around the black holes. Furthermore, we discuss the gravitational collapsing process in two distinct scenarios. It is also observed that the mass accretion rate is significantly influenced by these two parameters. The rate at which mass is accreted toward a black hole directly impacts the black hole's growth and evolutionary trajectory.

Authors:Shi-Jie Gao, Xiang-Dong Li

Abstract: Observations of elliptical galaxies suggest that black holes (BHs) might serve as dark energy candidates, coupled to the expansion of the Universe. According to this hypothesis, the mass of a BH could increase as the Universe expands. BH low-mass X-ray binaries (LMXBs) in the Galactic disk were born several gigayears ago, making the coupling effect potentially significant. In this work, we calculate the evolution of BH binaries with a binary population synthesis method to examine the possible influence of cosmologically-coupled growth of BHs, if it really exists. The measured masses of the compact objects in LMXBs show a gap around $\sim 2.5-5~{\rm M_\odot}$, separating the most massive neutron stars from the least massive BHs. Our calculated results indicate that, considering the mass growth seem to (partially) account for the mass gap and the formation of compact BH LMXBs, alleviating the challenges in modeling the formation and evolution of BH LMXBs with traditional theory. However, critical observational evidence like the detection of intermediate-mass black hole binaries is required to test this hypothesis.

Authors:Wynn C. G. Ho Haverford, Nils Andersson Southampton

Abstract: Previous theoretical works using the pre-merger orbital evolution of coalescing neutron stars to constrain properties of dense nuclear matter assume a gravitational wave phase uncertainty of a few radians, or about a half cycle. However, recent studies of the signal from GW170817 and next generation detector sensitivities indicate actual phase uncertainties at least twenty times better. Using these refined estimates, we show that future observations of nearby sources like GW170817 may be able to reveal neutron star properties beyond just radius and tidal deformability, such as the matter composition and/or presence of a superfluid inside neutron stars, via tidal excitation of g-mode oscillations. Data from GW170817 already limits the amount of orbital energy that is transferred to the neutron star to <2x10^47 erg and the g-mode tidal coupling to Qmode<10^-3 at 50 Hz (5x10^48 erg and 4x10^-3 at 200 Hz), and future observations and detectors will greatly improve upon these constraints. In addition, analysis using general parameterization models that have been applied to the so-called p-g instability show that the instability already appears to be restricted to regimes where the mechanism is likely to be inconsequential; in particular, we show that the number of unstable modes is <<100 at <~100 Hz, and next generation detectors will essentially rule out this mechanism (assuming that the instability remains undetected). Finally, we illustrate that measurements of tidal excitation of r-mode oscillations in nearby rapidly rotating neutron stars are within reach of current detectors and note that even non-detections will limit the inferred inspiralling neutron star spin rate to <20 Hz, which will be useful when determining other parameters such as neutron star mass and tidal deformability.

Authors:Nijil Mankuzhiyil, Massimo Persic, Alberto Franceschini

Abstract: The Extragalactic Background Light (EBL) that spans the UV-IR band originates from direct and dust-reprocessed starlight integrated over the history of the Universe. EBL measurements are very challenging due to foreground emission like the zodiacal light and interplanetary dust emission. Indeed, some optical/NIR direct measurements overpredict EBL models based on galaxy counts. On the other hand, there is some debate on possible additional components of the Optical-NIR photon density: e.g., population-III stars, axion-photon decay, direct collapse of black holes, intra-halo light etc. Owing to the absorption of Very High Energy (VHE) $\gamma$ rays by interaction with EBL photons, we study the prospects of accommodating an additional population of EBL sources in the Optical-NIR band on top of the standard galaxy-count--based component. To this aim we use 105 VHE spectra of 37 blazars with known redshifts, $0.03<z<0.94$. We correct the observed spectra for absorption by our model EBL. By requiring the intrinsic spectra to be non-concave and with a VHE spectral index $>$1.5, we estimate, at different wavelengths, upper limits to the additional low energy photon fields which would contribute to the absorption of $\gamma$-rays. Considering these limits we suggest that there is room for photons from Pop III stars and axion-like particle (ALP) annihilation. However, these additional hypothetical photon fields are bound to fall significantly below direct published EBL measurements by several instruments, and therefore our limits are either in tension or even inconsistent with such measurements.

Authors:Nazma Husain, Yash Bhargava, Akash Garg, Sneha Prakash Mudambi, Ranjeev Misra, Somasri Sen

Abstract: 4U 1543-47 underwent its brightest outburst in 2021 after two decades of inactivity. During its decay phase, AstroSat conducted nine observations of the source spanning from July $1^{st}$ to September $26^{th}$, 2021. The first three observations were performed with an offset of 40 arcmin with AstroSat/LAXPC, while the remaining six were on-axis observations. In this report, we present a comprehensive spectral analysis of the source as it was in the High/Soft state during the entire observation period. The source exhibited a disk-dominated spectra with a weak high-energy tail (power-law index $\geq2.5$) and a high inner disk temperature ($\sim$0.84 keV). Modelling the disk continuum with non-relativistic and relativistic models, we find inner radius to be significantly truncated at $>$$10~R_g$. Alternatively, to model the spectral evolution with the assumption that the inner disk is at the ISCO, it is necessary to introduce variation in the spectral hardening in the range $\sim$1.5-1.9.

Authors:The Pierre Auger Collaboration, A. Abdul Halim, P. Abreu, M. Aglietta, I. Allekotte, K. Almeida Cheminant, A. Almela, J. Alvarez-Muñiz, J. Ammerman Yebra, G. A. Anastasi, L. Anchordoqui, B. Andrada, S. Andringa, C. Aramo, P. R. Araújo Ferreira, E. Arnone, J. C. Arteaga Velázquez, H. Asorey, P. Assis, G. Avila, E. Avocone, A. M. Badescu, A. Bakalova, A. Balaceanu, F. Barbato, J. A. Bellido, C. Berat, M. E. Bertaina, G. Bhatta, P. L. Biermann, V. Binet, K. Bismark, T. Bister, J. Biteau, J. Blazek, C. Bleve, J. Blümer, M. Boháčová, D. Boncioli, C. Bonifazi, L. Bonneau Arbeletche, N. Borodai, J. Brack, T. Bretz, P. G. Brichetto Orchera, F. L. Briechle, P. Buchholz, A. Bueno, S. Buitink, M. Buscemi, M. Büsken, A. Bwembya, K. S. Caballero-Mora, L. Caccianiga, I. Caracas, R. Caruso, A. Castellina, F. Catalani, G. Cataldi, L. Cazon, M. Cerda, J. A. Chinellato, J. Chudoba, L. Chytka, R. W. Clay, A. C. Cobos Cerutti, R. Colalillo, A. Coleman, M. R. Coluccia, R. Conceição, A. Condorelli, G. Consolati, M. Conte, F. Contreras, F. Convenga, D. Correia dos Santos, P. J. Costa, C. E. Covault, M. Cristinziani, C. S. Cruz Sanchez, S. Dasso, K. Daumiller, B. R. Dawson, R. M. de Almeida, J. de Jesús, S. J. de Jong, J. R. T. de Mello Neto, I. De Mitri, J. de Oliveira, D. de Oliveira Franco, F. de Palma, V. de Souza, E. De Vito, A. Del Popolo, O. Deligny, L. Deval, A. di Matteo, M. Dobre, C. Dobrigkeit, J. C. D'Olivo, L. M. Domingues Mendes, R. C. dos Anjos, J. Ebr, M. Emam, R. Engel, I. Epicoco, M. Erdmann, A. Etchegoyen, H. Falcke, J. Farmer, G. Farrar, A. C. Fauth, N. Fazzini, F. Feldbusch, F. Fenu, A. Fernandes, B. Fick, J. M. Figueira, A. Filipčič, T. Fitoussi, B. Flaggs, T. Fodran, T. Fujii, A. Fuster, C. Galea, C. Galelli, B. García, H. Gemmeke, F. Gesualdi, A. Gherghel-Lascu, P. L. Ghia, U. Giaccari, M. Giammarchi, J. Glombitza, F. Gobbi, F. Gollan, G. Golup, M. Gómez Berisso, P. F. Gómez Vitale, J. P. Gongora, J. M. González, N. González, I. Goos, D. Góra, A. Gorgi, M. Gottowik, T. D. Grubb, F. Guarino, G. P. Guedes, E. Guido, S. Hahn, P. Hamal, M. R. Hampel, P. Hansen, D. Harari, V. M. Harvey, A. Haungs, T. Hebbeker, D. Heck, C. Hojvat, J. R. Hörandel, P. Horvath, M. Hrabovský, T. Huege, A. Insolia, P. G. Isar, P. Janecek, J. A. Johnsen, J. Jurysek, A. Kääpä, K. H. Kampert, B. Keilhauer, A. Khakurdikar, V. V. Kizakke Covilakam, H. O. Klages, M. Kleifges, J. Kleinfeller, F. Knapp, N. Kunka, B. L. Lago, N. Langner, M. A. Leigui de Oliveira, V. Lenok, A. Letessier-Selvon, I. Lhenry-Yvon, D. Lo Presti, L. Lopes, R. López, L. Lu, Q. Luce, J. P. Lundquist, A. Machado Payeras, M. Majercakova, D. Mandat, B. C. Manning, J. Manshanden, P. Mantsch, S. Marafico, F. M. Mariani, A. G. Mariazzi, I. C. Mariş, G. Marsella, D. Martello, S. Martinelli, O. Martínez Bravo, M. A. Martins, M. Mastrodicasa, H. J. Mathes, J. Matthews, G. Matthiae, E. Mayotte, S. Mayotte, P. O. Mazur, G. Medina-Tanco, J. Meinert, D. Melo, A. Menshikov, S. Michal, M. I. Micheletti, L. Miramonti, S. Mollerach, F. Montanet, L. Morejon, C. Morello, A. L. Müller, K. Mulrey, R. Mussa, M. Muzio, W. M. Namasaka, A. Nasr-Esfahani, L. Nellen, G. Nicora, M. Niculescu-Oglinzanu, M. Niechciol, D. Nitz, I. Norwood, D. Nosek, V. Novotny, L. Nožka, A Nucita, L. A. Núñez, C. Oliveira, M. Palatka, J. Pallotta, G. Parente, A. Parra, J. Pawlowsky, M. Pech, J. Pękala, R. Pelayo, L. A. S. Pereira, E. E. Pereira Martins, J. Perez Armand, C. Pérez Bertolli, L. Perrone, S. Petrera, C. Petrucci, T. Pierog, M. Pimenta, M. Platino, B. Pont, M. Pothast, M. Pourmohammad Shavar, P. Privitera, M. Prouza, A. Puyleart, S. Querchfeld, J. Rautenberg, D. Ravignani, M. Reininghaus, J. Ridky, F. Riehn, M. Risse, V. Rizi, W. Rodrigues de Carvalho, J. Rodriguez Rojo, M. J. Roncoroni, S. Rossoni, M. Roth, E. Roulet, A. C. Rovero, P. Ruehl, A. Saftoiu, M. Saharan, F. Salamida, H. Salazar, G. Salina, J. D. Sanabria Gomez, F. Sánchez, E. M. Santos, E. Santos, F. Sarazin, R. Sarmento, R. Sato, P. Savina, C. M. Schäfer, V. Scherini, H. Schieler, M. Schimassek, M. Schimp, F. Schlüter, D. Schmidt, O. Scholten, H. Schoorlemmer, P. Schovánek, F. G. Schröder, J. Schulte, T. Schulz, S. J. Sciutto, M. Scornavacche, A. Segreto, S. Sehgal, S. U. Shivashankara, G. Sigl, G. Silli, O. Sima, R. Smau, R. Šmída, P. Sommers, J. F. Soriano, R. Squartini, M. Stadelmaier, D. Stanca, S. Stanič, J. Stasielak, P. Stassi, M. Straub, A. Streich, M. Suárez-Durán, T. Suomijärvi, A. D. Supanitsky, Z. Szadkowski, A. Tapia, C. Taricco, C. Timmermans, O. Tkachenko, P. Tobiska, C. J. Todero Peixoto, B. Tomé, Z. Torrès, A. Travaini, P. Travnicek, C. Trimarelli, M. Tueros, R. Ulrich, M. Unger, L. Vaclavek, M. Vacula, J. F. Valdés Galicia, L. Valore, E. Varela, A. Vásquez-Ramírez, D. Veberič, C. Ventura, I. D. Vergara Quispe, V. Verzi, J. Vicha, J. Vink, S. Vorobiov, C. Watanabe, A. A. Watson, A. Weindl, L. Wiencke, H. Wilczyński, D. Wittkowski, B. Wundheiler, A. Yushkov, O. Zapparrata, E. Zas, D. Zavrtanik, M. Zavrtanik

Abstract: A search for time-directional coincidences of ultra-high-energy (UHE) photons above 10 EeV with gravitational wave (GW) events from the LIGO/Virgo runs O1 to O3 is conducted with the Pierre Auger Observatory. Due to the distinctive properties of photon interactions and to the background expected from hadronic showers, a subset of the most interesting GW events is selected based on their localization quality and distance. Time periods of 1000 s around and 1 day after the GW events are analyzed. No coincidences are observed. Upper limits on the UHE photon fluence from a GW event are derived that are typically at $\sim$7 MeV cm$^{-2}$ (time period 1000~s) and $\sim$35 MeV cm$^{-2}$ (time period 1 day). Due to the proximity of the binary neutron star merger GW170817, the energy of the source transferred into UHE photons above 40 EeV is constrained to be less than 20% of its total gravitational wave energy. These are the first limits on UHE photons from GW sources.

Authors:Samuel J. Dunham, Eirik Endeve, Anthony Mezzacappa, John M. Blondin, Jesse Buffaloe, Kelly Holley-Bockelmann

Abstract: We present numerical results from a parameter study of the standing accretion shock instability (SASI), investigating the impact of general relativity (GR) on the dynamics. Using GR hydrodynamics and gravity, and non-relativistic (NR) hydrodynamics and gravity, in an idealized model setting, we vary the initial radius of the shock and, by varying its mass and radius in concert, the proto-neutron star (PNS) compactness. We investigate two regimes expected in a post-bounce core-collapse supernova (CCSN): one meant to resemble a relatively low-compactness configuration and one meant to resemble a relatively high-compactness configuration. We find that GR leads to a longer SASI oscillation period, with ratios between the GR and NR cases as large as 1.29 for the high-compactness suite. We also find that GR leads to a slower SASI growth rate, with ratios between the GR and NR cases as low as 0.47 for the high-compactness suite. We discuss implications of our results for CCSN simulations.

Authors:Amrutaa Vibho, Ali Al Bataineh

Abstract: The prediction of spin magnitudes in binary black hole and neutron star mergers is crucial for understanding the astrophysical processes and gravitational wave (GW) signals emitted during these cataclysmic events. In this paper, we present a novel Neuro-Symbolic Architecture (NSA) that combines the power of neural networks and symbolic regression to accurately predict spin magnitudes of black hole and neutron star mergers. Our approach utilizes GW waveform data obtained from numerical relativity simulations in the SXS Waveform catalog. By combining these two approaches, we leverage the strengths of both paradigms, enabling a comprehensive and accurate prediction of spin magnitudes. Our experiments demonstrate that the proposed architecture achieves an impressive root-mean-squared-error (RMSE) of 0.05 and mean-squared-error (MSE) of 0.03 for the NSA model and an RMSE of 0.12 for the symbolic regression model alone. We train this model to handle higher-order multipole waveforms, with a specific focus on eccentric candidates, which are known to exhibit unique characteristics. Our results provide a robust and interpretable framework for predicting spin magnitudes in mergers. This has implications for understanding the astrophysical properties of black holes and deciphering the physics underlying the GW signals.

Authors:Victor B. Valera, Mauricio Bustamante, Christian Glaser

Abstract: The discovery of ultra-high-energy (UHE) neutrinos has the potential to offer unique insight into fundamental questions. To capitalize on the upcoming opportunity provided by new UHE neutrino telescopes, we provide state-of-the-art forecasts of the discovery of a diffuse flux of UHE neutrinos over the next 10-20 years, focusing on neutrino radio-detection in the planned IceCube-Gen2 detector. We use state-of-the-art flux predictions and detector modeling. We find that, even under conservative analysis choices, most benchmark UHE neutrino flux models from the literature may be discovered within 10 years of detector exposure, with many discoverable sooner, and may be distinguished from each other. Our results demonstrate the transformative potential of next-generation UHE neutrino telescopes.

Authors:Shreya Anand, Peter T. H. Pang, Mattia Bulla, Michael W. Coughlin, Tim Dietrich, Brian Healy, Thomas Hussenot-Desenonges, Theophile Jegou du Laz, Mansi M. Kasliwal, Nina Kunert, Ivan Markin, Kunal Mooley, Vsevolod Nedora, Anna Neuweiler

Abstract: GW170817 and its associated electromagnetic counterpart AT2017gfo continue to be a treasure trove as observations and modeling continue. Recent precision astrometry of AT2017gfo with the Hubble Space Telescope combined with previous constraints from Very Long Baseline Interferometry (VLBI) constraints narrowed down the inclination angle to 19-25 deg (90\% confidence). This paper explores how the inclusion of precise inclination information can reveal new insights about the ejecta properties, in particular, about the composition of the dynamical ejecta of AT2017gfo. Our analysis relies on updated kilonova modeling, which includes state-of-the-art heating rates, thermalization efficiencies, and opacities and is parameterized by $\bar{Y}_{\rm e,dyn}$, the average electron fraction of the dynamical ejecta component. Using this model, we incorporate the latest inclination angle constraint of AT2017gfo into a light curve fitting framework to derive updated parameter estimates. Our results suggest that the viewing angle of the observer is pointed towards the lanthanide-poor ($Y_{\rm e,dyn}\gtrsim0.25$), squeezed polar dynamical ejecta component, which can explain the early blue emission observed in the light curve of AT2017gfo. In contrast to a recent claim of spherical ejecta powering AT2017gfo, our study indicates that the composition of the dynamical ejecta has a strong angular dependence, with a lanthanide-rich ($Y_{\rm e,dyn}\lesssim0.25$), tidal component distributed around the merger plane with a half-opening angle of $35^\circ$. The inclination angle constraint reduces $\bar{Y}_{\rm e,dyn}$ from $0.24$ to $0.22$, with values $0.17\lesssim Y_{\rm e, dyn} \lesssim0.41$ enabling the robust production of $r$-process elements up to the $3^{\rm rd}$ peak in the tidal dynamical ejecta.

Authors:Long Li, Shu-Qing Zhong, Zi-Gao Dai

Abstract: Whether binary neutron star mergers are the only astrophysical site of rapid neutron-capture process ($r$-process) nucleosynthesis remains unknown. Collapsars associated with long gamma-ray bursts (GRBs) and hypernovae are promising candidates. Simulations have shown that outflows from collapsar accretion disks can produce enough $r$-process materials to explain the abundances in the universe. However, there is no observational evidence to confirm this result at present. SN 2020bvc is a broad-lined type Ic (Ic-BL) supernova (SN) possibly associated with a low-luminosity GRB. Based on semi-analytic SN emission models with and without $r$-process materials, we perform a fitting to the multi-band light curves and photospheric velocities of SN 2020bvc. We find that in a $r$-process-enriched model the mixing of $r$-process materials slows down the photospheric recession and therefore matches the velocity evolution better. The fitting results show that $r$-process materials with mass of $\approx0.36~M_\odot$ and opacity of $\approx4~\rm cm^2~g^{-1}$ is needed to mix with about half of the SN ejecta. Our fitting results are weakly dependent on the nebular emission. Future statistical analysis of a sample of type Ic-BL SNe helps us understand the contribution of collapsars to the $r$-process abundance.

Authors:Hirotaka Ito, Jin Matsumoto, Shigehiro Nagataki, Donald C. Warren, Maxim V. Barkov, Daisuke Yonetoku

Abstract: We explore the properties of photospheric emission in the context of long gamma-ray bursts (LGRBs) using three numerical models that combine relativistic hydrodynamical simulations and Monte Carlo radiation transfer calculations in three dimensions. Our simulations confirm that the photospheric emission gives rise to correlations between the spectral peak energy and luminosity that agree with the observed Yonetoku, Amati, and Golenetskii correlations. It is also shown that the spectral peak energy and luminosity correlate with the bulk Lorentz factor, as indicated in the literature. On the other hand, synthetic spectral shapes tend to be narrower than those of the observations. The result indicates that an additional physical process that can provide non-thermal broadening is needed to reproduce the spectral features. Furthermore, the polarization analysis finds that, while the degree of polarization is low for the emission from the jet core ($\Pi < 4~\%$), it tends to increase with the viewing angle outside the core and can be as high as $\Pi \sim 20-40~\%$ in an extreme case. This suggests that the typical GRBs show systematically low polarization compared to softer, dimmer counterparts (X-ray-rich GRBs and X-ray flashes). Interestingly, our simulations indicate that photospheric emission exhibits large temporal variation in the polarization position angle ($\Delta \psi \sim 90^{\circ}$), which may be compatible with those inferred in observations. A notable energy dependence of the polarization property is another characteristic feature found in the current study. Particularly, the difference in the position angle among different energy bands can be as large as $\sim 90^{\circ}$.

Authors:A. Domínguez UC Madrid & IPARCOS, M. Láinez UC Madrid & IPARCOS, V. S. Paliya IUCAA, N. Álvarez-Crespo, M. Ajello, J. Finke, M. Nievas-Rosillo, J. L. Contreras, A. Desai

Abstract: The extragalactic high-energy $\gamma$-ray sky is dominated by blazars, which are active galactic nuclei with their jets pointing towards us. Distance measurements are of fundamental importance yet for some of these sources are challenging because any spectral signature from the host galaxy may be outshone by the non-thermal emission from the jet. In this paper, we present a method to constrain redshifts for these sources that relies only on data from the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. This method takes advantage of the signatures that the pair-production interaction between photons with energies larger than approximately 10 GeV and the extragalactic background light leaves on $\gamma$-ray spectra. We find upper limits for the distances of 303 $\gamma$-ray blazars, classified as 157 BL Lacertae objects, 145 of uncertain class, and 1 flat-spectrum-radio quasar, whose redshifts are otherwise unknown. These derivations can be useful for planning observations with imaging atmospheric Cherenkov telescopes and also for testing theories of supermassive black hole evolution. Our results are applied to estimate the detectability of these blazars with the future Cherenkov Telescope Array, finding that at least 21 of them could be studied in a reasonable exposure of 20 h.

Authors:Maxim Dvornikov IZMIRAN

Abstract: We study the gravitational scattering of ultrarelativistic neutrinos off a rotating supermassive black hole (BH) surrounded by a thick magnetized accretion disk. Neutrinos interact electroweakly with background matter and with the magnetic field in the disk since neutrinos are supposed to possess nonzero magnetic moments. The interaction with external fields results in neutrino spin oscillations. We find that the toroidal magnetic field, inherent in the magnetized Polish doughnut, does not cause a significant spin-flip for any reasonable strengths of the toroidal component. The reduction of the observed neutrino flux, owing to neutrino spin oscillations, is predicted. A poloidal component of the magnetic field gives the main contribution to the modification of the observed flux. The neutrino interaction with matter, rotating with relativistic velocities, also changes the flux of neutrinos. We briefly discuss the idea of the neutrino tomography of magnetic field distributions in accretion disks near BHs.

Authors:E. S. Yorgancioglu, Q. C. Bu, A. Santangelo, L. Tao, S. W. Davis, A. Vahdat, L. D. Kong, S. Piraino, M. Zhou, S. N. Zhang

Abstract: 4U 1543--47 is one of a handful of known black hole candidates located in the Milky Way Galaxy, and has undergone a very bright outburst in 2021, reaching a total of $\sim$9 Crab, as observed by the Monitor of All-sky Image (MAXI), and exceeding twice its Eddington luminosity. The unprecedented bright outburst of 4U 1543--47 provides a unique opportunity to test the behavior of accretion disk models at high luminosities and accretion rates. In addition, we explore the possibility of constraining the spin of the source at high accretion rates, given that previous spin measurements of 4U 1543--47 have been largely inconsistent with each other. We measure the spectral evolution of the source throughout its outburst as observed by Insight-HXMT, and compare the behavior of both the thin disk model kerrbb2, as well as the slim disk model slimbh up to the Eddington limit for two different values of disk $\alpha$-viscosity. In addition, given the behavior of these two models, we identify two `golden' epochs for which it is most suitable to measure the spin with continuum fitting.

Authors:V. Gayathri, I. Bartos, S. Rosswog, M. C. Miller, D. Veske, W. Lu, S. Marka

Abstract: Observations of compact objects in Galactic binaries have provided tentative evidence of a dearth of masses in the so-called lower mass gap $\sim2.2-5$ M$_\odot$. Nevertheless, two such objects have been discovered in gravitational-wave data from LIGO and Virgo. Remarkably, the estimated masses of both secondaries in the coalescences GW190814 ($m_2=2.59^{+0.08}_{-0.09}$M$_\odot$) and GW200210_092254 ($m_2=2.83^{+0.47}_{-0.42}$M$_\odot$) fall near the total mass of $\sim 2.6$ M$_\odot$ of observed Galactic binary neutron star systems. The more massive components of the two binaries also have similar masses. Here we show that a neutron star merger origin of the lighter components in GW190814 and GW200210_092254 is favored over $M^{-2.3}$ (Bayes factor $\mathcal{B}\sim 5$) and uniform ($\mathcal{B}\sim 14$) mass distributions in the lower mass gap. We also examine the statistical significance of the similarity between the heavier component masses of GW190814 and GW200210_092254, and find that a model in which the mass of GW200210_092254 is drawn from the mass posterior of GW190814 is preferred ($\mathcal{B}\sim 18$) to a model in which its mass is drawn from the overall mass distribution of black holes detected in gravitational wave events. This hints at a common origin of the primary masses, as well as the secondary masses, in GW190814 and GW200210_092254.

Authors:Damiano F. G. Fiorillo, Mauricio Bustamante

Abstract: The origin of the TeV--PeV astrophysical neutrinos seen by the IceCube telescope is unknown. If they are made in proton-photon interactions in astrophysical sources, their spectrum may show bump-like features. We search for such features in the 7.5-years High-Energy Starting Events (HESE), and forecast the power of such searches using larger data samples expected from upcoming telescopes. Present-day data reveals no evidence of bump-like features, which allows us to constrain candidate populations of photohadronic neutrino sources. Near-future forecasts show promising potential for stringent constraints or decisive discovery of bump-like features. Our results provide new insight into the origins of high-energy astrophysical neutrinos, complementing those from point-source searches.

Authors:M. Imbrogno, G. L. Israel, G. A. Rodríguez Castillo, D. A. H. Buckley, F. Coti Zelati, N. Rea, I. M. Monageng, P. Casella, L. Stella, F. Haberl, P. Esposito, F. Tombesi, A. De Luca, A. Tiengo

Abstract: During a systematic search for new X-ray pulsators in the XMM-Newton archive, we discovered a high amplitude ($PF\simeq86\%$) periodic ($P\simeq7.25\,\mathrm{s}$) modulation in the X-ray flux of 4XMM J045626.3-694723 (J0456 hereafter), a previously unclassified source in the Large Magellanic Cloud (LMC). The period of the modulation is strongly suggestive of a spinning neutron star (NS). The source was detected only during one out of six observations in 2018-2022. Based on an absorbed power-law spectral model with photon slope of $\Gamma\simeq 1.9$, we derive a 0.3-10 keV luminosity of $L_\mathrm{X}\simeq2.7\times10^{34}$ erg cm$^{-2}$ s$^{-1}$ for a distance of 50 kpc. The X-ray properties of J0456 are at variance with those of variable LMC X-ray pulsars hosted in high-mass X-ray binary systems with a Be-star companion. Based on SALT spectroscopic observations of the only optical object that matches the X-ray uncertainty region, we cannot completely rule out that J0456 is a NS accreting from a late-type (G8-K3) star, an as-yet-unobserved binary evolutionary outcome in the MCs. We show that the source properties are in better agreement with those of magnetars. J0456 may thus be second known magnetar in the LMC after SGR 0526-66.

Authors:Sergey Troitsky

Abstract: GRB 221009A was the brightest gamma-ray burst ever detected on Earth. In its early afterglow phase, photons with exceptional energies up to ~18 TeV were observed by LHAASO, and a photon-like air shower of ~251 TeV was detected by Carpet-2. Gamma rays at these high energies can hardly reach us from the distant GRB because of pair production on cosmic background radiation. A number of particle-physics solutions to this problem were discussed in recent months, and one of the most popular ones invokes the mixing of photons with axion-like particles (ALPs). Whether this is a viable scenario, depends crucially on the magnetic fields along the line of sight, which are poorly known. Here, we use the results of recent Hubble Space Telescope observations of the host galaxy of GRB 221009A, combined with magnetic-field measurements and simulations for other galaxies, to construct a toy model of the host-galaxy magnetic field and to estimate the rate of the photon-axion conversion there. Thanks, in particular, to the exceptional edge-on orientation of the host galaxy, strong mixing appears to be natural, both for 18-TeV and 251-TeV photons, for a wide range of ALP parameters.

Authors:Payaswini Saikia, David M. Russell, Saarah F. Pirbhoy, M. C. Baglio, M. Bramich, Kevin Alabarta, Fraser Lewis, Phil Charles

Abstract: We present a detailed study of optical data from the 2012 outburst of the candidate black hole X-ray binary Swift J1910.2-0546 using the Faulkes Telescope and Las Cumbres Observatory (LCO). We analyse the peculiar spectral state changes of Swift J1910.2-0546 in different energy bands, and characterise how the optical and UV emission correlates with the unusual spectral state evolution. Using various diagnostic tools like the optical/X-ray correlation and spectral energy distributions, we disentangle the different emission processes contributing towards the optical flux of the system. When Swift J1910.2-0546 transitions to the pure hard state, we find significant optical brightening of the source along with a dramatic change in the optical colour due to the onset of a jet during the spectral state transition. For the rest of the spectral states, the optical/UV emission is mostly dominated by an X-ray irradiated disk. From our high cadence optical study, we have discovered a putative modulation. Assuming that this modulation arises from a superhump, we suggest Swift J1910.2-0546 to have an orbital period of 2.25-2.47 hr, which would make it the shortest orbital period black hole X-ray binary known to date. Finally, from the state transition luminosity of the source, we find that the distance to the source is likely to be ~4.5-20.8 kpc, which is also supported by the comparative position of the source in the global optical/X-ray correlation of a large sample of black hole and neutron star X-ray binaries.

Authors:Maksat Satybaldiev, Ilya Mereminskiy, Alexander Lutovinov, Dmitri Karasev, Andrei Semena, Andrey Shtykovsky

Abstract: We present the results of the analysis of the SRG/ART-XC observation of the Supergiant Fast X-ray Transient IGR J16195-4545 performed on March 3, 2021. Six bright flares are present in the light curve, with no significant change in hardness occuring during these flares. The spectrum is described with an absorbed power law model with a high energy exponential cutoff showing heavy absorption, with $N_H=(12\pm2)\times 10^{22}\text{ cm}^{-2}$ and $\Gamma=0.56\pm 0.15$, $E_{cut}=13\pm 2$ keV. Adopting the Bayesian block decomposition of the light curve, we measured the properties of the observed flares (duration, rise time, waiting time, released energy and pre-flare luminosity), which are consistent with the quasi-spherical subsonic accretion model. The stellar wind velocity of the supergiant is estimated to be $v_{w} \approx 500$ km s$^{-1}$. Additionally, the system was found to have an unusual near-IR variability.

Authors:V. S. Beskin, V. I. Krauz, S. A. Lamzin

Abstract: Jets from young stars are used as an example to review how laboratory modeling enables advancement in understanding the main physical processes responsible for the formation and stability of these amazing objects. The discussion focuses on the options for modeling jet emissions in a laboratory experiment at the PF-3 facility at the National Research Center Kurchatov Institute. Many properties of the flows obtained using this experimental setup are consistent with the main features of jets from young stars.

Authors:N. T. Nguyen-Dang, G. Pühlhofer, M. Sasaki, A. Bamba, V. Doroshenko, A. Santangelo

Abstract: We report the results obtained from XMM-Newton observations of the TeV-detected supernova remnant (SNR) HESS J1534-571. We focus on the nature of the cosmic-ray particle content in the SNR, which is revealed by its $\gamma$-ray emission. No signatures of X-ray synchrotron emission were detected from the SNR. This is consistent with earlier results obtained with Suzaku from other regions of the object. A joint modeling of the XMM-Newton and Suzaku spectra yields an upper limit for the total X-ray flux from the SNR area of $\sim$ 5.62$ \times 10^{-13} \ \mathrm{erg\ cm^{-2}\ s^{-1}}$ (95% c.l.) in the energy band of 2-10 keV, for an assumed photon index of 2.0. On the other hand, we do find evidence in the XMM-Newton data for a line-like emission feature at 6.4 keV from localized regions, again confirming earlier Suzaku measurements. We discuss the findings in the context of the origin of the observed $\gamma$-ray emission. Although neither hadronic nor leptonic scenarios can be fully ruled out, the observed line emission can be interpreted as the result of interactions between lower energy ($\sim$ MeV) cosmic-ray protons with high gas density regions in and around HESS J1534-571, and thus potentially be associated with particles accelerated in the SNR.

Authors:Junhui Fan, Hubing Xiao, Wenxin Yang, Lixia Zhang, Anton A. Strigachev, Rumen S. Bachev, Jianghe Yang

Abstract: The studies and constraints on the emission region are crucial to the blazar radiation mechanism. Yet the previous works mainly focus on individual sources. In this work, we make use of the largest and the latest spectral energy distribution (SED) fitting results in the literature to statistically study the blazar emission region property in the framework of leptonic one-zone. Our results reveal (1) FSRQs show lower electron energy ($\gamma_{\rm p} \lesssim 1.6 \times 10^{3}$) than BL Lacs and tend to have a stronger magnetic field ($B$) and smaller electron-to-magnetic energy ratio ($U_{\rm e}/U_{\rm B}$) than BL Lacs; (2) we find the electro-magnetic equipartition would rather happen in the jets of BL Lacs than happen in the jets of FSRQs; (3) there are 682 blazars with a magnetic field weaker critical value of generating the Kelvin-Helmholtz instability, thus one-third of the blazars in our sample are able to produce this instability; (4) the distance ($d_{\rm em}$) between the emission region and the central black hole (BH) is in the scale of $\sim$0.1 pc, the location of the emission region may be evenly distributed inside and outside the broad line region (BLR).

Authors:A. Anker, P. Baldi, S. W. Barwick, J. Beise, D. Z. Besson, P. Chen, G. Gaswint, C. Glaser, A. Hallgren, J. C. Hanson, S. R. Klein, S. A. Kleinfelder, R. Lahmann, J. Liu, J. Nam, A. Nelles, M. P. Paul, C. Persichilli, I. Plaisier, R. Rice-Smith, J. Tatar, K. Terveer, S. -H Wang, L. Zhao

Abstract: The ARIANNA experiment is an Askaryan radio detector designed to measure high-energy neutrino induced cascades within the Antarctic ice. Ultra-high-energy neutrinos above $10^{16}$ eV have an extremely low flux, so experimental data captured at trigger level need to be classified correctly to retain more neutrino signal. We first describe two new physics-based neutrino selection methods, or "cuts", (the updown and dipole cut) that extend a previously published analysis to a specialized ARIANNA station with 8 antenna channels, which is double the number used in the prior analysis. The new cuts produce a neutrino efficiency of > 95% per station-year, while rejecting 99.93% of the background (corresponding to 53 remaining events). When the new cuts are combined with a previously developed cut using neutrino waveform templates, all background is removed at no change of efficiency. In addition, the neutrino efficiency is extrapolated to 1,000 station-years of operation, obtaining 91%. This work then introduces a new selection method (the deep learning cut) to augment the identification of neutrino events by using deep learning methods and compares the efficiency to the physics-based analysis. The deep learning cut gives 99% signal efficiency per station-year of operation while rejecting 99.997% of the background (corresponding to 2 remaining experimental background events), which are subsequently removed by the waveform template cut at no significant change in efficiency. The results of the deep learning cut were verified using measured cosmic rays which shows that the simulations do not introduce artifacts with respect to experimental data. The paper demonstrates that the background rejection and signal efficiency of near surface antennas meets the requirements of a large scale future array, as considered in baseline design of the radio component of IceCube-Gen2.

Authors:S. E. Pyatovsky

Abstract: The comparative primary cosmic rays (PCR) comparative analysis by E0 and the spectra of variable stars by periods is carried out in order to establish the causes of irregularities in the spectrum of PCR by E0. The relationship between the periods of variable stars and the maximum energy E0 of the nuclei of PCRs generated by these types of stars is shown. Irregularities in the PCR spectrum by E0 are associated with the transition from one dominant stars type to another. The knee in the PCR spectrum at E0 = 3-5 PeV is associated with a decrease in the contribution of SRB variability stars and a further increase in the contribution of Mira variable stars to the PCR flux. The bump in the PCR spectrum with a maximum at E0 = 80 PeV is formed by giant stars and super-giants of the Mira and SRC variability.

Authors:Taeho Ryu, Pau Amaro Seoane, Andrew M. Taylor, Sebastian T. Ohlmann

Abstract: In stellar-dense environments, stars can collide with each other. For collisions close to a supermassive black hole (SMBH), the collisional kinetic energy can be so large that the colliding stars can be completely destroyed, potentially releasing an amount of energy comparable to that of a supernova. These violent events have been examined mostly analytically, with the non-linear hydrodynamical effects being left largely unstudied. Using the moving-mesh hydrodynamics code {\small AREPO}, we investigate high-velocity ($>10^{3}$ km/s) collisions between 1M$_{\odot}$ giants with varying radii, impact parameters, and initial approaching velocities, and estimate their observables. Very strong shocks across the collision surface efficiently convert $\gtrsim10\%$ of the initial kinetic energy into radiation energy. The outcome is a gas cloud expanding supersonically, homologously, and quasi-spherically, generating a flare with a peak luminosity $\simeq 10^{41}-10^{44}$ erg/s in the extreme UV band ($\simeq 10$ eV). The luminosity decreases approximately following a power-law $t^{-0.7}$ initially, then $t^{-0.4}$ after $t\simeq$10 days at which point it would be bright in the optical band ($\lesssim 1$eV). Subsequent, and possibly even brighter, emission would be generated due to the accretion of the gas cloud onto the nearby SMBH, possibly lasting up to multi-year timescales. This inevitable BH-collision product interaction can contribute to the growth of BHs at all mass scales, in particular, seed BHs at high redshifts. Furthermore, the proximity of the events to the central BH makes them a potential tool for probing the existence of dormant BHs, even very massive ones which cannot be probed by tidal disruption events.

Authors:Vittoria Vecchiotti, Francesco L. Villante, Giulia Pagliaroli

Abstract: IceCube collaboration reported the first high-significance observation of the neutrino emission from the Galactic disk. The observed signal can be due to diffuse emission produced by cosmic rays interacting with interstellar gas but can also arise from a population of sources. In this paper, we evaluate both the diffuse and source contribution by taking advantage of gamma-ray observations and/or theoretical considerations. By comparing our expectations with IceCube measurement, we constrain the fraction of Galactic TeV gamma-ray sources (resolved and unresolved) with hadronic nature. In order to be compatible with the IceCube results, this fraction should be less than $\sim 40\%$ corresponding to a cumulative source flux $\Phi_{\nu, \rm s} \le 2.6 \times 10^{-10} cm^{-2}s^{-1}$ integrated in the 1-100 TeV energy range.

Authors:Stephen Kerby, Abraham D. Falcone, Paul S. Ray

Abstract: Following the discovery of radio pulsars at the position of Fermi-LAT unassociated sources by the TRAPUM group, we conduct Swift-XRT observations of six of those 4FGL sources to determine if any pulsar-like X-ray sources are present and to confirm the reported detection of an X-ray counterpart via eROSITA at 4FGL J1803.1-6708. At two of the six targets, we detect no X-ray sources at the TRAPUM radio position, placing an upper limit on the 0.3-10.0 keV flux. At 4FGL J1803.1-6708 we find an X-ray source at the TRAPUM and eROSITA position. At 4FGL J1858.3-5424 we find a new X-ray counterpart at the TRAPUM position with S/N=4.17, but also detect a distinct and separate X-ray source. At 4FGL J1823.8-3544 and 4FGL J1906.4-1757 we detect no X-ray flux at the TRAPUM positions, but we do detect separate X-ray sources elsewhere in the Fermi error ellipse. At these last two targets, our newly detected Swift sources are possible alternatives to the radio pulsar associations proposed by TRAPUM. Our findings confirm several of the discoveries reported by the TRAPUM group but suggest that further observations and investigations are necessary to confirm the low-energy counterpart of several unassociated sources.

Authors:Jiahui Huang, Hua Feng, Wei-Min Gu, Wen-Biao Wu

Abstract: We construct an analytical black hole accretion disk model that incorporates both magnetic pressure and disk wind, which are found to be important from numerical simulations. A saturated magnetic pressure that relates the Alfven velocity with local Keplerian velocity and gas sound speed is assumed in addition to radiation and gas pressures. The mass accretion rate is assumed to have a power-law form in response to mass loss in the wind. We find three sets of self-consistent solutions that are thermally stable and satisfy the model assumptions. At high accretion rates, the disk is geometrically and optically thick, resembling the slim disk solution. At relatively low accretion rates, our model predicts an accretion flow consisting of a geometrically thin and optically thick outer disk (similar to the standard disk), and a geometrically thick and optically thin inner disk (similar to the advection-dominated accretion flow or ADAF). Thus, this is a natural solution for a truncated disk connected with an inner ADAF, which has been proposed to explain some observations. The magnetic pressure plays a more important role than the outflow in shaping the disk structure. The observed disk luminosity tends to saturate around 8 times the Eddington limit, suggesting that supercritical accretion onto black holes can be used for black hole mass estimate, or a standard candle with known black hole masses.

Authors:Andrea Santangelo, Rosalia Madonia, Santina Piraino

Abstract: In this chapter, we briefly review the history of X-ray astronomy through its missions. We follow a temporal development, from the first instruments onboard rockets and balloons to the most recent and complex space missions. We intend to provide the reader with detailed information and references on the many missions and instruments that have contributed to the success of the exploration of the X-ray universe. We have not included missions that are still operating, providing the worldwide community with high-quality observations. Specific chapters for these missions are included in a dedicated section of the handbook.

Authors:O. C. Jones, P. J. Kavanagh, M. J. Barlow, T. Temim, C. Fransson, J. Larsson, J. A. D. L. Blommaert, M. Meixner, R. M. Lau, B. Sargent, P. Bouchet, J. Hjorth, G. S. Wright, A. Coulais, O. D. Fox, R. Gastaud, A. Glasse, N. Habel, A. S. Hirschauer, J. Jaspers, O. Krause, Lenkić, O. Nayak, A. Rest, T. Tikkanen, R. Wesson, L. Colina, E. F. van Dishoeck, M. Güdel, Th. Henning, P. -O. Lagage, Östlin, T. P. Ray, B. Vandenbussche

Abstract: Supernova (SN) 1987A is the nearest supernova in $\sim$400 years. Using the {\em JWST} MIRI Medium Resolution Spectrograph, we spatially resolved the ejecta, equatorial ring (ER) and outer rings in the mid-infrared 12,927 days after the explosion. The spectra are rich in line and dust continuum emission, both in the ejecta and the ring. Broad emission lines (280-380~km~s$^{-1}$ FWHM) seen from all singly-ionized species originate from the expanding ER, with properties consistent with dense post-shock cooling gas. Narrower emission lines (100-170~km~s$^{-1}$ FWHM) are seen from species originating from a more extended lower-density component whose high ionization may have been produced by shocks progressing through the ER, or by the UV radiation pulse associated with the original supernova event. The asymmetric east-west dust emission in the ER has continued to fade, with constant temperature, signifying a reduction in dust mass. Small grains in the ER are preferentially destroyed, with larger grains from the progenitor surviving the transition from SN into SNR. The ER is fit with a single set of optical constants, eliminating the need for a secondary featureless hot dust component. We find several broad ejecta emission lines from [Ne~{\sc ii}], [Ar~{\sc ii}], [Fe~{\sc ii}], and [Ni~{\sc ii}]. With the exception of [Fe~{\sc ii}]~25.99$\mu$m, these all originate from the ejecta close to the ring and are likely being excited by X-rays from the interaction. The [Fe~{\sc ii}]~5.34$\mu$m to 25.99$\mu$m line ratio indicates a temperature of only a few hundred K in the inner core, consistent with being powered by ${}^{44}$Ti decay.

Authors:Yoann Génolini, David Maurin, Igor V. Moskalenko, Michael Unger

Abstract: High-precision cosmic-ray data from ongoing and recent past experiments (Voyager, ACE-CRIS, PAMELA, ATIC, CREAM, NUCLEON, AMS-02, CALET, DAMPE) are being released in the tens of MeV/n to multi-TeV/n energy range. Astrophysical and dark matter interpretations of these data are limited by the precision of nuclear production cross-sections. In Paper I, PRC 98, 034611 (2018), we set up a procedure to rank nuclear reactions whose desired measurements will enable us to fully exploit currently available data on CR Li to N ($Z=3-7$) species. Here we extend these rankings to O up to Si nuclei ($Z=8-14$), also updating our results on the LiBeB species. We also highlight how comprehensive new high precision nuclear data, that could e.g. be obtained at the SPS at CERN, would be a game-changer for the determination of key astrophysical quantities (diffusion coefficient, halo size of the Galaxy) and indirect searches for dark matter signatures.

Authors:Jaume Zuriaga-Puig, Viviana Gammaldi, Daniele Gaggero, Thomas Lacroix, Miguel Ángel Sánchez-Conde

Abstract: We develop a comprehensive study of the gamma-ray flux observed by H.E.S.S. in 5 regions of the Galactic Center (GC). Motivated by previous works on a possible Dark Matter (DM) explanation for the TeV cut-off observed in the innermost $\sim 16$ pc of the Galaxy, we aim to constrain the DM density profile up to a radius $\sim 450$ pc from the GC. In this region, cosmological simulations and Galactic dynamics studies fail to produce a strong prediction of the DM profile. With our proof-of-concept analysis, we set upper limits on the density distribution of thermal multi-TeV WIMPs, compatible with the observed gamma-ray flux. The results agree with the hypothesis of a DM density enhancement in the GC with respect to the benchmark NFW profile ($\gamma=1$) and allow us to exclude profiles with a slope $\gamma \gtrsim 1.3$. We also investigate the possibility that such an enhancement could be related to the existence of a DM spike associated with the supermassive black hole Sgr A*. We find out that the existence of an adiabatic DM spike smoothed by the scattering off of WIMPs by the bulge stars may be consistent with the observed gamma-ray flux if the spike forms on an underlying generalized NFW profile with $\gamma \lesssim 0.8$, corresponding to a spike slope $\gamma_{sp-star}= 1.5$ and radius $R_\text{sp-stars} \sim 25$-$30$ pc. Instead, in the extreme case of the instantaneous growth of the black hole, the profile could have up to $\gamma \sim 1.2$, a corresponding $\gamma_{sp-inst}=1.4$ and $R_\text{sp-inst}\sim 15$-$25$ pc. Moreover, the results of our analysis of the total DM mass enclosed within the S2 orbit are less stringent than the spectral analysis. Our work aims to guide future studies of the GC region, with both current and next-generation telescopes, like the next Cherenkov Telescope Array, that will be able to scan the GC with improved flux sensitivity and angular resolution.

Authors:Thomas Celora

Abstract: This work is concerned with advancing multi-fluid models in General Relativity, and in particular focuses on the modelling of dissipative fluids and turbulent flows. Such models are required for an accurate description of neutron star phenomenology, and binary neutron star mergers in particular. In fact, the advent of multi-messenger astronomy offers exciting prospects for exploring the extreme physics at play during such cosmic fireworks. We first focus on modelling dissipative fluids in relativity, and explore the arguably unique model that is ideally suited for describing dissipative multi-fluids in General Relativity. Modelling single fluids in relativity is already a hard task, but for neutron stars it is easy to argue that we need to understand even more complicated settings: the presence of superfluid/superconducting mixtures, for example, means that we need to go beyond single-fluid descriptions. We then consider turbulent flows and focus on how to perform "filtering" in a curved spacetime setting. We do so as most recent turbulent models in a Newtonian setting are based on the notion of spatial filtering. As the same strategy is beginning to be applied in numerical relativity, we focus on the foundational underpinnings and propose a novel scheme for carrying out filtering, ensuring consistency with the tenets of General Relativity. Finally, we discuss two applications of relevance for binary neutron star mergers. We focus on the modelling of ($\beta$-)reactions in neutron star simulations, and provide a discussion of the magneto-rotational instability that is suited to highly dynamical environments like mergers. We focus on these two problems as reactions are expected to source the dominant dissipative contribution to the overall dynamics, while the magneto-rotational instability is considered crucial for sustaining the development of turbulence in mergers.

Authors:D. I. Palade

Abstract: A fast artificial neural network is developed for the prediction of cosmic ray transport in turbulent astrophysical magnetic fields. The setup is trained and tested on bespoke datasets that are constructed with the aid of test-particle numerical simulations of relativistic cosmic ray dynamics in synthetic stochastic fields. The neural network uses, as input, particle and field properties and estimates transport coefficients 10^7 faster than standard numerical simulations with an overall error of ~5% .

Authors:Takami Kuroda, Masaru Shibata

Abstract: We present an axisymmetric failed supernova simulation beyond black hole formation, for the first time with numerical relativity and two-moment multi energy neutrino transport. To ensure stable numerical evolution, we use an excision method for neutrino radiation-hydrodynamics within the inner part of black hole domain. We demonstrate that our excision method is capable to stably evolve the radiation-hydrodynamics in dynamical black hole spacetime. As a remarkable signature of the final moment of PNS, we find the emergence of high energy neutrinos. Those high energy neutrinos are associated with the proto-neutron star shock surface being swallowed by the central black hole and could be a possible observable of failed supernovae.

Authors:Jonas P. Pereira, Carlos H. Coimbra-Araújo, Rita C. dos Anjos, Jaziel G. Coelho

Abstract: Binary coalescences are known sources of gravitational waves (GWs) and they encompass combinations of black holes (BHs) and neutron stars (NSs). Here we show that when BHs are embedded in magnetic fields ($B$s) larger than approximately $10^{10}$ G, charged particles colliding around their event horizons can easily have center-of-mass energies in the range of ultra-high energies ($\gtrsim 10^{18}$ eV) and escape. Such B-embedding and high-energy particles can take place in BH-NS binaries, or even in BH-BH binaries with one of the BHs being charged (with charge-to-mass ratios as small as $10^{-5}$, which do not change GW waveforms) and having a residual accretion disk. Ultra-high center-of-mass energies for particle collisions arise for basically any rotation parameter of the BH when $B \gtrsim 10^{10}$ G, meaning that it should be a common aspect in binaries, especially in BH-NS ones given the natural presence of a $B$ onto the BH and charged particles due to the NS's magnetosphere. We estimate that up to millions of ultra-high center-of-mass collisions may happen before the merger of BH-BH and BH-NS binaries. Thus, binary coalescences can also be efficient sources of ultra-high energy cosmic rays (UHECRs) and constraints to NS/BH parameters would be possible if UHECRs are detected along with GWs.

Authors:Marco Turchetta, Manuel Linares, Karri Koljonen, Bidisha Sen

Abstract: We present the first multi-band optical light curves of PSR J1622-0315, among the most compact known redback binary millisecond pulsars, with an orbital period Porb=3.9 h. We find a flux modulation with two maxima per orbital cycle and a peak-to-peak amplitude of about 0.3 mag, which we attribute to the ellipsoidal shape of the tidally distorted companion star. The optical colours imply a late-F to early-G spectral type companion and do not show any detectable temperature changes along the orbit. This suggests that the irradiation of the star's inner face by the pulsar wind is unexpectedly missing despite its short orbital period. To interpret these results, we introduce a new parameter fsd, defined as the ratio between the pulsar wind flux intercepted by the companion star and the companion intrinsic flux. This flux ratio fsd, which depends on the spin-down luminosity of the pulsar, the base temperature of the companion and the orbital period, can be used to quantify the effect of the pulsar wind on the companion star and turns out to be the most important factor in determining whether the companion is irradiated or not. We find that the transition between these two regimes occurs at fsd=2-4 and that the value for PSR J1622-0315 is fsd=0.7, placing it firmly in the non-irradiated regime.

Authors:Shunhao Ji, Zhongxiang Wang, Yi Xing, Dahai Yan, Jintao Zheng

Abstract: Intrigued by recent high-energy study results for nearby galaxies with gamma-ray emission and in particular NGC~1068 that has been detected as a neutrino-emitting source by the IceCube Neutrino Observatory, we conduct detailed analysis of the $\gamma$-ray data for the galaxies NGC~1068 and NGC~253, obtained with the Large Area Telescope onboard {\it the Fermi Gamma-ray Space Telescope}. By checking for their possible spectral features and then constructing light curves in corresponding energy ranges, we identify flare-like activity from NGC ~1068 in $\geq$2\,GeV energy range and significant long-term variations of NGC~253 in $\geq$5\,GeV energy range. In the former, the emission appears harder in the two half-year flare-like events than that in the otherwise `quiescent' state. In the latter, there is a 2-times decrease in the flux before and after MJD~57023, which is clearly revealed by the test-statistic maps we obtain. Considering studies carried out and models proposed for the $\gamma$-ray emissions of the two sources, we discuss the implications of our findings. The jet in NGC~1068 may contribute to the \gr\ emission. The nature of the long-term variations in NGC~253 is not clear, but the variation part of the emission may be connected to the very-high-energy (VHE) emission of the galaxy and could be verified by VHE observations.

Authors:Sumedha Biswas, Zuzanna Kostrzewa-Rutkowska, Peter G. Jonker, Paul Vreeswijk, Deepak Eappachen, Paul J. Groot, Simon Hodgkin, Abdullah Yoldas, Guy Rixon, Diana Harrison, M. van Leeuwen, Dafydd Evans

Abstract: The discovery of gravitational wave (GW) events and the detection of electromagnetic counterparts from GW170817 has started the era of multimessenger GW astronomy.The field has been developing rapidly and in this paper,we discuss the preparation for detecting these events with the ESA Gaia satellite,during the 4th observing run of the LIGO-Virgo-KAGRA (LVK) collaboration that has started on May 24,2023. Gaia is contributing to the search for GW counterparts by a new transient detection pipeline called GaiaX. In GaiaX, a new source appearing in the field of view of only one of the two telescopes on-board Gaia is sufficient to send out an alert on the possible detection of a new transient. Ahead of O4, an experiment was conducted over a period of about two months. During the two weeks around New Moon in this period of time, the MeerLICHT (ML) telescope located in South Africa tried (weather permitting) to observe the same region of the sky as Gaia within 10 minutes. Any GaiaX detected transient was published publicly. ML and Gaia have similar limiting magnitudes for typical seeing conditions at ML. At the end of the experiment, we had 11861 GaiaX candidate transients and 15806 ML candidate transients, which we further analysed and the results of which are presented in this paper. Finally, we discuss the possibility and capabilities of Gaia contributing to the search for electromagnetic counterparts of gravitational wave events during O4 through the GaiaX detection and alert procedure.

Authors:Hsiu-Hsien Lin, Paul Scholz, Cherry Ng, Ue-Li Pen, Mohit Bhardwaj, Pragya Chawla, Alice P. Curtin, Ketan R. Sand, Shriharsh P. Tendulkar, Bridget Andersen, Kevin Bandura, Tomas Cassanelli, Amanda M. Cook, Matt Dobbs, Fengqiu Adam Dong, Gwendolyn Eadie, Emmanuel Fonseca, Bryan M. Gaensler, Utkarsh Giri, Antonio Herrera-Martin, Jane Kaczmarek, Joseph Kania, Victoria Kaspi, Kholoud Khairy, Adam E. Lanman, Calvin Leung, Dongzi Li, Kiyoshi W. Masui, Juan Mena-Parra, Bradley W. Meyers, Daniele Michilli, Nikola Milutinovic, Aaron B. Pearlman, Ziggy Pleunis, Masoud Rafiei-Ravandi, Mubdi Rahman, Pranav Sanghavi, Kaitlyn Shin, Kendrick Smith, Ingrid Stairs, David C. Stenning, Keith Vanderlinde, Dallas Wulf

Abstract: We report ten fast radio bursts (FRBs) detected in the far side-lobe region (i.e., $\geq 5^\circ$ off-meridian) of the Canadian Hydrogen Intensity Mapping Experiment (CHIME) from 2018 August 28 to 2021 August 31. We localize the bursts by fitting their spectra with a model of the CHIME/FRB synthesized beam response. CHIME/FRB did not observe repetition of similar brightness from the uniform sample of 10 side-lobe FRBs in a total exposure time of 35580 hours. Under the assumption of Poisson-distributed bursts, we infer that the mean repetition interval above the detecting threshold of the far side-lobe events is longer than 11880 hours, which is at least 2380 times larger than the interval from known CHIME/FRB detected repeating sources, with some caveats, notably that very narrow-band events could have been missed. Our results from these far side-lobe events suggest one of two scenarios: either (1) all FRBs repeat and the repetition intervals span a wide range, with high-rate repeaters being a rare subpopulation, or (2) non-repeating FRBs are a distinct population different from known repeaters.

Authors:Hsiu-Hsien Lin, Paul Scholz, Cherry Ng, Ue-Li Pen, D. Z. Li, Laura Newburgh, Alex Reda, Bridget Andersen, Kevin Bandura, Mohit Bhardwaj, Charanjot Brar, Tomas Cassanelli, Pragya Chawla, Amanda M. Cook, Alice P. Curtin, Matt Dobbs, Fengqiu Adam Dong, Emmanuel Fonseca, Bryan M. Gaensler, Utkarsh Giri, Alex S. Hill, Jane Kaczmarek, Joseph Kania, Victoria Kaspi, Kholoud Khairy, Calvin Leung, Kiyoshi W. Masui, Juan Mena-Parra, Bradley W. Meyers, Anna Ordog, Aaron B. Pearlman, Ziggy Pleunis, Masoud Rafiei-Ravandi, Mubdi Rahman, Scott Ransom, Ketan R. Sand, Pranav Sanghavi, Kaitlyn Shin, Kendrick Smith, Ingrid Stairs, Shriharsh P. Tendulkar, Keith Vanderlinde, Dallas Wulf

Abstract: We study the 10 fast radio bursts (FRBs) detected in the far side-lobe region of the CHIME telescope from 2018 August 28 to 2021 August 31. We find that the far side-lobe events have on average $\sim$500 times greater fluxes than events detected in CHIME's main lobe. We show that the side-lobe sample is therefore statistically $\sim$20 times closer than the main-lobe sample. The median dispersion measure (DM) excess, after removing the Galactic disk component using the NE2001 for the free electron density distribution of the Milky Way, of the 10 far side-lobe and 471 non-repeating main-lobe FRBs in the first CHIME/FRB catalog is 183.0 and 433.9 pc\;cm$^{-3}$, respectively. By comparing the DM excesses of the two populations under reasonable assumptions, we statistically constrain that the local degenerate contributions (from the Milky Way halo and the host galaxy) and the intergalactic contribution to the excess DM of the 471 non-repeating main-lobe FRBs for the NE2001 model are 131.2$-$158.3 and 302.7$-$275.6 pc cm$^{-3}$, respectively, which corresponds to a median redshift for the main-lobe FRB sample of $\sim$0.3. These constraints are useful for population studies of FRBs, and in particular for constraining the location of the missing baryons.

Authors:Daniel C. M. Palumbo, George N. Wong, Andrew A. Chael, Michael D. Johnson

Abstract: Images of supermassive black hole accretion flows contain features of both curved spacetime and plasma structure. Inferring properties of the spacetime from images requires modeling the plasma properties, and vice versa. The Event Horizon Telescope Collaboration has imaged near-horizon millimeter emission from both Messier 87* (M87*) and Sagittarius A* (Sgr A*) with very-long-baseline interferometry (VLBI) and has found a preference for magnetically arrested disk (MAD) accretion in each case. MAD accretion enables spacetime measurements through future observations of the photon ring, the image feature composed of near-orbiting photons. The ordered fields and relatively weak Faraday rotation of MADs yield rotationally symmetric polarization when viewed at modest inclination. In this letter, we utilize this symmetry along with parallel transport symmetries to construct a gain-robust interferometric quantity that detects the transition between the weakly lensed accretion flow image and the strongly lensed photon ring. We predict a shift in polarimetric phases on long baselines and demonstrate that the photon rings in M87* and Sgr A* can be unambiguously detected {with sensitive, long-baseline measurements. For M87* we find that photon ring detection in snapshot observations requires $\sim1$ mJy sensitivity on $>15$ G$\lambda$ baselines at 230 GHz and above, which could be achieved with space-VLBI or higher-frequency ground-based VLBI. For Sgr A*, we find that interstellar scattering inhibits photon ring detectability at 230 GHz, but $\sim10$ mJy sensitivity on $>12$ G$\lambda$ baselines at 345 GHz is sufficient, which is accessible from the ground. For both sources, these sensitivity requirements may be relaxed by repeated observations and averaging.

Authors:R. Abbasi, M. Ackermann, J. Adams, J. A. Aguilar, M. Ahlers, M. Ahrens, J. M. Alameddine, A. A. Alves Jr., N. M. Amin, K. Andeen, T. Anderson, G. Anton, C. Argüelles, Y. Ashida, S. Athanasiadou, S. Axani, X. Bai, A. Balagopal V., S. W. Barwick, V. Basu, S. Baur, R. Bay, J. J. Beatty, K. -H. Becker, J. Becker Tjus, J. Beise, C. Bellenghi, S. Benda, S. BenZvi, D. Berley, E. Bernardini, D. Z. Besson, G. Binder, D. Bindig, E. Blaufuss, S. Blot, M. Boddenberg, F. Bontempo, J. Y. Book, J. Borowka, S. Böser, O. Botner, J. Böttcher, E. Bourbeau, F. Bradascio, J. Braun, B. Brinson, S. Bron, J. Brostean-Kaiser, R. T. Burley, R. S. Busse, M. A. Campana, E. G. Carnie-Bronca, C. Chen, Z. Chen, D. Chirkin, K. Choi, B. A. Clark, K. Clark, L. Classen, A. Coleman, G. H. Collin, A. Connolly, J. M. Conrad, P. Coppin, P. Correa, D. F. Cowen, R. Cross, C. Dappen, P. Dave, C. De Clercq, J. J. DeLaunay, D. Delgado López, H. Dembinski, K. Deoskar, A. Desai, P. Desiati, K. D. de Vries, G. de Wasseige, T. DeYoung, A. Diaz, J. C. Díaz-Vélez, M. Dittmer, H. Dujmovic, M. Dunkman, M. A. DuVernois, T. Ehrhardt, P. Eller, R. Engel, H. Erpenbeck, J. Evans, P. A. Evenson, K. L. Fan, A. R. Fazely, A. Fedynitch, N. Feigl, S. Fiedlschuster, A. T. Fienberg, C. Finley, L. Fischer, D. Fox, A. Franckowiak, E. Friedman, A. Fritz, P. Fürst, T. K. Gaisser, J. Gallagher, E. Ganster, A. Garcia, S. Garrappa, L. Gerhardt, A. Ghadimi, C. Glaser, T. Glauch, T. Glüsenkamp, N. Goehlke, A. Goldschmidt, J. G. Gonzalez, S. Goswami, D. Grant, T. Grégoire, S. Griswold, C. Günther, P. Gutjahr, C. Haack, A. Hallgren, R. Halliday, L. Halve, F. Halzen, M. Ha Minh, K. Hanson, J. Hardin, A. A. Harnisch, A. Haungs, K. Helbing, F. Henningsen, E. C. Hettinger, S. Hickford, J. Hignight, C. Hill, G. C. Hill, K. D. Hoffman, K. Hoshina, W. Hou, F. Huang, M. Huber, T. Huber, K. Hultqvist, M. Hünnefeld, R. Hussain, K. Hymon, S. In, N. Iovine, A. Ishihara, M. Jansson, G. S. Japaridze, M. Jeong, M. Jin, B. J. P. Jones, D. Kang, W. Kang, X. Kang, A. Kappes, D. Kappesser, L. Kardum, T. Karg, M. Karl, A. Karle, U. Katz, M. Kauer, M. Kellermann, J. L. Kelley, A. Kheirandish, K. Kin, J. Kiryluk, S. R. Klein, A. Kochocki, R. Koirala, H. Kolanoski, T. Kontrimas, L. Köpke, C. Kopper, S. Kopper, D. J. Koskinen, P. Koundal, M. Kovacevich, M. Kowalski, T. Kozynets, E. Krupczak, E. Kun, N. Kurahashi, N. Lad, C. Lagunas Gualda, J. L. Lanfranchi, M. J. Larson, F. Lauber, J. P. Lazar, J. W. Lee, K. Leonard, A. Leszczyńska, Y. Li, M. Lincetto, Q. R. Liu, M. Liubarska, E. Lohfink, C. J. Lozano Mariscal, L. Lu, F. Lucarelli, A. Ludwig, W. Luszczak, Y. Lyu, W. Y. Ma, J. Madsen, K. B. M. Mahn, Y. Makino, S. Mancina, I. C. Mariş, I. Martinez-Soler, R. Maruyama, S. McCarthy, T. McElroy, F. McNally, J. V. Mead, K. Meagher, S. Mechbal, A. Medina, M. Meier, S. Meighen-Berger, Y. Merckx, J. Micallef, D. Mockler, T. Montaruli, R. W. Moore, K. Morik, R. Morse, M. Moulai, T. Mukherjee, R. Naab, R. Nagai, R. Nahnhauer, U. Naumann, J. Necker, L. V. Nguyen, H. Niederhausen, M. U. Nisa, S. C. Nowicki, D. Nygren, A. Obertacke Pollmann, M. Oehler, B. Oeyen, A. Olivas, E. O'Sullivan, H. Pandya, D. V. Pankova, N. Park, G. K. Parker, E. N. Paudel, L. Paul, C. Pérez de los Heros, L. Peters, J. Peterson, S. Philippen, S. Pieper, A. Pizzuto, M. Plum, Y. Popovych, A. Porcelli, M. Prado Rodriguez, B. Pries, G. T. Przybylski, C. Raab, J. Rack-Helleis, A. Raissi, M. Rameez, K. Rawlins, I. C. Rea, Z. Rechav, A. Rehman, P. Reichherzer, R. Reimann, G. Renzi, E. Resconi, S. Reusch, W. Rhode, M. Richman, B. Riedel, E. J. Roberts, S. Robertson, G. Roellinghoff, M. Rongen, C. Rott, T. Ruhe, D. Ryckbosch, D. Rysewyk Cantu, I. Safa, J. Saffer, D. Salazar-Gallegos, P. Sampathkumar, S. E. Sanchez Herrera, A. Sandrock, M. Santander, S. Sarkar, S. Sarkar, K. Satalecka, M. Schaufel, H. Schieler, S. Schindler, T. Schmidt, A. Schneider, J. Schneider, F. G. Schröder, L. Schumacher, G. Schwefer, S. Sclafani, D. Seckel, S. Seunarine, A. Sharma, S. Shefali, N. Shimizu, M. Silva, B. Skrzypek, B. Smithers, R. Snihur, J. Soedingrekso, A. Sogaard, D. Soldin, C. Spannfellner, G. M. Spiczak, C. Spiering, M. Stamatikos, T. Stanev, R. Stein, J. Stettner, T. Stezelberger, B. Stokstad, T. Stürwald, T. Stuttard, G. W. Sullivan, I. Taboada, S. Ter-Antonyan, J. Thwaites, S. Tilav, F. Tischbein, K. Tollefson, C. Tönnis, S. Toscano, D. Tosi, A. Trettin, M. Tselengidou, C. F. Tung, A. Turcati, R. Turcotte, C. F. Turley, J. P. Twagirayezu, B. Ty, M. A. Unland Elorrieta, N. Valtonen-Mattila, J. Vandenbroucke, N. van Eijndhoven, D. Vannerom, J. van Santen, J. Veitch-Michaelis, S. Verpoest, C. Walck, W. Wang, T. B. Watson, C. Weaver, P. Weigel, A. Weindl, M. J. Weiss, J. Weldert, C. Wendt, J. Werthebach, M. Weyrauch, N. Whitehorn, C. H. Wiebusch, N. Willey, D. R. Williams, M. Wolf, G. Wrede, J. Wulff, X. W. Xu, J. P. Yanez, E. Yildizci, S. Yoshida, S. Yu, T. Yuan, Z. Zhang, P. Zhelnin

Abstract: The origin of high-energy cosmic rays, atomic nuclei that continuously impact Earth's atmosphere, has been a mystery for over a century. Due to deflection in interstellar magnetic fields, cosmic rays from the Milky Way arrive at Earth from random directions. However, near their sources and during propagation, cosmic rays interact with matter and produce high-energy neutrinos. We search for neutrino emission using machine learning techniques applied to ten years of data from the IceCube Neutrino Observatory. We identify neutrino emission from the Galactic plane at the 4.5$\sigma$ level of significance, by comparing diffuse emission models to a background-only hypothesis. The signal is consistent with modeled diffuse emission from the Galactic plane, but could also arise from a population of unresolved point sources.

Authors:Sujoy Kumar Nath, Dipak Debnath, Kaushik Chatterjee, Riya Bhowmick, Hsiang-Kuang Chang, Sandip K. Chakrabarti

Abstract: We study the recent outburst of the black hole candidate EXO 1846-031 which went into an outburst in 2019 after almost 34 years in quiescence. We use archival data from Swift/XRT, MAXI/GSC, NICER/XTI and NuSTAR/FPM satellites/instruments to study the evolution of the spectral and temporal properties of the source during the outburst. Low energy X-ray flux of the outburst shows multiple peaks making it a multipeak outburst. Evolving type-C quasi-periodic oscillations (QPOs) are observed in the NICER data in the hard, hard intermediate and soft intermediate states. We use the physical Two Component Advective Flow (TCAF) model to analyze the combined spectra of multiple satellite instruments. According to the TCAF model, the accreting matter is divided into Keplerian and sub-Keplerian parts, and the variation in the observed spectra in different spectral states arises out of the variable contributions of these two types of accreting matter in the total accretion rate. Studying the evolution of the accretion rates and other properties of the accretion flow obtained from the spectral analysis, we show how the multiple peaks in the outburst flux arises out of discontinuous supply and different radial velocities of two types of accreting matter from the pile-up radius. We detect an Fe emission line at $\sim6.6$ keV in the hard and the intermediate states in the NICER spectra. We determine the probable mass of the black hole to be $12.43^{+0.14}_{-0.03}~M_\odot$ from the spectral analysis with the TCAF model. We also estimate viscous time scale of the source in this outburst to be $\sim 8$ days from the peak difference of the Keplerian and sub-Keplerian mass accretion rates.

Authors:Angelo Ricarte, Ramesh Narayan, Brandon Curd

Abstract: A spinning black hole accreting from a disk of strongly magnetized plasma via a magnetically arrested disk is known to produce an efficient electromagnetic jet powered by the black hole's spin energy. We present general relativistic radiative magnetohydrodynamic simulations of magnetically arrested systems covering a range of sub- to super-Eddington accretion rates. Using the numerical results from these simulation, we develop formulae to describe the magnetization, jet efficiency, and spin evolution of an accreting black hole as a function of its spin and accretion rate. A black hole with near-Eddington accretion experiences a mild degree of spin-down because of angular momentum loss through the jet, leading to an equilibrium spin of 0.8 rather than 1.0 at the Eddington limit. As the accretion rate increases above Eddington, the spin-down effect becomes progressively stronger, ultimately converging on previous predictions based on non-radiative simulations. In particular, spin evolution drives highly super-Eddington systems toward a black hole spin near zero. The formulae developed in this letter may be applied to galaxy and cosmological scale simulations that include black holes. If magnetically arrested disk accretion is common among supermassive black holes, the present results have broad implications for active galactic nucleus feedback and cosmological spin evolution.

Authors:Ruchika Dhaka, Ranjeev Misra, JS Yadav, Pankaj Jain

Abstract: In this work, we study the correlation between Quasi-periodic Oscillation (QPO) frequency and the spectral parameters during various X-ray states in the black hole binary GRS 1915+105 which matches well with the predicted relativistic dynamic frequency (i.e. the inverse of the sound crossing time) at the truncated radii. We have used broadband data of LAXPC and SXT instruments onboard AstroSat. Spectral fitting shows that the accretion rate varies from $\sim 0.1$ to $\sim 5.0 \times 10^{18}$ gm/s and the truncated radius changing from the last stable orbit of an almost maximally spinning black hole, $\sim$ 1.2 to $\sim$ 19 Gravitational radii. For this wide range, the frequencies of the C-type QPO (2 - 6 Hz) follow the trend predicted by the relativistic dynamical frequency model and interestingly, the high-frequency QPO at $\sim$ 70 Hz also follows the same trend, suggesting they originate from the innermost stable circular orbit with the same mechanism as the more commonly observed C-type QPO. While the qualitative trend is as predicted, there are quantitative deviations between the data and the theory, and the possible reasons for these deviations are discussed.

Authors:Sai Wang, Zhi-Chao Zhao

Abstract: Strong evidence for the Helling-Downs correlations have been reported by several pulsar timing array collaborations in middle 2023. In this work, we study the state-of-the-art graviton mass bounds by analyzing the observational data of overlap ruduction functions from NANOGrav 15-year data release and CPTA first data release. The data analysis places upper limits on the graviton mass at 95\% confidence level, namely, $m_{g}\lesssim0.43\times10^{-23}\mathrm{eV}$ for NANOGrav and $m_{g}\lesssim0.57\times10^{-23}\mathrm{eV}$ for CPTA. In addition, we discuss implications of these results for scenarios of ultralight tensor dark matter.

Authors:Lilly Pyras, Christian Glaser, Steffen Hallmann, Anna Nelles

Abstract: Experiments seeking to detect radio emission stemming from neutrino interactions will soon reach sensitivities that bring a detection within reach. Since experiments like RNO-G or the future IceCube-Gen2 target more than an order of magnitude more effective volume than existing experiments, the renewed and detailed study of rare backgrounds is needed. In this paper, we study the potential background from energy losses of highly energetic atmospheric muons. Due to both limited experimental measurements and limited modeling in hadronic interaction models, the expected event rate is subject to large uncertainties. Here, we estimate rate predictions and their uncertainties for different models and instrumental parameters. We also study possible routes towards mitigation, such as parent air shower detection, and illustrate what is needed to make the first measurement of the prompt muon flux at energies above 10 PeV.

Authors:Nicole R. Crumpler William H. Miller III Department of Physics and Astronomy, Johns Hopkins University Baltimore, MD USA

Abstract: We constrain a broad class of "hairy" black hole models capable of directly sourcing electromagnetic radiation during a binary black hole merger. This signal is generic and model-independent since it is characterized by the black hole mass ($M$) and the fraction of that mass released as radiation ($\epsilon$). For field energy densities surpassing the Schwinger limit, this mechanism triggers pair-production to produce a gamma-ray burst. By cross-referencing gravitational wave events with gamma-ray observations, we place upper bounds of $\epsilon<10^{-5}-10^{-4}$ for $10-50$ $M_\odot$ black holes depending on the black hole mass. We discuss the weak detection of a gamma-ray burst following GW150914 and show that this event is consistent with rapid electromagnetic emission directly from a "hairy" black hole with $\epsilon\sim10^{-7}-10^{-6}$. Below the Schwinger limit, ambient charged particles are rapidly accelerated to nearly the speed of light by the strong electromagnetic field. For 1-50 $M_\odot$ black holes and $\epsilon$ ranging from $10^{-20}$ to $10^{-7}$, the typical proton energies are $\sim20$ GeV-20 TeV and electron energies are $\sim0.01-10$ GeV. At these energies, cosmic ray protons and electrons quickly diffuse into the Milky Way's background magnetic field, making it difficult to identify a point source producing them. Overall, constraining $\epsilon$ in this less energetic regime becomes difficult and future constraints may need to consider specific models of "hairy" black holes.

Authors:C. J. Law Caltech, Owens Valley Radio Observatory, K. Sharma Caltech, Owens Valley Radio Observatory, V. Ravi Caltech, Owens Valley Radio Observatory, G. Chen Caltech, Owens Valley Radio Observatory, M. Catha Caltech, Owens Valley Radio Observatory, L. Connor Caltech, Owens Valley Radio Observatory, J. T. Faber Caltech, Owens Valley Radio Observatory, G. Hallinan Caltech, Owens Valley Radio Observatory, C. Harnach Caltech, Owens Valley Radio Observatory, G. Hellbourg Caltech, Owens Valley Radio Observatory, R. Hobbs Caltech, Owens Valley Radio Observatory, D. Hodge Caltech, Owens Valley Radio Observatory, M. Hodges Caltech, Owens Valley Radio Observatory, J. W. Lamb Caltech, Owens Valley Radio Observatory, P. Rasmussen Caltech, Owens Valley Radio Observatory, M. B. Sherman Caltech, Owens Valley Radio Observatory, J. Shi Caltech, Owens Valley Radio Observatory, D. Simard Caltech, Owens Valley Radio Observatory, R. Squillace Caltech, Owens Valley Radio Observatory, S. Weinreb Caltech, Owens Valley Radio Observatory, D. P. Woody Caltech, Owens Valley Radio Observatory, N. Yadlapalli Caltech, Owens Valley Radio Observatory

Abstract: Fast Radio Bursts (FRBs) are a powerful and mysterious new class of transient that are luminous enough to be detected at cosmological distances. By associating FRBs to host galaxies, we can measure intrinsic and environmental properties that test FRB origin models, in addition to using them as precise probes of distant cosmic gas. The 110-antenna Deep Synoptic Array (DSA-110) is a radio interferometer built to maximize the rate at which it can simultaneously detect and localize FRBs. Here, we present the first sample of FRBs and host galaxies discovered by the DSA-110. This sample of 11 FRBs is the largest uniform sample of localized FRBs to date and is selected based on association to host galaxies identified in optical imaging by Pan-STARRS1 and follow-up spectroscopy at the Palomar and Keck observatories. These FRBs have not been observed to repeat and their radio properties (dispersion, temporal scattering, energy) are similar to that of the known non-repeating FRB population. Most host galaxies have ongoing star formation, as has been identified before for FRB hosts. In contrast to prior work, a large fraction (four of eleven) of the new sample are more massive than 10$^{11}$\ M$_{\odot}$ and most had elevated star formation rates more than 100 Myr in their past. The distribution of star-formation history across this host-galaxy sample shows that the delay-time distribution is wide, spanning from $\sim100$\,Myr to $\sim10$\,Gyr. This requires the existence of one or more progenitor formation channels associated with old stellar populations, such as the binary evolution of compact objects.

Authors:Qian-Qian Zhang, Ping Zhou, Yang Chen, Xiao Zhang, Wen-Juan Zhong, Xin Zhou, Zhi-Yu Zhang, Jacco Vink

Abstract: Galactic supernova remnants (SNRs) play an important role in our understanding of supernovae and their feedback on the interstellar environment. SNR G352.7$-$0.1 is special for its thermal composite morphology and double-ring structure. We have performed spectroscopic mapping in $^{12}$CO and $^{13}$CO $J=2$-1 lines toward G352.7$-$0.1 with the Atacama Pathfinder Experiment telescope. Broad $^{12}$CO lines are found in the northeastern ring at a local-standard-of-rest velocity range of $\sim-50$-$-30$ km s$^{-1}$, suggesting that the remnant is interacting with molecular clouds (MCs) at $\sim-51$ km s$^{-1}$. Thus, we adopt a distance of $\sim10.5$ kpc for this SNR. The momentum and kinetic energy of the shocked gas along the line of sight are estimated to be $\sim10^2{\rm M_{sun}}$ km s$^{-1}$ and $\sim10^{46}$ erg, respectively. We also find an expanding structure around the remnant, which is possibly related to the wind-blown bubble of the progenitor star. From the Fermi-LAT data in an energy range of 0.1-500 GeV, we find no gamma-ray counterparts of G352.7$-$0.1.

Authors:Hao Ma, Youjun Lu, Xiao Guo, Siqi Zhang, Qingbo Chu

Abstract: Future ground-based gravitational wave (GW) detectors, i.e., Einstein telescope (ET) and Cosmic Explorer (CE), are expected to detect a significant number of lensed binary neutron star (BNS) mergers, which may provide a unique tool to probe cosmology. In this paper, we investigate the detectability of the optical/infrared electromagnetic (EM) counterparts (kilonovae/afterglows) from these lensed BNS mergers by future GW detectors and EM telescopes using simple kilonova, afterglow, and lens models. ET and CE are expected to detect $\sim5.32^{+26.1}_{-5.10}$ and $67.3^{+332}_{-64.7}$ lensed BNS mergers per year. We find that the EM counterparts associated with all these mergers will be detectable by an all sky-survey in the H-band with the limiting magnitude $m_{\textrm{lim}}\gtrsim27$, while the detectable fraction is $\lesssim0.4\%$ in the g-/z-band if with $m_{\textrm{lim}}\lesssim24$. Generally it is more efficient to search the lensed EM counterparts by adopting the infrared bands than the optical/UV bands with the same $m_{\textrm{lim}}$. Future telescopes like Vera C. Rubin Observatory, China Space Station Telescope, and Euclid can hardly detect the EM counterparts of even one lensed BNS merger. Roman Space Telescope (RST) and James Webb Space Telescope (JWST) have the capability to detect about a few or more such events per year. Moreover, the time delays and separations between the lensed image pairs are typically in the ranges from minutes to months and from $0.1$ to $1$\,arcsec, suggesting that both the GW and EM images of most lensed BNS mergers can be well resolved by not only CE/ET in the time domain but also RST/JWST spatially.

Authors:Chen Yaling, Feng Zhang, Hu Liu, Fengrong Zhu

Abstract: The knee of cosmic ray spectra reflects the maximum energy accelerated by galactic cosmic ray sources or the limit to the ability of galaxy to bind cosmic rays. The measuring of individual energy spectra is a crucial tool to ascertain the origin of the knee. The Extensive Air Shower of cosmic rays in the knee energy region is simulated via CORSIKA software. The energy resolution for different secondary components and primary nuclei identification capability are studied. The energy reconstruction by using electromagnetic particles in the energy around knee is better than by using other secondary particles. The resolution is 10-19 percent for proton, and 4-8 percent for iron. For the case of primary nuclei identification capability, the discriminability of density of muons is best both at low (around 100 TeV) and high (around 10 PeV) energy, the discriminability of the shape of lateral distribution of electron and gamma-rays are good at low energy and the discriminability of density of neutrons is good at high energy. The differences between the lateral distributions of secondary particles simulated by EPOS-LHC and QGSJet-II-04 hadronic model are also studied. The results in this work can provide important information for selecting the secondary components and detector type during energy reconstruction and identifying the primary nuclei of cosmic rays in the knee region.

Authors:Ian Heywood

Abstract: MeerKAT imaging of the globular cluster 47 Tucanae (47 Tuc) reveals 1.28 GHz continuum emission at the locations of 20 known millisecond pulsars (MSPs). We use time series and spectral imaging to investigate the image-domain characteristics of the MSPs, and search for previously unknown sources of interest. The MSPs exhibit a range of differences in their temporal and spectral properties compared the general background radio source population. Temporal variability differs strongly from pulsar to pulsar, some appearing to vary randomly on 15 min timescales, others varying coherently by factors of >10 on timescales of hours. The error in the typical power law fit to the spectrum emerges as a powerful parameter for indentifying the MSPs. This behaviour is likely due to differing diffractive scintillation conditions along the sight lines to the MSPs. One MSP exhibits tentative periodic variations that are consistent with modulation due the orbit of an eclipsing binary system. One radio source has spectro-temporal properites closely resembling those of the MSP population in the cluster, and we report its position as a candidate new MSP, or alternatively an interferometric localisation of one of six MSPs which do not yet have an accurate position from the timing solutions.

Authors:A. Levan, B. P. Gompertz, O. S. Salafia, M. Bulla, E. Burns, K. Hotokezaka, L. Izzo, G. P. Lamb, D. B. Malesani, S. R. Oates, M. E. Ravasio, A. Rouco Escorial, B. Schneider, N. Sarin, S. Schulze, N. R. Tanvir, K. Ackley, G. Anderson, G. B. Brammer, L. Christensen, V. S. Dhillon, P. A. Evans, M. Fausnaugh, W. -F. Fong, A. S. Fruchter, C. Fryer, J. P. U. Fynbo, N. Gaspari, K. E. Heintz, J. Hjorth, J. A. Kennea, M. R. Kennedy, T. Laskar, G. Leloudas, I. Mandel, A. Martin-Carrillo, B. D. Metzger, M. Nicholl, A. Nugent, J. T. Palmerio, G. Pugliese, J. Rastinejad, L. Rhodes, A. Rossi, S. J. Smartt, H. F. Stevance, A. Tohuvavohu, A. van der Horst, S. D. Vergani, D. Watson, T. Barclay, K. Bhirombhakdi, E. Breedt, A. A. Breeveld, A. J. Brown, S. Campana, A. A. Chrimes, P. D'Avanzo, V. D'Elia, M. De Pasquale, M. J. Dyer, D. K. Galloway, J. A. Garbutt, M. J. Green, D. H. Hartmann, P. Jakobsson, P. Kerry, D. Langeroodi, J. K. Leung, S. P. Littlefair, J. Munday, P. O'Brien, S. G. Parsons, I. Pelisoli, A. Saccardi, D. I. Sahman, R. Salvaterra, B. Sbarufatti, D. Steeghs, G. Tagliaferri, C. C. Thöne, A. de Ugarte Postigo, D. A. Kann

Abstract: The mergers of binary compact objects such as neutron stars and black holes are of central interest to several areas of astrophysics, including as the progenitors of gamma-ray bursts (GRBs), sources of high-frequency gravitational waves and likely production sites for heavy element nucleosynthesis via rapid neutron capture (the r-process). These heavy elements include some of great geophysical, biological and cultural importance, such as thorium, iodine and gold. Here we present observations of the exceptionally bright gamma-ray burst GRB 230307A. We show that GRB 230307A belongs to the class of long-duration gamma-ray bursts associated with compact object mergers, and contains a kilonova similar to AT2017gfo, associated with the gravitational-wave merger GW170817. We obtained James Webb Space Telescope mid-infrared (mid-IR) imaging and spectroscopy 29 and 61 days after the burst. The spectroscopy shows an emission line at 2.15 microns which we interpret as tellurium (atomic mass A=130), and a very red source, emitting most of its light in the mid-IR due to the production of lanthanides. These observations demonstrate that nucleosynthesis in GRBs can create r-process elements across a broad atomic mass range and play a central role in heavy element nucleosynthesis across the Universe.

Authors:Zhi-Lin Chen, Rui-Chong Hu, Da-Bin Lin, En-Wei Liang

Abstract: It is proposed that one-off fast radio burst (FRB) with periodic structures may be produced during the inspiral phase of a binary neutron-star (BNS) merger. In this paper, we study the event rate of such kind of FRB. We first investigate the properties of two one-off FRBs with periodic structures (i.e., FRB~20191221A and FRB~20210213A) in this scenario, by assuming the fast magnetosonic wave is responsible for their radio emission. For the luminosities and periods of these bursts, it is found that the pre-merger BNS with magnetic field strength $B\gtrsim 10^{12}\,{\rm Gs}$ is required. This is relatively high compared with that of the most of the BNSs observed in our Galaxy, of which the magnetic field is around $10^{9}\,{\rm Gs}$. Since the observed BNSs in our Galaxy are the binaries without suffering merger, a credited event rate of BNS-merger originated FRBs should be estimated by considering the evolution of both the BNS systems and their magnetic fields. Based on the population synthesis and adopting a decaying magnetic field of NSs, we estimate the event rate of BNS-mergers relative to their final magnetic fields. We find that the rapid merged BNSs tend to merge with high magnetization, and the event rate of BNS-merger originated FRBs, i.e., the BNS-mergers with both NSs' magnetic field being higher than $10^{12}\,{\rm Gs}$ is $\sim8\times10^{4}\,\rm{yr}^{-1}$ ($19 \%$ of the total BNS-mergers) in redshift $z<1$.

Authors:Dong Zheng, Zhongxiang Wang, Yi Xing

Abstract: PSR~J0631+1036 is a middle-aged pulsar with properties similar to those of the nearby Geminga pulsar. It is bright in $\gamma$-rays, and has been noted as the only source possibly associated with the TeV source 3HWC J0631+107 (also the LHAASO J0631+1040). For understanding the nature of the TeV source, we analyze the GeV $\gamma$-ray data obtained with the Large Area Telescope (LAT) onboard {\it the Fermi Gamma-ray Space Telescope} for the source region. We are able to remove the pulsar's emission from the region from timing analysis, and find that the region is rather clean without possible GeV $\gamma$-ray emission present as the counterpart to the TeV source. By comparing this pulsar to Geminga and considering the spectral feature of the TeV source, we argue that it is likely the TeV halo powered by the pulsar.

Authors:Maokai Hu, Lifan Wang, Xiaofeng Wang, Lingzhi Wang

Abstract: Type Ia supernovae (SNe Ia) arise from the thermonuclear explosion in binary systems involving carbon-oxygen white dwarfs (WDs). The pathway of WDs acquiring mass may produce circumstellar material (CSM). Observing SNe Ia within a few hours to a few days after the explosion can provide insight into the nature of CSM relating to the progenitor systems. In this paper, we propose a CSM model to investigate the effect of ejecta-CSM interaction on the early-time multi-band light curves of SNe Ia. By varying the mass-loss history of the progenitor system, we apply the ejecta-CSM interaction model to fit the optical and ultraviolet (UV) photometric data of eight SNe Ia with early excess. The photometric data of SNe Ia in our sample can be well-matched by our CSM model except for the UV-band light curve of iPTF14atg, indicating its early excess may not be due to the ejecta-CSM interaction. Meanwhile, the CSM interaction can generate synchrotron radiation from relativistic electrons in the shocked gas, making radio observations a distinctive probe of CSM. The radio luminosity based on our models suggests that positive detection of the radio signal is only possible within a few days after the explosion at higher radio frequencies (e.g., ~250 GHz); at lower frequencies (e.g., ~1.5 GHz) the detection is difficult. These models lead us to conclude that a multi-messenger approach that involves UV, optical, and radio observations of SNe Ia a few days past explosion is needed to address many of the outstanding questions concerning the progenitor systems of SNe Ia.

Authors:Yu-Bin Wang, Abdusattar Kurban, Xia Zhou, Yun-Wei Yu, Na Wang

Abstract: FRB 180916.J0158+65 is a well-known repeating fast radio burst with a period ($16.35~\rm days$) and an active window ($5.0~\rm days$). We give out the statistical results of the dispersion measures and waiting times of bursts of FRB 180916.J0158+65. We find the dispersion measures at the different frequencies show a bimodal distribution. The peaking dispersion measures of the left mode of the bimodal distributions increase with frequency, but the right one is inverse. The waiting times also present the bimodal distribution, peaking at 0.05622s and 1612.91266s. The peaking time is irrelevant to the properties of bursts, either for the preceding or subsequent burst. By comparing the statistical results with possible theoretical models, we suggest that FRB 180916.J0158+65 suffered from the plasma lensing effects in the propagation path. Moreover, this source may be originated from a highly magnetized neutron star in a high-mass X-ray binary.

Authors:Y. Y. Kovalev, A. V. Plavin, A. B. Pushkarev, S. V. Troitsky

Abstract: The advancement of neutrino observatories has sparked a surge in multi-messenger astronomy. Multiple neutrino associations among blazars are reported while neutrino production site is located within their central (sub)parsecs. Yet many questions remain on the nature of those processes. The next generation Event Horizon Telescope (ngEHT) is uniquely positioned for these studies, as its high frequency and resolution can probe both the accretion disk region and the parsec-scale jet. This opens up new opportunities for connecting the two regions and unraveling the proton acceleration and neutrino production in blazars. We outline observational strategies for ngEHT and highlight what it can contribute to the multi-messenger study of blazars.

Authors:Vibhavasu Pasumarti, Shantanu Desai

Abstract: We use the spectral lag data of 32 long GRBs detected by Fermi/GBM, which has been recently collated in Liu et al (2022) to carry out a search for Lorentz Invariance violation (LIV) using Bayesian model selection. We use two different parametric functions to model the null hypothesis of only intrinsic emission: a smooth broken power law model (SBPL) (proposed in Liu et al) as well as a simple power law model, which has been widely used before in literature. We find that using the SBPL model as the null hypothesis, only three GRBs show decisive evidence for linear LIV, of which only one shows decisive evidence for quadratic LIV. When we use the simple power-law model as the null hypothesis, we find 15 and 16 GRBs showing decisive evidence for linear and quadratic LIV, respectively. Finally, when we apply the SBPL model to model the intrinsic emission in GRB 1606025B, the evidence for LIV (which was previously reported using the simple power law model) disappears. This underscores the importance of adequately modelling the intrinsic emission while searching for evidence of LIV using spectral lags.

Authors:M. P. Snelders, K. Nimmo, J. W. T. Hessels, Z. Bensellam, L. P. Zwaan, P. Chawla, O. S. Ould-Boukattine, F. Kirsten, J. T. Faber, V. Gajjar

Abstract: Fast radio bursts (FRBs) are extragalactic transients with typical durations of milliseconds. FRBs have been shown, however, to fluctuate on a wide range of timescales: some show sub-microsecond sub-bursts while others last up to a few seconds in total. Probing FRBs on a range of timescales is crucial for understanding their emission physics, how to detect them effectively, and how to maximize their utility as astrophysical probes FRB 20121102A is the first-known repeating FRB source. Here we show that FRB 20121102A is able to produce isolated microsecond-duration bursts whose total durations are more than ten times shorter than all other known FRBs. The polarimetric properties of these micro-bursts resemble those of the longer-lasting bursts, suggesting a common emission mechanism producing FRBs spanning a factor of 1,000 in duration. Furthermore, this work shows that there exists a population of ultra-fast radio bursts that current wide-field FRB searches are missing due to insufficient time-resolution.

Authors:Marco Ajello, Kohta Murase, Alex McDaniel

Abstract: The recent detection of high-energy neutrinos by IceCube in the direction of the nearby Seyfert/starburst galaxy NGC 1068 implies that radio-quiet active galactic nuclei can accelerate cosmic-ray ions. Dedicated multi-messenger analyses suggest that the interaction of these high-energy ions { with ambient gas or photons} happens in a region of the galaxy that is highly opaque for GeV-TeV gamma rays. Otherwise, the GeV-TeV emission would violate existing constraints provided by {\it Fermi}-LAT and MAGIC. The conditions of high optical depth are realized near the central super-massive black hole (SMBH). At the same time, the GeV emission detected by the {\it Fermi}-Large Area Telescope (LAT) is likely related to the galaxy's sustained star-formation activity. In this work, we derive a 20\,MeV - 1\,TeV spectrum of NGC 1068 using 14\,yrs of {\it Fermi}-LAT observations. We find that the starburst hadronic component is responsible for NGC 1068's emission above $\sim$500\,MeV. However, below this energy an additional component is required. In the 20-500\,MeV range the {\it Fermi}-LAT data are consistent with hadronic emission {initiated by non-thermal ions interacting with gas or photons} in the vicinity of the central SMBH. This highlights the importance of the MeV band to discover hidden cosmic-ray accelerators.

Authors:Deepika Venkattu, Peter Lundqvist, Miguel Pérez-Torres, Leah Morabito, Javier Moldón, John Conway, Poonam Chandra, Cyril Tasse

Abstract: We present an International LOFAR Telescope sub-arcsecond resolution image of the nearby galaxy M 51 with a beam size of 0.436" x 0.366" and rms of 46 $\mu$Jy. We compare this image with an European VLBI Network study of M 51, and discuss the supernovae in this galaxy, which have not yet been probed at these low radio frequencies. We find a flux density of 0.97 mJy for SN 2011dh in the ILT image, which is about five times smaller than the flux density reported by the LOFAR Twometre Sky Survey at 6" resolution using the same dataset without the international stations. This difference makes evident the need for LOFAR international baselines to reliably obtain flux density measurements of compact objects in nearby galaxies. Our LOFAR flux density measurement of SN 2011dh directly translates into fitting the radio light curves for the supernova and constraining massloss rates of progenitor star. We do not detect two other supernovae in the same galaxy, SN 1994I and SN 2005cs, and our observations place limits on the evolution of both supernovae at radio wavelengths. We also discuss the radio emission from the centre of M 51, in which we detect the Active Galactic Nucleus and other parts of the nuclear emission in the galaxy, and a possible detection of Component N. We discuss a few other sources, including the detection of a High mass X-ray Binary not detected by LoTSS, but with a flux density in the ILT image that matches well with higher frequency catalogues.

Authors:Dong-Xu Sun, Pei-Pei Zhang, Yi-Qing Guo, Wei Liu, Qiang Yuan

Abstract: The observations of the energy spectra of cosmic-ray have revealed complicated structures. Especially, spectral hardenings in the boron-to-carbon and boron-to-oxygen ratios above $\sim 200$ GV has been revealed by AMS-02 and DAMPE experiments. One scenario to account for the hardenings of secondary-to-primary ratios is the nuclear fragmentation of freshly accelerated particles around sources. In this work, we further study this scenario based on new observations of Galactic diffuse gamma rays by LHAASO and neutrinos by IceCube. We find that the spectra of cosmic ray nuclei, the diffuse ultra-high-energy gamma rays, and the Galactic component of neutrinos can be simultaneously explained, given an average confinement and interaction time of $\sim 0.25$ Myr around sources. These multi-messenger data thus provide evidence of non-negligible grammage of Galactic cosmic rays surrounding sources besides the traditional one during the propagation.

Authors:Parul Janagal, Samuel J. McSweeney, Manoneeta Chakraborty, N. D. Ramesh Bhat

Abstract: PSR J0026-1955 was independently discovered by the Murchison Widefield Array (MWA) recently. The pulsar exhibits subpulse drifting, where the radio emission from a pulsar appears to drift in spin phase within the main pulse profile, and nulling, where the emission ceases briefly. The pulsar showcases a curious case of drift rate evolution as it exhibits rapid changes between the drift modes and a gradual evolution in the drift rate within a mode. Here we report new analysis and results from observations of J0026-1955 made with the upgraded Giant Meterwave Radio Telescope (uGMRT) at 300-500 MHz. We identify two distinct subpulse drifting modes: A and B, with mode A sub-categorised into A0, A1, and A2, depending upon the drift rate evolutionary behaviour. Additionally, the pulsar exhibits short and long nulls, with an estimated overall nulling fraction of ~58%, which is lower than the previously reported value. Our results also provide evidence of subpulse memory across nulls and a consistent behaviour where mode A2 is often followed by a null. We investigate the drift rate modulations of J0026-1955 and put forward two different models to explain the observed drifting behaviour. We suggest that either a change in polar gap screening or a slow relaxation in the spark configuration could possibly drive the evolution in drift rates. J0026-1955 belongs to a rare subset of pulsars which exhibit subpulse drifting, nulling, mode changing, and drift rate evolution. It is, therefore, an ideal test bed for carousel models and to uncover the intricacies of pulsar emission physics.

Authors:Xin Sheng, Lizhong Zhang, Omer Blaes, Yan-Fei Jiang

Abstract: We present relativistic, radiation magnetohydrodynamic simulations of supercritical neutron star accretion columns in Cartesian geometry, including temperature-dependent, polarization-averaged Rosseland mean opacities accounting for classical electron scattering in a magnetic field. Just as in our previous pure Thomson scattering simulations, vertical oscillations of the accretion shock and horizontally propagating entropy waves (photon bubbles) are present in all our simulations. However, at high magnetic fields $\gtrsim10^{12}$~G, the magnetic opacities produce significant differences in the overall structure and dynamics of the column. At fixed accretion rate, increasing the magnetic field strength results in a shorter accretion column, despite the fact that the overall opacity within the column is larger. Moreover, the vertical oscillation amplitude of the column is reduced. Increasing the accretion rate at high magnetic fields restores the height of the column. However, a new, slower instability takes place at these field strengths because they are in a regime where the opacity increases with temperature. This instability causes both the average height of the column and the oscillation amplitude to substantially increase on a time scale of $\sim10$~ms. We provide physical explanations for these results, and discuss their implications for the observed properties of these columns, including mixed fan-beam/pencil-beam emission patterns caused by the oscillations.

Authors:Aysha Aamer, Matt Nicholl, Anders Jerkstrand, Sebastian Gomez, Samantha R. Oates, Stephen J. Smartt, Shubham Srivastav, Giorgos Leloudas, Joseph P. Anderson, Edo Berger, Thomas de Boer, Kenneth Chambers, Ting-Wan Chen, Lluís Galbany, Hua Gao, Benjamin P. Gompertz, Maider González-Bañuelos, Mariusz Gromadzki, Claudia P. Gutiérrez, Cosimo Inserra, Thomas B. Lowe, Eugene A. Magnier, Paolo A. Mazzali, Thomas Moore, Tomás E. Müller-Bravo, Miika Pursiainen, Armin Rest, Steve Schulze, Ken W. Smith, Jacco H. Terwel, Richard Wainscoat, David R. Young

Abstract: We present a detailed study on SN2019szu, a Type I superluminous supernova at $z=0.213$, that displayed unique photometric and spectroscopic properties. Pan-STARRS and ZTF forced photometry shows a pre-explosion plateau lasting $\sim$ 40 days. Unlike other SLSNe that show decreasing photospheric temperatures with time, the optical colours show an apparent temperature increase from $\sim$15000\,K to $\sim$20000\,K over the first 70 days, likely caused by an additional pseudo-continuum in the spectrum. Remarkably, the spectrum displays a forbidden emission line even during the rising phase of the light curve, inconsistent with an apparently compact photosphere. We show that this early feature is [O II] $\lambda\lambda$7320,7330. We also see evidence for [O III] $\lambda\lambda$4959, 5007, and [O III] $\lambda$4363 further strengthening this line identification. Comparing with models for nebular emission, we find that the oxygen line fluxes and ratios can be reproduced with $\sim$0.25\,M$_{\odot}$ of oxygen rich material with a density of $\sim10^{-15}\,\rm{g\,cm}^{-3}$. The low density suggests a circumstellar origin, but the early onset of the emission lines requires that this material was ejected within the final months before the terminal explosion, consistent with the timing of the precursor plateau. Interaction with denser material closer to the explosion likely produced the pseudo-continuum bluewards of $\sim$5500\,$\Angstrom$. We suggest that this event is one of the best candidates to date for a pulsational pair-instability ejection, with early pulses providing the low density material needed for the forbidden emission line, and collisions between the final shells of ejected material producing the pre-explosion plateau.

Authors:A. Paggi, F. Massaro, H. Peña-Herazo, V. Missaglia, A. Jimenez-Gallardo, F. Ricci, S. Ettori, G. Giovannini, F. Govoni, R. D. Baldi, B. Mingo, M. Murgia, E. Liuzzo, F. Galati

Abstract: We present the first results of the Chandra Cool Targets (CCT) survey of the Second Bologna Catalog (B2CAT) of powerful radio sources, aimed at investigating the extended X-ray emission surrounding these sources. For the first 33 sources observed in the B2CAT CCT survey, we performed both imaging and spectral X-ray analysis, producing multi-band Chandra images, and compared them with radio observations. To evaluate the presence of extended emission in the X-rays, we extracted surface flux profiles comparing them with simulated ACIS Point Spread Functions. We detected X-ray nuclear emission for 28 sources. In addition, we detected 8 regions of increased X-ray flux originating from radio hot-spots or jet knots, and a region of decreased flux, possibly associated with an X-ray cavity. We performed X-ray spectral analysis for 15 nuclei and found intrinsic absorption significantly larger than the Galactic values in four of them. We detected significant extended X-ray emission in five sources, and fitted their spectra with thermal models with gas temperatures $\sim 2 \text{ keV}$. In the case of B2.1 0742+31, the surrounding hot gas is compatible with the ICM of low luminosity clusters of galaxies, while the X-ray diffuse emission surrounding the highly disturbed WAT B2.3 2254+35 features a luminosity similar to those of relatively bright galaxy groups, although its temperature is similar to those of low luminosity galaxy clusters. These results highlight the power of the low-frequency radio selection, combined with short Chandra snapshot observations, to investigate the properties of the X-ray emission from radio sources.

Authors:Damiano F. G. Fiorillo, Victor Valera, Mauricio Bustamante, Walter Winter

Abstract: Next-generation ultra-high-energy (UHE) neutrino telescopes, presently under planning, will have the potential to probe the decay of heavy dark matter (DM) into UHE neutrinos, with energies in excess of $10^7$~GeV. Yet, this potential may be deteriorated by the presence of an unknown background of UHE neutrinos, cosmogenic or from astrophysical sources, not of DM origin and seemingly large enough to obscure the DM signature. We show that leveraging the angular and energy distributions of detected events safeguards future searches for DM decay against such backgrounds. We focus on the radio-detection of UHE neutrinos in the planned IceCube-Gen2 neutrino telescope, which we model in state-of-the-art detail. We report promising prospects for the discovery potential of DM decay into UHE neutrinos, the measurement of DM mass and lifetime, and limits on the DM lifetime, despite the presence of a large background, without prior knowledge of its size and shape.

Authors:Yize Dong, David J. Sand, Stefano Valenti, K. Azalee Bostroem, Jennifer E. Andrews, Griffin Hosseinzadeh, Emily Hoang, Daryl Janzen, Jacob E. Jencson, Michael Lundquist, Nicolas E. Meza Retamal, Jeniveve Pearson, Manisha Shrestha, Joshua Haislip, Vladimir Kouprianov, Daniel E. Reichart

Abstract: We perform a comprehensive search for optical precursor emission at the position of SN~2023ixf using data from the DLT40, ZTF and ATLAS surveys. By comparing the current data set with precursor outburst hydrodynamical model light curves, we find that the probability of a significant outburst within five years of explosion is low, and the circumstellar material (CSM) ejected during any possible precursor outburst is likely smaller than $\sim$0.015\msun. By comparing to a set of toy models, we find that, if there was a precursor outburst, the duration must have been shorter than $\sim$100 days for a typical brightness of $M_{r}\simeq-9$ mag or shorter than 200 days for $M_{r}\simeq-8$ mag; brighter, longer outbursts would have been discovered. Precursor activity like that observed in the normal type II SN~2020tlf ($M_{r}\simeq-11.5$) can be excluded in SN~2023ixf. If the dense CSM inferred by early flash spectroscopy and other studies is related to one or more precursor outbursts, then our observations indicate that any such outburst would have to be faint and only last for days to months, or it occurred more than five years prior to the explosion. Alternatively, any dense, confined CSM may not be due to eruptive mass loss from a single red supergiant (RSG) progenitor. Taken together, the results of SN~2023ixf and SN~2020tlf indicate that there may be more than one physical mechanism behind the dense CSM inferred around some normal type II SNe.

Authors:S. Scaringi Durham University, K. Breivik Flatiron Institute, T. B. Littenberg Marshall Space Flight Center, C. Knigge University of Southampton, P. J. Groot Radboud University SAAO University of Cape Town, M. Veresvarska Durham University

Abstract: The gravitational wave (GW) signals from the Galactic population of cataclysmic variables (CVs) have yet to be carefully assessed. Here we estimate these signals and evaluate their significance for LISA. First, we find that at least three known systems are expected to produce strong enough signals to be individually resolved within the first four years of LISA's operation. Second, CVs will contribute significantly to the LISA Galactic binary background, limiting the mission's sensitivity in the relevant frequency band. Third, we predict a spike in the unresolved GW background at a frequency corresponding to the CV minimum orbital period. This excess noise may impact the detection of other systems near this characteristic frequency. Fourth, we note that the excess noise spike amplitude and location associated with $P_{\rm{min}}\sim80~\mathrm{min}$ can be used to measure the CV space density and period bounce location with complementary and simple GW biases compared to the biases and selection effects plaguing samples selected from electromagnetic signals. Our results highlight the need to explicitly include the Galactic CV population in the LISA mission planning, both as individual GW sources and generators of background noise, as well as the exciting prospect of characterising the CV population through their GW emission.

Authors:Rodrigo Fernández, Oliver Just, Zewei Xiong, Gabriel Martínez-Pinedo

Abstract: The accretion disk formed after a neutron star merger is an important contributor to the total ejecta from the merger, and hence to the kilonova and the $r$-process yields of each event. Axisymmetric viscous hydrodynamic simulations of these disks can capture thermal mass ejection due to neutrino absorption and in the advective phase -- after neutrino cooling has subsided -- and are thus likely to provide a lower-limit to the total disk ejecta relative to MHD evolution. Here we present a comparison between two viscous hydrodynamic codes that have been used extensively on this problem over the past decade: ALCAR and FLASH. We choose a representative setup with a black hole at the center, and vary the treatment of viscosity and neutrino transport. We find good overall agreement ($\sim 10\%$ level) in most quantities. The average outflow velocity is sensitive to the treatment of the nuclear binding energy of heavy nuclei, showing a larger variation than other quantities. We post-process trajectories from both codes with the same nuclear network, and explore the effects of code differences on nucleosynthesis yields, heating rates, and kilonova light curves. For the latter, we also assess the effect of varying the number of tracer particles in reconstructing the spatial abundance distribution for kilonova light curve production.

Authors:M. Nicholl, S. Srivastav, M. D. Fulton, S. Gomez, M. E. Huber, S. R. Oates, P. Ramsden, L. Rhodes, S. J. Smartt, K. W. Smith, A. Aamer, J. P. Anderson, F. E. Bauer, E. Berger, T. de Boer, K. C. Chambers, P. Charalampopoulos, T. -W. Chen, R. P. Fender, M. Fraser, H. Gao, D. A. Green, L. Galbany, B. P. Gompertz, M. Gromadzki, C. P. Gutiérrez, D. A. Howell, C. Inserra, P. G. Jonker, M. Kopsacheili, T. B. Lowe, E. A. Magnier, S. L. McGee, T. Moore, T. E. Müller-Bravo, T. Pessi, M. Pursiainen, A. Rest, E. J. Ridley, B. J. Shappee, X. Sheng, G. P. Smith, M. A. Tucker, J. Vinkó, R. J. Wainscoat, P. Wiseman, D. R. Young

Abstract: We present the discovery and extensive follow-up of a remarkable fast-evolving optical transient, AT2022aedm, detected by the Asteroid Terrestrial impact Last Alert Survey (ATLAS). AT2022aedm exhibited a rise time of $9\pm1$ days in the ATLAS $o$-band, reaching a luminous peak with $M_g\approx-22$ mag. It faded by 2 magnitudes in $g$-band during the next 15 days. These timescales are consistent with other rapidly evolving transients, though the luminosity is extreme. Most surprisingly, the host galaxy is a massive elliptical with negligible current star formation. X-ray and radio observations rule out a relativistic AT2018cow-like explosion. A spectrum in the first few days after explosion showed short-lived He II emission resembling young core-collapse supernovae, but obvious broad supernova features never developed; later spectra showed only a fast-cooling continuum and narrow, blue-shifted absorption lines, possibly arising in a wind with $v\approx2700$ km s$^{-1}$. We identify two further transients in the literature (Dougie in particular, as well as AT2020bot) that share similarities in their luminosities, timescales, colour evolution and largely featureless spectra, and propose that these may constitute a new class of transients: luminous fast-coolers (LFCs). All three events occurred in passive galaxies at offsets of $\sim4-10$ kpc from the nucleus, posing a challenge for progenitor models involving massive stars or massive black holes. The light curves and spectra appear to be consistent with shock breakout emission, though usually this mechanism is associated with core-collapse supernovae. The encounter of a star with a stellar mass black hole may provide a promising alternative explanation.

Authors:Efrain Gatuzz, R. Mohapatra, C. Federrath, J. S. Sanders, A. Liu, S. A. Walker, C. Pinto

Abstract: It has been shown that the gas velocities within the intracluster medium (ICM) can be measured by applying novel XMM-Newton EPIC-pn energy scale calibration, which uses instrumental Cu Ka as reference for the line emission. Using this technique, we have measured the velocity distribution of the ICM for clusters involving AGN feedback and sloshing of the plasma within the gravitational well (Virgo and Centaurus) and a relaxed one (Ophiuchus). We present a detailed study of the kinematics of the hot ICM for these systems. First, we compute the velocity probability distribution functions (PDFs) from the velocity maps. We find that for all sources the PDF follows a normal distribution, with a hint for a multimodal distribution in the case of Ophiuchus. Then, we compute the velocity structure function (VSF) for all sources in order to study the variation with scale as well as the nature of turbulence in the ICM. We measure a turbulence driving scale of 10-20 kpc for the Virgo cluster, while the Ophiuchus cluster VSF reflects the absence of strong interaction between the ICM and a powerful Active Galactic Nucleus (AGN) at such spatial scales. For the former, we compute a dissipation time larger than the jet activity cycle, thus indicating that a more efficient heating process than turbulence is required to reach equilibrium. This is the first time that the VSF of the hot ICM has been computed using direct velocity measurements from X-ray astronomical observations.

Authors:Gabriele Bruni, Javier Moldón, Enrico Piconcelli, Francesca Panessa, Miguel Pérez-Torres, Manuela Bischetti, Chiara Feruglio, Giustina Vietri, Cristian Vignali, Luca Zappacosta, Ivano Saccheo

Abstract: In the past years, the results obtained by the WISSH quasar project provided a novel general picture on the distinctive multi-band properties of hyper-luminous ($L_{bol}>10^{47}$ erg/s) quasars at high redshift (z$\sim$2-4), unveiling interesting relations among active galactic nuclei, winds and interstellar medium, in these powerful sources at cosmic noon. Since 2022, we are performing a systematic and statistically-significant VLA study of the radio properties of WISSH. We carried out high-resolution VLA observations aiming at: 1) identifying young radio source from the broad-band spectral shape of these objects; 2) sample an unexplored high redshift/high luminosity regime, tracking possible evolutionary effects on the radio-loud/radio-quiet dichotomy; 3) quantifying orientation effects on the observed winds/outflows properties.

Authors:Junjie Mao, Frits Paerels, Matteo Guainazzi, Jelle S. Kaastra

Abstract: The past two decades have witnessed the rapid growth of our knowledge of the X-ray Universe thanks to flagship X-ray space observatories like XMM-Newton and Chandra. A significant portion of discoveries would have been impossible without the X-ray diffractive grating spectrometers aboard these two space observatories. We briefly overview the physical principles of diffractive grating spectrometers as the background to the beginning of a new era with the next-generation (diffractive and non-diffractive) high-resolution X-ray spectrometers. This chapter focuses on the Reflection Grating Spectrometer aboard XMM-Newton, which provides high-quality high-resolution spectra in the soft X-ray band. Its performance and excellent calibration quality have allowed breakthrough advancements in a wide range of astrophysical topics. For the benefit of new learners, we illustrate how to reduce RGS imaging, timing, and spectral data.

Authors:Zhiwei Chen NAOC

Abstract: Gravitational waves emitted from stellar binary black hole (sBBH) mergers can be gravitationally lensed by intervening galaxies and detected by future ground-based detectors. A large amount of effort has been put into the estimation of the detection rate of lensed sBBH originating from the evolution of massive binary stars (EMBS channel). However, sBBHs produced by the dynamical interaction in dense clusters (dynamical channel) may also be dominant in our universe and their intrinsic distribution of physical properties can be significantly different from those produced by massive stars, especially mass and redshift distribution. In this paper, we investigate the event rate of lensed sBBHs produced via dynamical channel by Monte Carlo simulations and the number is $16_{-12}^{+4.7} $ $\rm yr^{-1}$ for the Einstein telescope and $24_{-17}^{+6.8}$ $ \rm yr^{-1}$ for Cosmic Explorer, of which the median is about $\sim 2$ times the rate of sBBHs originated from EMBS channel (calibrated by the local merger rate density estimated for the dynamical and the EMBS channel, i.e., $\sim 14_{-10}^{+4.0}$ and $19_{-3.0}^{+42} \rm Gpc^{-3}yr^{-1}$ respectively). Therefore, one may constrain the fraction of both EMBS and dynamical channels through the comparison of the predicted and observed number of lensed sBBH events statistically.

Authors:Hiroki Kawai, Yohko Tsuboi, Wataru B. Iwakiri, Yoshitomo Maeda, Satoru Katsuda, Ryo Sasaki, Junya Kohara, MAXI TEAM

Abstract: We report on the results of our simultaneous observations of three large stellar flares with soft X-rays (SXRs) and an H$\mathrm{\alpha}$ emission line from two binary systems of RS CVn type. The energies released in the X-ray and H$\mathrm{\alpha}$ emissions during the flares were $10^{36}$--$10^{38}$ and $10^{35}$--$10^{37}$ erg, respectively. It renders the set of the observations as the first successful simultaneous X-ray/H$\mathrm{\alpha}$ observations of the stellar flares with energies above $10^{35}$ erg; although the coverage of the H$\mathrm{\alpha}$ observations of the stellar flares with energies above $10^{35}$ erg; although the coverage of the H$\mathrm{\alpha}$ observations was limited, with $\sim$10\% of the $e$-folding time in the decay phase of the flares, that of the SXR ones was complete. Combining the obtained physical parameters and those in literature for solar and stellar flares, we obtained a good proportional relation between the emitted energies of X-ray and H$\mathrm{\alpha}$ emissions for a flare energy range of $10^{29}$--$10^{38}$ erg. The ratio of the H$\mathrm{\alpha}$-line to bolometric X-ray emissions was $\sim$0.1, where the latter was estimated by converting the observed SXR emission to that in the 0.1--100 keV band according to the best-fitting thin thermal model. We also found that the $e$-folding times of the SXR and H$\mathrm{\alpha}$ light curves in the decaying phase of a flare are in agreement for a time range of $1$--$10^4$~s. Even very large stellar flares with energies of six orders of magnitude larger than the most energetic solar flares follow the same scaling relationships with solar and much less energetic stellar flares. This fact suggests that their physical parameters can be estimated on the basis of the known physics of solar and stellar flares.

Authors:S. E. Motta, T. M. Belloni

Abstract: Context. The study of Quasi-Periodic Oscillations (QPO) at low and high frequency in the variability of the high-energy emission from black-hole binaries and their physical interpretation in terms of signatures of General Relativity in the strong-field regime. Aims. To understand the nature of the 67 Hz QPOs observed in the X-ray emission of the peculiar black-hole binary GRS 1915+105 within the general classification of QPO and to determine the spin of the black hole in the system by applying the Relativistic Precession Model (RPM). Methods. Within the RPM, the only relativistic frequency that is stable in time over a large range of accretion rates and can be as low as 67 Hz (for a black-hole mass as measured dynamically) is the Lense-Thirring frequency at the Innermost Stable Circular Orbit (ISCO). In the application of the model, this corresponds to type-C QPOs. Under this assumption, it is possible to measure the spin of the black hole. We re-analysed a large number of RossiXTE observations to check whether other timing features confirm this hypothesis. Results. The identification of the 67 Hz QPO as the Lense-Thirring frequency at ISCO yields a value of 0.706 +/- 0.034 for the black hole spin. With this spin, the only two QPO detections at higher frequencies available in the literature are consistent with being orbital frequencies at a radius outside ISCO. The high-frequency bumps often observed at frequencies between 10 and 200 Hz follow the correlation expected for orbital and periastron-precession frequencies at even larger radii.

Authors:Simeon Reusch

Abstract: Using the Zwicky Transient Facility (ZTF) and other observatories, we have identified three candidate Tidal Disruption Events (TDEs) in spatial and temporal coincidence with high-energy neutrinos detected by IceCube: AT2019dsg, AT2019fdr and AT2019aalc. All three of these events have been shown to be able to produce high-energy neutrinos. In these proceedings, I will give an overview of Tidal Disruption Events, outline our follow-up program with ZTF, describe the observations carried out for each of those coincident events and highlight their similarities and differences.

Authors:Avinash Tiwari, Aditya Vijaykumar, Shasvath J. Kapadia, Giacomo Fragione, Sourav Chatterjee

Abstract: The motion of the center of mass of a coalescing binary black hole (BBH) in a gravitational potential imprints a line-of-sight acceleration (LOSA) onto the emitted gravitational wave (GW) signal. The acceleration could be sufficiently large in dense stellar environments, such as globular clusters (GCs), to be detectable with next-generation space-based detectors. In this work, we use outputs of the \textsc{cluster monte carlo (cmc)} simulations of dense star clusters to forecast the distribution of detectable LOSAs in DECIGO and LISA eras. We study the effect of cluster properties -- metallicity, virial and galactocentric radii -- on the distribution of detectable accelerations, account for cosmologically-motivated distributions of cluster formation times, masses, and metallicities, and also incorporate the delay time between the formation of BBHs and their merger in our analysis. We find that larger metallicities provide a larger fraction of detectable accelerations by virtue of a greater abundance of relatively lighter BBHs, which allow a higher number of GW cycles in the detectable frequency band. Conversely, smaller metallicities result in fewer detections, most of which come from relatively more massive BBHs with fewer cycles but larger LOSAs. We similarly find correlations between the virial radii of the clusters and the fractions of detectable accelerations. Our work, therefore, provides an important science case for space-based GW detectors in the context of probing GC properties via the detection of LOSAs of merging BBHs.

Authors:Nikolai Chugai

Abstract: I explore a possibility to estimate an upper limit of the current iron abundance of the barion matter. The upper limit is determined by the minimal iron abundance, at which the gamma-ray background, produced by the decay of $^{56}$Ni synthesised in the Universe to date, contradicts the observational MeV gamma-ray background. I calculate the gamma-ray background from SNe~Ia and SNe~II with the gamma-ray scattering and absorption in supernova envelope. It is shown that the model background does not contradict the observed MeV background, if the present day iron abundance of the barion matter is less than 15\% of the solar abundance.

Authors:Kenta Hotokezaka, Masaomi Tanaka, Daiji Kato, Gediminas Gaigalas

Abstract: The late-time spectra of the kilonova AT 2017gfo associated with GW170817 exhibit a strong emission line feature at $2.1\,{\rm \mu m}$. The line structure develops with time and there is no apparent blue-shifted absorption feature in the spectra, suggesting that this emission line feature is produced by electron collision excitation. We attribute the emission line to a fine structure line of Tellurium (Te) III, which is one of the most abundant elements in the second r-process peak. By using a synthetic spectral modeling including fine structure emission lines with the solar r-process abundance pattern beyond the first r-process peak, i.e., atomic mass numbers $A\gtrsim 88$, we demonstrate that [Te III] $2.10\,\rm \mu m$ is indeed expected to be the strongest emission line in the near infrared region. We estimate that the required mass of Te III is $\sim 10^{-3}M_{\odot}$, corresponding to the merger ejecta of $0.05M_{\odot}$, which is in agreement with the mass estimated from the kilonova light curve.

Authors:Sheng-Lun Xie, Yi Zhao, Wang-Chen Xue, Yun-Wei Yu, Shao-Lin Xiong, Heng Yu, Ce Cai, Shuang-Nan Zhang

Abstract: Over a period of four active episodes between January 2021 and January 2022, the magnetar SGR J1935+2154 emitted a total of 343 bursts observed by the \textit{Fermi}/GBM and 82 bursts observed by GECAM-B. Temporal and spectral analyses reveal that the bursts have an average duration of 145 ms and a fluence ranging from $1.2 \times 10^{-9} \ \mathrm{erg \cdot cm^{-2}}$ to $4.1 \times 10^{-4} \ \mathrm{erg \cdot cm^{-2}}$ (8 - 200 keV). The spectral properties of these bursts are similar to those of earlier active episodes. Specifically, we find that the emission area of the Double Black Body (BB2) model shows a Log-Linear correlation to its temperature, and there is a weak relation between fluence and $E_{\mathrm{peak}}$/$\alpha$ in the CPL model. However, we note that the temperature distributions of BB2/BB models in GECAM-B are different from those in \textit{Fermi}/GBM, due to differences in the energy range used for fitting. To understand this difference, we propose a Multi-Temperature Black Body (MBB) model for analyzing thermal radiation, assuming that the BB temperatures follow a power law distribution. Our analysis shows the minimum temperature $kT_{\mathrm{min}} \sim 5$ keV of the MBB model is consistent between \textit{Fermi}/GBM and GECAM-B, and reveals the spectra of magnetar bursts tending to be soft, which may be composed of multiple BB components. The slope of the temperature distribution is steep which indicates that the majority of the BB temperatures are concentrated around the minimum temperature.

Authors:Chengyu Shao, Sujie Lin, Lili Yang

Abstract: With the breakthrough in PeV gamma-ray astronomy brought by the LHAASO experiment, high-energy sky is getting more completed than before. Lately LHAASO Collaboration reported the observation of a gamma-ray diffuse emission with energy up to the PeV level from both the inner and outer Galactic plane. In these spectra, there is one bump which is hard to explain by the conventional cosmic-ray transport scenarios. Therefore, we introduce two extra components corresponding to unresolved sources with exponential-cutoff-power-law (ECPL) spectral shape, one with index of 2.4, and 30 TeV cutoff energy, and another with index of 2.3 and 2 PeV cutoff energy. With our constructed model, we simulate the Galactic diffuse neutrino flux and find our results are in full agreement with latest IceCube Galactic plane search. We estimate the Galactic neutrino contribute of $\sim 9\%$ of astrophysical neutrinos at 20 TeV. In the high-energy regime, as expected most of neutrinos observed by IceCube should be from extra-galaxy.

Authors:S. R. Oates, N. P. M. Kuin, M. Nicholl, F. Marshall, E. Ridley, K. Boutsia, A. A. Breeveld, D. A. H. Buckley, S. B. Cenko, M. De Pasquale, P. G. Edwards, M. Gromadzki, R. Gupta, S. Laha, N. Morrell, M. Orio, S. B. Pandey, M. J. Page, K. L. Page, T. Parsotan, A. Rau, P. Schady, J. Stevens, P. J. Brown, P. A. Evans, C. Gronwall, J. A. Kennea, N. J. Klingler, M. H. Siegel, A. Tohuvavohu, E. Ambrosi, S. D. Barthelmy, A. P. Beardmore, M. G. Bernardini, C. Bonnerot, S. Campana, R. Caputo, S. Ciroi, G. Cusumano, A. D'Ai, P. D'Avanzo, V. D'Elia, P. Giommi, D. H. Hartmann, H. A. Krimm, D. B. Malesani, A. Melandri, J. A. Nousek, P. T. O'Brien, J. P. Osborne, C. Pagani, D. M. Palmer, M. Perri, J. L. Racusin, T. Sakamoto, B. Sbarufatti, J. E. Schlieder, G. Tagliaferri, E. Troja, D. Xu

Abstract: We report the discovery of Swift J221951-484240 (hereafter: J221951), a luminous slow-evolving blue transient that was detected by the Neil Gehrels Swift Observatory Ultra-violet/Optical Telescope (Swift/UVOT) during the follow-up of Gravitational Wave alert S190930t, to which it is unrelated. Swift/UVOT photometry shows the UV spectral energy distribution of the transient to be well modelled by a slowly shrinking black body with an approximately constant temperature of T~2.5x10^4 K. At a redshift z=0.5205, J221951 had a peak absolute magnitude of M_u,AB = -23 mag, peak bolometric luminosity L_max=1.1x10^45 erg s^-1 and a total radiated energy of E>2.6x10^52 erg. The archival WISE IR photometry shows a slow rise prior to a peak near the discovery date. Spectroscopic UV observations display broad absorption lines in N V and O VI, pointing toward an outflow at coronal temperatures. The lack of emission in the higher H~Lyman lines, N I and other neutral lines is consistent with a viewing angle close to the plane of the accretion or debris disc. The origin of J221951 can not be determined with certainty but has properties consistent with a tidal disruption event and the turn-on of an active galactic nucleus.

Authors:Matthew Kerr, Wade Duvall, Neil Johnson, Richard Woolf, J. Eric Grove, Hannah Kim

Abstract: We present a maximum likelihood (ML) algorithm that is fast enough to detect gamma-ray transients in real time on low-performance processors often used for space applications. We validate the routine with simulations and find that, relative to algorithms based on excess counts, the ML method is nearly twice as sensitive, allowing detection of 240-280% more short gamma-ray bursts. We characterize a reference implementation of the code, estimating its computational complexity and benchmarking it on a range of processors. We exercise the reference implementation on archival data from the Fermi Gamma-ray Burst Monitor (GBM), verifying the sensitivity improvements. In particular, we show that the ML algorithm would have detected GRB 170817A even if it had been nearly four times fainter. We present an ad hoc but effective scheme for discriminating transients associated with background variations. We show that the on-board localizations generated by ML are accurate, but that refined off-line localizations require a detector response matrix with about ten times finer resolution than is current practice. Increasing the resolution of the GBM response matrix could substantially reduce the few-degree systematic uncertainty observed in the localizations of bright bursts.

Authors:John Ryan Westernacher-Schneider, Jonathan Zrake, Andrew MacFadyen, Zoltán Haiman

Abstract: We show that gas disks around the components of an orbiting binary system (so-called minidisks) may be susceptible to a resonant instability which causes the minidisks to become significantly eccentric. Eccentricity is injected by, and also induces, regular impacts between the minidisks at roughly the orbital period of the binary. Eccentric minidisks are seen in vertically integrated, two-dimensional simulations of a circular, equal-mass binary accreting from a circumbinary gas disk with a $\Gamma$-law equation of state. Minidisk eccentricity is suppressed by the use of an isothermal equation of state. However, the instability still operates, and can be revealed in a minimal disk-binary simulation by removing the circumbinary disk, and feeding the minidisks from the component positions. Minidisk eccentricity is also suppressed when the gravitational softening length is large ($\gtrsim 4\%$ of the binary semi-major axis), suggesting that its absence could be an artifact of widely adopted numerical approximations; a follow-up study in three dimensions with well-resolved, geometrically thin minidisks (aspect ratios $\lesssim 0.02$) may be needed to assess whether eccentric minidisks can occur in real astrophysical environments. If they can, the electromagnetic signature may be important for discriminating between binary and single black hole scenarios for quasi-periodic oscillations in active galactic nuclei, which may in turn aid in targeted searches with pulsar timing arrays for individual supermassive black hole binary sources of low-frequency gravitational waves.

Authors:Tathagata Ghosh, Anish Ghoshal, Huai-Ke Guo, Fazlollah Hajkarim, Stephen F King, Kuver Sinha, Xin Wang, Graham White

Abstract: In this paper, we analyse sound waves arising from a cosmic phase transition where the full velocity profile is taken into account as an explanation for the gravitational wave spectrum observed by multiple pulsar timing array groups. Unlike the broken power law used in the literature, in this scenario the power law after the peak depends on the macroscopic properties of the phase transition, allowing for a better fit with pulsar timing array (PTA) data. We compare the best fit with that obtained using the usual broken power law and, unsurprisingly, find a better fit with the gravitational wave (GW) spectrum that utilizes the full velocity profile. We then discuss models that can produce the best-fit point and complementary probes using CMB experiments and searches for light particles in DUNE, IceCUBE-Gen2, neutrinoless double beta decay, and forward physics facilities at the LHC like FASER nu, etc.

Authors:Sergiy S. Vasylyev, Yi Yang, Alexei V. Filippenko, Kishore Patra, Thomas G. Brink, Lifan Wang, Ryan Chornock, Rafaella Margutti, Elinor L. Gates, Adam J. Burgasser, Preethi R. Karpoor, Natalie LeBaron, Emma Softich, Christopher A. Theissen, Eli Wiston, WeiKang Zheng

Abstract: We present six epochs of optical spectropolarimetry of the Type II supernova (SN) 2023ixf ranging from $\sim$ 2 to 15 days after the explosion. Polarimetry was obtained with the Kast double spectrograph on the Shane 3 m telescope at Lick Observatory, representing the earliest such observations ever captured for an SN. We observe a high continuum polarization $p_{\text{cont}} \approx 1$ % on days +1.4 and +2.5 before dropping to 0.5 % on day +3.5, persisting at that level up to day +14.5. Remarkably, this change coincides temporally with the disappearance of highly ionized "flash" features. The decrease of the continuum polarization is accompanied by a $\sim 70^\circ$ rotation of the polarization position angle ($PA$) as seen across the continuum. The early evolution of the polarization may indicate different geometric configurations of the electron-scattering atmosphere as seen before and after the disappearance of the emission lines associated with highly-ionized species (e.g., He II, C IV, N III), which are likely produced by elevated mass loss shortly prior to the SN explosion. We interpret the rapid change of polarization and $PA$ from days +2.5 to +4.5 as the time when the SN ejecta emerge from the dense asymmetric circumstellar material (CSM). The temporal evolution of the continuum polarization and the $PA$ is consistent with an aspherical SN explosion that exhibits a distinct geometry compared to the CSM. The rapid follow-up spectropolarimetry of SN 2023ixf during the shock ionization phase reveals an exceptionally asymmetric mass-loss process leading up to the explosion.

Authors:Tushar Mondal, Pallavi Bhat

Abstract: Magnetorotational instability (MRI)-driven turbulence and dynamo phenomena are analyzed using direct statistical simulations. Our approach begins by developing a unified mean-field model that combines the traditionally decoupled problems of the large-scale dynamo and angular-momentum transport in accretion disks. The model consists of a hierarchical set of equations, capturing up to the second-order cumulants, while a statistical closure approximation is employed to model the three-point correlators. We highlight the web of interactions that connect different components of stress tensors -- Maxwell, Reynolds, and Faraday -- through shear, rotation, correlators associated with mean fields, and nonlinear terms. We determine the dominant interactions crucial for the development and sustenance of MRI turbulence. Our general mean field model for the MRI-driven system allows for a self-consistent construction of the electromotive force, inclusive of inhomogeneities and anisotropies. Within the realm of large-scale magnetic field dynamo, we identify two key mechanisms -- the rotation-shear-current effect and the rotation-shear-vorticity effect -- that are responsible for generating the radial and vertical magnetic fields, respectively. We provide the explicit (nonperturbative) form of the transport coefficients associated with each of these dynamo effects. Notably, both of these mechanisms rely on the intrinsic presence of large-scale vorticity dynamo within MRI turbulence.

Authors:C. W. James

Abstract: Regardless of whether or not all fast radio bursts (FRBs) repeat, those that do form a population with a distribution of rates. This work considers a power-law model of this population, with rate distribution $\Phi_r \sim R^{\gamma_r}$ between $R_{\rm min}$ and $R_{\rm max}$. The zDM code is used to model the probability of detecting this population as either apparently once-off or repeat events as a function of redshift, $z$, and dispersion measure, DM. I demonstrate that in the nearby Universe, repeating sources can contribute significantly to the total burst rate. This causes an apparent deficit in the total number of observed sources (once-off and repeaters) relative to the distant Universe that will cause a bias in FRB population models. Thus instruments with long exposure times should explicitly take repetition into account when fitting the FRB population. I then fit data from The Canadian Hydrogen Intensity Mapping Experiment (CHIME). The relative number of repeat and apparently once-off FRBs, and their DM, declination, and burst rate distributions, can be well-explained by 50--100\% of CHIME single FRBs being due to repeaters, with $R_{\rm max} > 0.75$ day$^{-1}$ above $10^{39}$ erg, and ${\gamma_r} = -2.2_{-0.8}^{+0.6}$. This result is surprisingly consistent with follow-up studies of FRBs detected by the Australian Square Kilometre Array Pathfinder (ASKAP). Thus the evidence suggests that CHIME and ASKAP view the same repeating FRB population, which is responsible not just for repeating FRBs, but the majority of apparently once-off bursts. For greater quantitative accuracy, non-Poissonian arrival times, second-order effects in the CHIME response, and a simultaneous fit to the total FRB population parameters, should be treated in more detail in future studies.

Authors:Yongyun Chen, Qiusheng Gu, Junhui Fan, Xiaoling Yu, Xiaogu Zhong, Hongyu Liu, Nan Ding, Dingrong Xiong, Xiaotong Guo

Abstract: We study the general physical properties of Fermi blazars using the Fermi fourth source catalog data (4FGL-DR2). The quasi-simultaneous multiwavelength data of Fermi blazar are fitted by using the one-zone leptonic model to obtain some physical parameters, such as jet power, magnetic field and Doppler factor. We study the distributions of the derived physical parameter as a function of black hole mass and accretion disk luminosity. The main results are as follows. (1) For a standard thin accretion disk, the jet kinetic power of most FSRQs can be explained by the BP mechanism. However, the jet kinetic power of most BL Lacs can not be explained by both the BZ mechanism or the BP mechanism. The BL Lacs may have ADAFs surrounding their massive black holes. (2) After excluding the redshift, there is a moderately strong correlation between the jet kinetic power and jet radiation power and the accretion disk luminosity for Fermi blazars. These results confirm a close connection between jet and accretion. The jet kinetic power is slightly larger than the accretion disk luminosity for Fermi blazars. (3) There is a significant correlation between jet kinetic power and gamma-ray luminosity and radio luminosity for Fermi blazars, which suggests that gamma-ray luminosity and radio luminosity can be used to indicate the jet kinetic power.

Authors:Raúl Carballo-Rubio, Francesco Di Filippo, Stefano Liberati, Matt Visser

Abstract: Infrared observations of Sgr A$^*$ and M87$^*$ are incompatible with the assumption that these sources have physical surfaces in thermal equilibrium with their accreting environments. In this paper we discuss a general parametrization of the energy balance in a horizonless object, which permits to quantify how close a horizonless object is in its behavior to a black hole, and analyze the timescale in which its surface can thermalize. We show that the thermalization timescale is unbounded, growing large for objects that mimic closely the behavior of a black hole (and being infinite for the latter). In particular, the thermalization timescale is proportional to the time that energy spends inside the horizonless object due to propagation and interactions with the bulk. Hence, these observations can be used to quantitatively restrict the dynamical behavior of horizonless objects, without being able to discard the existence of a physical surface.

Authors:Shriya Soma, Horst Stöcker, Kai Zhou

Abstract: Gravitational Waves (GWs) from coalescing binaries carry crucial information about their component sources, like mass, spin and tidal effects. This implies that the analysis of GW signals from binary neutron star mergers can offer unique opportunities to extract information about the tidal properties of NSs, thereby adding constraints to the NS equation of state. In this work, we use Deep Learning (DL) techniques to overcome the computational challenges confronted in conventional methods of matched-filtering and Bayesian analyses for signal-detection and parameter-estimation. We devise a DL approach to classify GW signals from binary black hole and binary neutron star mergers. We further employ DL to analyze simulated GWs from binary neutron star merger events for parameter estimation, in particular, the regression of mass and tidal deformability of the component objects. The results presented in this work demonstrate the promising potential of DL techniques in GW analysis, paving the way for further advancement in this rapidly evolving field. The proposed approach is an efficient alternative to explore the wealth of information contained within GW signals of binary neutron star mergers, which can further help constrain the NS EoS.

Authors:Vishal Parmar, H. C. Das, M. K. Sharma, S. K. Patra

Abstract: Over the past two decades, significant strides have been made in the study of Dark Matter (DM) admixed neutron stars and their associated properties. However, an intriguing facet regarding the effect of DM on magnetized neutron stars still remains unexplored. This study is carried out to analyse the properties of DM admixed magnetized neutron stars. The equation of state for the DM admixed neutron star is calculated using the relativistic mean-field model with the inclusion of a density-dependent magnetic field. Several macroscopic properties such as mass, radius, particle fractions, tidal deformability, and the $f$-mode frequency are calculated with different magnetic field strengths and DM configurations. The equation of state is softer with the presence of DM as well as for the parallel components of the magnetic field, and vice-versa for the perpendicular one. Other macroscopic properties, such as mass, radius, tidal deformability, etc., are also affected by both DM and the magnetic fields. The change in the magnitude of different neutron star observables is proportional to the amount of DM percentage and the strength of the magnetic field. We observe that the change is seen mainly in the core part of the star without affecting the crustal properties.

Authors:A. V. Karpova, D. A. Zyuzin, Yu. A. Shibanov, M. R. Gilfanov

Abstract: The Fermi catalogue contains about 2000 unassociated $\gamma$-ray sources. Some of them were recently identified as pulsars, including so called redbacks and black widows, which are millisecond pulsars in tight binary systems with non- and partially-degenerate low-mass stellar companions irradiated by the pulsar wind. We study a likely optical and X-ray counterpart of the Fermi source 4FGL J2054.2+6904 proposed earlier as a pulsar candidate. We use archival optical data as well as Swift/XRT and SRG/eROSITA X-ray data to clarify its nature. Using Zwicky Transient Facility data in $g$ and $r$ bands spanning over 4.7 years, we find a period of $\approx$7.5 h. The folded light curve has a smooth sinusoidal shape with the peak-to-peak amplitude of $\approx$0.4 mag. The spectral fit to the optical spectral energy distribution of the counterpart candidate gives the star radius of 0.5$\pm$0.1$R_\odot$ and temperature of 5500$\pm$300 K implying a G2--G9-type star. Its X-ray spectrum is well fitted by an absorbed power law with the photon index of 1.0$\pm$0.3 and unabsorbed flux of $\approx 2\times10^{-13}$ erg s$^{-1}$ cm$^{-2}$. All the properties of 4FGL J2054.2$+$6904 and its presumed counterpart suggest that it is a member of the redback family.

Authors:Luke J. Shingles, Christine E. Collins, Vimal Vijayan, Andreas Flörs, Oliver Just, Gerrit Leck, Zewei Xiong, Andreas Bauswein, Gabriel Martínez-Pinedo, Stuart A. Sim

Abstract: We present three-dimensional radiative transfer calculations for the ejecta from a neutron star merger that include line-by-line opacities for tens of millions of bound-bound transitions, composition from an r-process nuclear network, and time-dependent thermalization of decay products from individual $\alpha$ and $\beta^-$ decay reactions. In contrast to expansion opacities and other wavelength-binned treatments, a line-by-line treatment enables us include fluorescence effects and associate spectral features with the emitting and absorbing lines of individual elements. We find variations in the synthetic observables with both the polar and azimuthal viewing angles. The spectra exhibit blended features with strong interactions by Ce III, Sr II, Y II, and Zr II that vary with time and viewing direction. We demonstrate the importance of wavelength-calibration of atomic data using a model with calibrated Sr, Y, and Zr data, and find major differences in the resulting spectra, including a better agreement with AT2017gfo. The synthetic spectra for near-polar inclination show a feature at around 8000 A, similar to AT2017gfo. However, they evolve on a more rapid timescale, likely due to the low ejecta mass (0.005 M$_\odot$) as we take into account only the early ejecta. The comparatively featureless spectra for equatorial observers gives a tentative prediction that future observations of edge-on kilonovae will appear substantially different from AT2017gfo. We also show that 1D models obtained by spherically averaging the 3D ejecta lead to dramatically different direction-integrated luminosities and spectra compared to full 3D calculations.

Authors:Edward M. Cackett, Jonathan Gelbord, Aaron J. Barth, Gisella De Rosa, Rick Edelson, Michael R. Goad, Yasaman Homayouni, Keith Horne, Erin A. Kara, Gerard A. Kriss, Kirk T. Korista, Hermine Landt, Rachel Plesha, Nahum Arav, Misty C. Bentz, Benjamin D. Boizelle, Elena Dalla Bonta, Maryam Dehghanian, Fergus Donnan, Pu Du, Gary J. Ferland, Carina Fian, Alexei V. Filippenko, Diego H. Gonzalez Buitrago, Catherine J. Grier, Patrick B. Hall, Chen Hu, Dragana Ilic, Jelle Kaastra, Shai Kaspi, Christopher S. Kochanek, Andjelka B. Kovacevic, Daniel Kynoch, Yan-Rong Li, Jacob N. McLane, Missagh Mehdipour, Jake A. Miller, John Montano, Hagai Netzer, Christos Panagiotou, Ethan Partington, Luka C. Popovic, Daniel Proga, Daniele Rogantini, David Sanmartim, Matthew R. Siebert, Thaisa Storchi-Bergmann, Marianne Vestergaard, Jian-Min Wang, Tim Waters, Fatima Zaidouni

Abstract: The AGN STORM 2 campaign is a large, multiwavelength reverberation mapping project designed to trace out the structure of Mrk 817 from the inner accretion disk to the broad emission line region and out to the dusty torus. As part of this campaign, Swift performed daily monitoring of Mrk 817 for approximately 15 months, obtaining observations in X-rays and six UV/optical filters. The X-ray monitoring shows that Mrk 817 was in a significantly fainter state than in previous observations, with only a brief flare where it reached prior flux levels. The X-ray spectrum is heavily obscured. The UV/optical light curves show significant variability throughout the campaign and are well correlated with one another, but uncorrelated with the X-rays. Combining the Swift UV/optical light curves with Hubble UV continuum light curves, we measure interband continuum lags, $\tau(\lambda)$, that increase with increasing wavelength roughly following $\tau(\lambda) \propto \lambda^{4/3}$, the dependence expected for a geometrically thin, optically thick, centrally illuminated disk. Modeling of the light curves reveals a period at the beginning of the campaign where the response of the continuum is suppressed compared to later in the light curve - the light curves are not simple shifted and scaled versions of each other. The interval of suppressed response corresponds to a period of high UV line and X-ray absorption, and reduced emission line variability amplitudes. We suggest that this indicates a significant contribution to the continuum from the broad line region gas that sees an absorbed ionizing continuum.

Authors:Zeinab Rezaei

Abstract: Fuzzy dark matter (FDM), a practical alternative to cold dark matter, can exist in compact stars. Here, applying the FDM equation of state (EoS) constrained by CMB and large-scale structure data, we calculate the structure of relativistic stars in the presence of FDM. For this aim, the EoS for the visible matter in neutron stars, quark stars, and hybrid stars from the observational data are employed. A piecewise polytropic EoS constrained by the observational data of GW170817 and the data of six low-mass X-ray binaries with thermonuclear burst or the symmetry energy of the nuclear interaction describes the neutron star matter. For quark star matter, we apply the EoSs within the Bayesian statistical approach using the mass and radius measurements of PSR J0030+0451 from NICER. Employing the two-fluid formalism, we study the structure of FDM admixed relativistic stars.

Authors:R. Ringuette, K. D. Kuntz, D. Koutroumpa, P. Kaaret, D. LaRocca, J. Richardson

Abstract: The study of solar wind charge exchange (SWCX) emission is vital to both the X-ray astrophysics and heliophysics communities. SWCX emission contaminates all astrophysical observations in X-rays regardless of the direction. Ignoring this contribution to X-ray spectra can lead to erroneous conclusions regarding the astrophysical plasmas along the line of sight due to the similar spectral distributions of SWCX and several common types of more distant astrophysical plasmas. Since its discovery, literature has distinguished between diffuse SWCX emission resulting from solar wind neutral interactions within the terrestrial magnetosphere, called magnetospheric SWCX, and similar interactions occurring more generally throughout the heliosphere, called heliospheric SWCX. Here, we build upon previous work validating a modeling method for the heliospheric SWCX contribution in X-ray spectra obtained with a medium resolution CubeSat instrument named HaloSat at low ecliptic latitudes. We now apply this model to a specially designed set of extended observations with the same instrument and successfully separate the spectral contributions of the astrophysical background and the heliospheric SWCX from the remaining contributions. Specifically, we find significant excess emission for four observations in the O VII emission line not explained by other sources, possibly indicative of magnetospheric SWCX. We discuss these results in comparison with simulation results publicly available through the Community Coordinated Modeling Center. We also report an absorbed high-temperature component in two of the twelve fields of view analyzed.

Authors:Ligong Bian, Shuailiang Ge, Jing Shu, Bo Wang, Xing-Yu Yang, Junchao Zong

Abstract: Very recently, several pulsar timing array collaborations, including CPTA, EPTA, and NANOGrav, reported their results from searches for an isotropic stochastic gravitational wave background (SGWB), with each finding positive evidence for SGWB. In this work, we assessed the credibility of interpreting the Hellings-Downs correlated free-spectrum process of EPTA, PPTA, and NANOGrav as either the result of supermassive black hole binary mergers or various stochastic SGWB sources that originated in the early Universe, including first-order phase transitions, cosmic strings, domain walls, and large-amplitude curvature perturbations. Our observations show that the current new datasets do not display a strong preference for any specific SGWB source based on Bayesian analysis.

Authors:A. Acharyya The VERITAS Collaboration, C. B. Adams The VERITAS Collaboration, A. Archer The VERITAS Collaboration, P. Bangale The VERITAS Collaboration, J. T. Bartkoske The VERITAS Collaboration, P. Batista The VERITAS Collaboration, W. Benbow The VERITAS Collaboration, A. Brill The VERITAS Collaboration, J. H. Buckley The VERITAS Collaboration, J. L. Christiansen The VERITAS Collaboration, A. J. Chromey The VERITAS Collaboration, M. Errando The VERITAS Collaboration, A. Falcone The VERITAS Collaboration, Q. Feng The VERITAS Collaboration, G. M. Foote The VERITAS Collaboration, L. Fortson The VERITAS Collaboration, A. Furniss The VERITAS Collaboration, G. Gallagher The VERITAS Collaboration, W. Hanlon The VERITAS Collaboration, D. Hanna The VERITAS Collaboration, O. Hervet The VERITAS Collaboration, C. E. Hinrichs The VERITAS Collaboration, J. Hoang The VERITAS Collaboration, J. Holder The VERITAS Collaboration, T. B. Humensky The VERITAS Collaboration, W. Jin The VERITAS Collaboration, P. Kaaret The VERITAS Collaboration, M. Kertzman The VERITAS Collaboration, M. Kherlakian The VERITAS Collaboration, D. Kieda The VERITAS Collaboration, T. K. Kleiner The VERITAS Collaboration, N. Korzoun The VERITAS Collaboration, S. Kumar The VERITAS Collaboration, M. J. Lang The VERITAS Collaboration, M. Lundy The VERITAS Collaboration, G. Maier The VERITAS Collaboration, C. E McGrath The VERITAS Collaboration, M. J. Millard The VERITAS Collaboration, J. Millis The VERITAS Collaboration, C. L. Mooney The VERITAS Collaboration, P. Moriarty The VERITAS Collaboration, R. Mukherjee The VERITAS Collaboration, S. O'Brien The VERITAS Collaboration, R. A. Ong The VERITAS Collaboration, M. Pohl The VERITAS Collaboration, E. Pueschel The VERITAS Collaboration, J. Quinn The VERITAS Collaboration, K. Ragan The VERITAS Collaboration, P. T. Reynolds The VERITAS Collaboration, D. Ribeiro The VERITAS Collaboration, E. Roache The VERITAS Collaboration, I. Sadeh The VERITAS Collaboration, A. C. Sadun The VERITAS Collaboration, L. Saha The VERITAS Collaboration, M. Santander The VERITAS Collaboration, G. H. Sembroski The VERITAS Collaboration, R. Shang The VERITAS Collaboration, M. Splettstoesser The VERITAS Collaboration, A. Kaushik Talluri The VERITAS Collaboration, J. V. Tucci The VERITAS Collaboration, V. V. Vassiliev The VERITAS Collaboration, A. Weinstein The VERITAS Collaboration, D. A. Williams The VERITAS Collaboration, S. L. Wong The VERITAS Collaboration, J. Woo The VERITAS Collaboration, F. Aharonian The H.E.S.S. Collaboration, J. Aschersleben The H.E.S.S. Collaboration, M. Backes The H.E.S.S. Collaboration, V. Barbosa Martins The H.E.S.S. Collaboration, R. Batzofin The H.E.S.S. Collaboration, Y. Becherini The H.E.S.S. Collaboration, D. Berge The H.E.S.S. Collaboration, K. Bernlohr The H.E.S.S. Collaboration, B. Bi The H.E.S.S. Collaboration, M. Bottcher The H.E.S.S. Collaboration, C. Boisson The H.E.S.S. Collaboration, J. Bolmont The H.E.S.S. Collaboration, M. de Bony de Lavergne The H.E.S.S. Collaboration, J. Borowska The H.E.S.S. Collaboration, M. Bouyahiaoui The H.E.S.S. Collaboration, F. Bradascio The H.E.S.S. Collaboration, M. Breuhaus The H.E.S.S. Collaboration, R. Brose The H.E.S.S. Collaboration, F. Brun The H.E.S.S. Collaboration, B. Bruno The H.E.S.S. Collaboration, T. Bulik The H.E.S.S. Collaboration, C. Burger-Scheidlin The H.E.S.S. Collaboration, S. Caroff The H.E.S.S. Collaboration, S. Casanova The H.E.S.S. Collaboration, R. Cecil The H.E.S.S. Collaboration, J. Celic The H.E.S.S. Collaboration, M. Cerruti The H.E.S.S. Collaboration, T. Chand The H.E.S.S. Collaboration, S. Chandra The H.E.S.S. Collaboration, A. Chen The H.E.S.S. Collaboration, J. Chibueze The H.E.S.S. Collaboration, O. Chibueze The H.E.S.S. Collaboration, G. Cotter The H.E.S.S. Collaboration, S. Dai The H.E.S.S. Collaboration, J. Damascene Mbarubucyeye The H.E.S.S. Collaboration, A. Djannati-Atai The H.E.S.S. Collaboration, A. Dmytriiev The H.E.S.S. Collaboration, V. Doroshenko The H.E.S.S. Collaboration, S. Einecke The H.E.S.S. Collaboration, J. -P. Ernenwein The H.E.S.S. Collaboration, G. Fichet de Clairfontaine The H.E.S.S. Collaboration, M. Filipovic The H.E.S.S. Collaboration, G. Fontaine The H.E.S.S. Collaboration, M. Fussling The H.E.S.S. Collaboration, S. Funk The H.E.S.S. Collaboration, S. Gabici The H.E.S.S. Collaboration, S. Ghafourizadeh The H.E.S.S. Collaboration, G. Giavitto The H.E.S.S. Collaboration, D. Glawion The H.E.S.S. Collaboration, J. F. Glicenstein The H.E.S.S. Collaboration, P. Goswami The H.E.S.S. Collaboration, G. Grolleron The H.E.S.S. Collaboration, L. Haerer The H.E.S.S. Collaboration, J. A. Hinton The H.E.S.S. Collaboration, T. L. Holch The H.E.S.S. Collaboration, M. Holler The H.E.S.S. Collaboration, D. Horns The H.E.S.S. Collaboration, M. Jamrozy The H.E.S.S. Collaboration, F. Jankowsky The H.E.S.S. Collaboration, V. Joshi The H.E.S.S. Collaboration, I. Jung-Richardt The H.E.S.S. Collaboration, E. Kasai The H.E.S.S. Collaboration, K. Katarzynski The H.E.S.S. Collaboration, R. Khatoon The H.E.S.S. Collaboration, B. Khelifi The H.E.S.S. Collaboration, S. Klepser The H.E.S.S. Collaboration, W. Kluzniak The H.E.S.S. Collaboration, K. Kosack The H.E.S.S. Collaboration, D. Kostunin The H.E.S.S. Collaboration, R. G. Lang The H.E.S.S. Collaboration, S. Le Stum The H.E.S.S. Collaboration, A. Lemiere The H.E.S.S. Collaboration, J. P. Lenain The H.E.S.S. Collaboration, F. Leuschner The H.E.S.S. Collaboration, T. Lohse The H.E.S.S. Collaboration, A. Luashvili The H.E.S.S. Collaboration, I. Lypova The H.E.S.S. Collaboration, J. Mackey The H.E.S.S. Collaboration, D. Malyshev The H.E.S.S. Collaboration, V. Marandon The H.E.S.S. Collaboration, P. Marchegiani The H.E.S.S. Collaboration, A. Marcowith The H.E.S.S. Collaboration, G. Marti-Devesa The H.E.S.S. Collaboration, R. Marx The H.E.S.S. Collaboration, A. Mitchell The H.E.S.S. Collaboration, R. Moderski The H.E.S.S. Collaboration, L. Mohrmann The H.E.S.S. Collaboration, A. Montanari The H.E.S.S. Collaboration, E. Moulin The H.E.S.S. Collaboration, T. Murach The H.E.S.S. Collaboration, K. Nakashima The H.E.S.S. Collaboration, J. Niemiec The H.E.S.S. Collaboration, A. Priyana Noel The H.E.S.S. Collaboration, P. O'Brien The H.E.S.S. Collaboration, L. Olivera-Nieto The H.E.S.S. Collaboration, E. de Ona Wilhelmi The H.E.S.S. Collaboration, M. Ostrowski The H.E.S.S. Collaboration, S. Panny The H.E.S.S. Collaboration, M. Panter The H.E.S.S. Collaboration, G. Peron The H.E.S.S. Collaboration, D. A. Prokhorov The H.E.S.S. Collaboration, G. Puhlhofer The H.E.S.S. Collaboration, M. Punch The H.E.S.S. Collaboration, A. Quirrenbach The H.E.S.S. Collaboration, P. Reichherzer The H.E.S.S. Collaboration, A. Reimer The H.E.S.S. Collaboration, O. Reimer The H.E.S.S. Collaboration, H. Ren The H.E.S.S. Collaboration, M. Renaud The H.E.S.S. Collaboration, F. Rieger The H.E.S.S. Collaboration, B. Rudak The H.E.S.S. Collaboration, E. Ruiz-Velasco The H.E.S.S. Collaboration, V. Sahakian The H.E.S.S. Collaboration, A. Santangelo The H.E.S.S. Collaboration, M. Sasaki The H.E.S.S. Collaboration, J. Schafer The H.E.S.S. Collaboration, F. Schussler The H.E.S.S. Collaboration, H. M. Schutte The H.E.S.S. Collaboration, U. Schwanke The H.E.S.S. Collaboration, J. N. S. Shapopi The H.E.S.S. Collaboration, A. Specovius The H.E.S.S. Collaboration, S. Spencer The H.E.S.S. Collaboration, L. Stawarz The H.E.S.S. Collaboration, R. Steenkamp The H.E.S.S. Collaboration, S. Steinmassl The H.E.S.S. Collaboration, I. Sushch The H.E.S.S. Collaboration, H. Suzuki The H.E.S.S. Collaboration, T. Takahashi The H.E.S.S. Collaboration, T. Tanaka The H.E.S.S. Collaboration, R. Terrier The H.E.S.S. Collaboration, C. van Eldik The H.E.S.S. Collaboration, M. Vecchi The H.E.S.S. Collaboration, J. Veh The H.E.S.S. Collaboration, C. Venter The H.E.S.S. Collaboration, J. Vink The H.E.S.S. Collaboration, R. White The H.E.S.S. Collaboration, A. Wierzcholska The H.E.S.S. Collaboration, Yu Wun Wong The H.E.S.S. Collaboration, M. Zacharias The H.E.S.S. Collaboration, D. Zargaryan The H.E.S.S. Collaboration, A. A. Zdziarski The H.E.S.S. Collaboration, A. Zech The H.E.S.S. Collaboration, S. Zouari The H.E.S.S. Collaboration, N. Zywucka The H.E.S.S. Collaboration, K. Mori

Abstract: We report on multiwavelength target-of-opportunity observations of the blazar PKS 0735+178, located 2.2$^\circ$ away from the best-fit position of the IceCube neutrino event IceCube-211208A detected on December 8, 2021. The source was in a high-flux state in the optical, ultraviolet, X-ray, and GeV gamma-ray bands around the time of the neutrino event, exhibiting daily variability in the soft X-ray flux. The X-ray data from Swift-XRT and NuSTAR characterize the transition between the low-energy and high-energy components of the broadband spectral energy distribution (SED), and the gamma-ray data from Fermi -LAT, VERITAS, and H.E.S.S. require a spectral cut-off near 100 GeV. Both X-ray and gamma-ray measurements provide strong constraints on the leptonic and hadronic models. We analytically explore a synchrotron self-Compton model, an external Compton model, and a lepto-hadronic model. Models that are entirely based on internal photon fields face serious difficulties in matching the observed SED. The existence of an external photon field in the source would instead explain the observed gamma-ray spectral cut-off in both leptonic and lepto-hadronic models and allow a proton jet power that marginally agrees with the Eddington limit in the lepto-hadronic model. We show a numerical lepto-hadronic model with external target photons that reproduces the observed SED and is reasonably consistent with the neutrino event despite requiring a high jet power.

Authors:Tom Broadhurst, Chao Chen, Tao Liu, Kai-Feng Zheng

Abstract: We explore the orbital implications of the Supermassive Black Hole (SMBH) binary in UGC4211, for the frequency spectrum of stochastic gravitational wave background (SGWB) being measured with pulsar timing arrays. The SMBH binary in UGC4211 has a projected separation of $\sim 230$ pc and relative velocity of $\sim 150$ km/s along the line of sight. It orbits a common disk of gas and stars, with a total dynamical mass of $\sim 10^9 M_\odot$ which is several times larger than the combined SMBHs plus the observed gas and stars. This can be explained by a massive soliton of wave dark matter present within the orbit of two SMBHs. Such a scenario is encouraging as during galaxy merger, the two precursor galactic solitons are expected to combine to generate a new soliton and hence the two initial SMBHs become efficiently bound. Generalizing this scenario to the cosmological population of SMBH binaries, we show that the SGWB spectrum produced by their late-stage inspiraling is modified preferentially at low frequency by the presence of the soliton. Finally we discuss future prospects for this proof-of-concept study, by fitting this scenario to the 15-year NANOGrav data.

Authors:Claudio Cremaschini, Massimo Tessarotto

Abstract: The problem posed by the possible existence/non-existence of spatially non-symmetric kinetic equilibria has remained unsolved in plasma theory. For collisionless magnetized plasmas this involves the construction of stationary solutions of the Vlasov-Maxwell equations. In this paper the issue is addressed for non-relativistic plasmas both in astrophysical and laboratory contexts. The treatment is based on a Lagrangian variational description of single-particle dynamics. Starting point is a non-perturbative formulation of gyrokinetic theory, which allows one to construct "a posteriori" with prescribed order of accuracy an asymptotic representation for the magnetic moment. In terms of the relevant particle adiabatic invariants generalized bi-Maxwellian equilibria are proved to exist. These are shown to recover, under suitable assumptions, a Chapman-Enskog form which permits an analytical treatment of the corresponding fluid moments. In particular, the constrained posed by the Poisson and the Ampere equations are analyzed, both for quasi-neutral and non-neutral plasmas. The conditions of existence of the corresponding non-symmetric kinetic equilibria are investigated. As a notable feature, both astrophysical and laboratory plasmas are shown to exhibit, under suitable conditions, a kinetic dynamo, whereby the equilibrium magnetic field can be self-generated by the equilibrium plasma currents.

Authors:Lei Zu, Chi Zhang, Yao-Yu Li, Yu-Chao Gu, Yue-Lin Sming Tsai, Yi-Zhong Fan

Abstract: Recent independent announcements by several collaborations have shown strong evidence of a Stochastic Gravitational-Wave Background (SGWB) detected through Pulsar Timing Arrays (PTAs). In this study, we investigate the implications of a first-order phase transition occurring within the early universe's dark quantum chromodynamics (dQCD) epoch, specifically within the framework of the mirror twin Higgs dark sector model. Our analysis indicates a distinguishable SGWB signal originating from this phase transition, which can explain the measurements obtained by PTAs. Remarkably, a significant portion of the parameter space within the mirror twin Higgs model that accounts for the SGWB signal also effectively resolves the existing tensions in both the $H_0$ and $S_8$ measurements in Cosmology. This intriguing correlation suggests a possible common origin for these three phenomena. Furthermore, the parameter region, $0.2 < \Delta N_{\rm eff} < 0.5$, where the mirror dark matter component constitutes less than $30\%$ of the total dark matter abundance, can accommodate all current cosmological observations and PTA measurements.

Authors:Xiao-Feng Cao, Wei-Wei Tan, Yun-Wei Yu, Zhen-Dong Zhang

Abstract: The nearest GRB 170817A provided an opportunity to probe the angular structure of the jet of this short gamma-ray burst (SGRB), by using its off-axis observed afterglow emission. It is investigated that whether the afterglow-constrained jet structures can be consistent with the luminosity of the prompt emission of GRB 170817A. Furthermore, by assuming that all SGRBs including GRB 170817A have the same explosive mechanism and jet structure, we apply the different jet structures into the calculation of the flux and redshfit distributions of the SGRB population, in comparison with the observational distributions of the Swift and Fermi sources. As a result, it is found that the single-Gaussian structure can be basically ruled out, whereas the power-law and two-Gaussian models can in principle survive.

Authors:Alisa Suray, Sergey Troitsky

Abstract: Radio blazars have been linked both to individual high-energy neutrino events and to excesses in likelihood sky maps constructed from lower-energy neutrino data. However, the exact mechanism by which neutrinos are produced in these sources is still unknown. Here, we demonstrate that IceCube neutrinos with energies over 200 TeV, which were previously associated with bright radio blazars, are significantly more likely to be accompanied by flares of lower-energy events, compared to those lacking blazar counterparts. The parsec-scale core radio flux of blazars positioned within the error regions of energetic events is strongly correlated with the likelihood of a coincident day-scale lower-energy neutrino flare reported by IceCube. The probability of a chance correlation is 3.6*10^{-4}. This confirms the neutrino-blazar connection in a new and independent way, and provides valuable clues to understanding the origin of astrophysical neutrinos.

Authors:Nektarios Vlahakis

Abstract: The stability of astrophysical jets in the linear regime is investigated by presenting the methodology to find the growth rates of the various instabilities. We perturb a cylindrical axisymmetric steady jet, linearize the relativistic ideal magnetohydrodynamic (MHD) equations, and analyze the evolution of the eigenmodes of the perturbation by deriving the differential equations that need to be integrated subject to the appropriate boundary conditions, in order to find the dispersion relation. We also apply the WKBJ approximation and additionally give analytical solutions in some subcases corresponding to unperturbed jets with constant bulk velocity along the symmetry axis.

Authors:Marvin Beck, Oindrila Ghosh, Florian Grüner, Martin Pohl, Carl B. Schroeder, Günter Sigl, Ryan D. Stark, Benno Zeitler

Abstract: Missing cascades from TeV blazar beams indicate that collective plasma effects may play a significant role in their energy loss. It is possible to mimic the evolution of such highly energetic pair beams in laboratory experiments using modern accelerators. The fate of the beam is governed by two different processes, energy loss through the unstable mode and energetic broadening of the pair beam through diffusion in momentum space. We chalk out this evolution using a Fokker-Planck approach in which the drift and the diffusion terms respectively describe these phenomena in a compact form. We present particle-in-cell simulations to trace the complete evolution of the unstable beam-plasma system for a generic narrow Gaussian pair beam for which the growth rate is reactive. We show that the instability leads to an energetic broadening of the pair beam, slowing down the instability growth in the linear phase, in line with the analytical and numerical solutions of the Fokker-Planck equation. Whereas in a laboratory experiment the change in the momentum distribution is an easily measured observable as a feedback of the instability, the consequence of diffusive broadening in an astrophysical scenario can be translated to an increase in the opening angle of the pair beam.

Authors:Gaetano Lambiase, Leonardo Mastrototaro, Luca Visinelli

Abstract: The pattern of neutrino flavor oscillations could be altered by the influence of noisy perturbations such as those arising from a gravitational wave background (GWB). A stochastic process that is consistent with a GWB has been recently reported by the independent analyses of pulsar timing array (PTA) data sets collected over a decadal timescale by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), the European Pulsar Timing Array (EPTA), the Parkes Pulsar Timing Array (PPTA), and the Chinese Pulsar Timing Array (CPTA) collaborations. We investigate the modifications in the neutrino flavor oscillations under the influence of the GWB reported by the PTA collaborations and we discuss how such effects could be potentially revealed in near-future neutrino detectors, possibly helping the discrimination of different models for the GWB below the nHz frequency range.

Authors:A. V. Glushkov, A. V. Sabourov, L. T. Ksenofontov, K. G. Lebedev

Abstract: Here we consider the results of direct measurements of muons in extensive air showers with zenith angles $\theta \le 45^{\circ}$ and energy above $10^{17}$ eV, obtained at the Pierre Auger Observatory and Yakutsk array. In both experiments muons were registered with underground scintillation detectors with $\approx 1.0 \times \sec\theta$ GeV energy threshold. Measured density values were compared to theoretical predictions calculated within the framework of the QGSJet-II.04 hadron interaction model. They differ by factor $1.53 \pm 0.13$(stat). We demonstrate that this difference is due to overestimation of muon densities by 1.22 times and underestimation of primary energy by 1.25 times in the Auger experiment.

Authors:Pierluca Carenza, Giampaolo Co', Maurizio Giannotti, Alessandro Lella, Giuseppe Lucente, Alessandro Mirizzi, Thomas Rauscher

Abstract: Axions coupled to nucleons might be copiously emitted from core-collapse supernovae (SNe). If the axion-nucleon coupling is strong enough, axions would be emitted from the SN as a burst and, reaching Earth, may excite the oxygen nuclei in water Cherenkov detectors (${}^{16}{\rm O} + a \to {}^{16}{\rm O}^{*}$). This process will be followed by radiative decay(s) of the excited state (${}^{16}{\rm O}^* \rightarrow {}^{16}{\rm O}+\gamma $) providing a strategy for a direct detection of axions from a Galactic SN in large underground neutrino Cherenkov detectors. Motivated by this possibility, we present an updated calculation of axion-oxygen cross section obtained by using self-consistent continuum Random Phase Approximation. We calculate the branching ratio of the oxygen nucleus de-excitation into gamma-rays, neutrons, protons and $\alpha$-particles. These results are used to revisit the detectability of axions from SN 1987A in Kamiokande-II.

Authors:M. J. Coe Southampton, J. A. Kennea PSU, I. M. Monageng UCT, D. A. H. Buckley SAAO, A. Udalski Warsaw, P. A. Evans Leicester

Abstract: Swift J0549.7-6812 is an Be/X-ray binary system (BeXRB) in the Large Magellanic Cloud (LMC) exhibiting a 6s pulse period. Like many such systems the variable X-ray emission is believed to be driven by the underlying behaviour of the mass donor Be star. In this paper we report on X-ray observations of the brightest known outburst from this system which reached a luminosity of 8 x 10^37 erg/s. These observations are supported by contemporaneous optical photometric observations, the first reported optical spectrum, as well as several years of historical data from OGLE and GAIA. The latter strongly suggest a binary period of 46.1d. All the observational data indicate that Swift J0549.7-6812 is a system that spends the vast majority of its time in X-ray quiescence, or even switched off completely. This suggests that occasional observations may easily miss it, and many similar systems, and thereby underestimate the massive star evolution numbers for the LMC.

Authors:Yaoyu Li, Chi Zhang, Ziwei Wang, Mingyang Cui, Yue-Lin Sming Tsai, Qiang Yuan, Yi-Zhong Fan

Abstract: The origin of interstellar and intergalactic magnetic fields is largely unknown, and the primordial magnetic fields (PMFs) produced by, e.g., phase transitions of the early Universe are expected to provide seeds for those magnetic fields. The PMFs affect the evolution of the Universe at an early time, resulting in a series of phenomena. In this work, we show that the PMF-induced turbulence can give rise to nanohertz (nHz) gravitational waves reported by several pulsar timing arrays, including NANOGrav, PPTA, EPTA, and CPTA. Using the nHz gravitational wave data, we obtain the constraints on the characteristic magnetic field strength ($B_{\rm ch}^* \sim \mathcal{O}(1)~\rm{\mu G}$) and coherent length scale ($\ell_{\rm ch}^* \sim \mathcal{O}(1)~\rm{pc}$) of PMFs, assuming a generation temperature of approximately the QCD temperature ($\sim 100$ MeV). In addition, the PMFs which evolve to the recombination era can induce baryon density inhomogeneities, and then alter the ionization process. This naturally results in an alleviation of the tension of the Hubble parameter $H_0$ and the matter clumpiness parameter $S_8$ between early and late-time measurements. Assuming an evolution form of $B_{\rm ch}\sim \ell_{\rm ch}^{-\alpha}$ from the epoch of the production of PMFs to the epoch of recombination, we find $0.91<\alpha<1.08$ (95\% credible region).

Authors:Zhao-Qiang Shen, Guan-Wen Yuan, Yi-Ying Wang, Yuan-Zhu Wang

Abstract: Recently, the NANOGrav, PPTA, EPTA and CPTA collaborations reported compelling evidence of the existence of the Stochastic Gravitational-Wave Background (SGWB). The amplitude and spectrum of this inferred gravitational-wave background align closely with the astrophysical predictions for a signal originating from the population of supermassive black-hole binaries. In light of these findings, we explore the possibility to detect dark matter spikes surrounding massive black holes, which could potentially impact the gravitational-wave waveform and modulate the SGWB. We demonstrate that the SMBH binary evolution induced by the combined effects of GW radiation and the dynamical friction of the dark matter spike exhibits detectable manifestations within the nHz frequency range of the SGWB.

Authors:Ziwei Wang, Lei Lei, Hao Jiao, Lei Feng, Yi-Zhong Fan

Abstract: Very recently, the Pulsar Timing Array (PTA) experiments reported strong evidence for the presence of the nanohertz stochastic gravitational wave background (SGWB). In this work we show that the cosmic string loops can account for the nanohertz SGWB data with a $G\mu \sim 2\times 10^{-12}$ and the loops number density $N \sim 10^{4}$. Though the presence of cosmic string loops can also effectively enhance the number density of massive galaxies at high redshifts, we do not find a reasonable parameter space to self-consistently interpret both the SGWB data and the JWST observations. This implies either an extension of the model adopted in this work or the different physical origins of these two phenomena.

Authors:Qingchang Zhao, Hongxing Yin, Lian Tao, Zixu Yang, Jinlu Qu, Liang Zhang, Shu Zhang, Erlin Qiao, Qingcui Bu, Shujie Zhao, Panping Li, Yiming Huang, Ruican Ma, Ruijing Tang, Pei Jin, Wei Yu, Hexin Liu, Yue Huang, Xiang Ma, Jingyu Xiao, Xuan Zhang, Kang Zhao

Abstract: We present the results of a detailed timing and spectral analysis of the quasi-regular modulation (QRM) phenomenon in the black hole X-ray binary 4U 1630--47 during its 1998 outburst observed by Rossi X-ray Timing Explore (RXTE). We find that the $\sim$ 50-110 mHz QRM is flux dependent, and the QRM is detected with simultaneous low frequency quasi-periodic oscillations (LFQPOs). According to the behavior of the power density spectrum, we divide the observations into four groups. In the first group, namely behavior A, LFQPOs are detected, but no mHz QRM. The second group, namely behavior B, a QRM with frequency above $\sim$ 88 mHz is detected and the $\sim$ 5 Hz and $\sim$ 7 Hz LFQPOs are almost overlapping. In the third group, namely behavior C, the QRM frequency below $\sim$ 88 mHz is detected and the LFQPOs are significantly separated. In the forth group, namely behavior D, neither QRM nor LFQPOs are detected. We study the energy-dependence of the fractional rms, centroid frequency, and phase-lag of QRM and LFQPOs for behavior B and C. We then study the evolution of QRM and find that the frequency of QRM increases with hardness, while its rms decreases with hardness. We also analyze the spectra of each observation, and find that the QRM rms of behavior B has a positive correlation with $\rm F_{\rm powerlaw}$ / $\rm F_{\rm total}$. Finally, we give our understanding for this mHz QRM phenomena.

Authors:Claudio Cremaschini, Massimo Tessarotto

Abstract: This paper is concerned with the kinetic treatment of quasi-stationary axisymmetric collisionless accretion disc plasmas. The conditions of validity of the kinetic description for non-relativistic magnetized and gravitationally-bound plasmas of this type are discussed. A classification of the possible collisionless plasma regimes which can arise in these systems is proposed, which can apply to accretion discs around both stellar-mass compact objects and galactic-center black holes. Two different classifications are determined, which are referred to respectively as energy-based and magnetic field-based classifications. Different regimes are pointed out for each plasma species, depending both on the relative magnitudes of kinetic and potential energies and the magnitude of the magnetic field. It is shown that in all cases, there can be quasi-stationary Maxwellian-like solutions of the Vlasov equation. The perturbative approach outlined here permits unique analytical determination of the functional form for the distribution function consistent, in each kinetic regime, with the explicit inclusion of finite Larmor radius-diamagnetic and/or energy-correction effects.

Authors:Shin'ichiro Ando, Nick Ekanger, Shunsaku Horiuchi, Yusuke Koshio

Abstract: Core-collapse supernovae are among the most powerful explosions in the universe, emitting thermal neutrinos that carry away the majority of the gravitational binding energy released. These neutrinos create a diffuse supernova neutrino background (DSNB), one of the largest energy budgets among all radiation backgrounds. Detecting the DSNB is a crucial goal of modern high-energy astrophysics and particle physics, providing valuable insights in both core-collapse modeling, neutrino physics, and cosmic supernova rate history. In this review, we discuss the key ingredients of DSNB calculation and what we can learn from future detections, including black-hole formation and non-standard neutrino interactions. Additionally, we provide an overview of the latest updates in neutrino experiments, which could lead to the detection of the DSNB in the next decade. With the promise of this breakthrough discovery on the horizon, the study of DSNB holds enormous potential for advancing our understanding of the Universe.

Authors:Constantin Steppa, Kathrin Egberts

Abstract: As an observer from within the Milky Way, it is difficult to determine its global structure. Despite extensive observational data from surveys at different wavelengths, we have no conclusive description of the structure of our own Galaxy. For very-high-energy (VHE) $\gamma$ rays, the most comprehensive catalogue of Galactic sources resulting from the H.E.S.S. Galactic Plane Survey (HGPS) shows a striking asymmetry in the distribution of the sources in the latitudinal direction. This could be the result of a local feature in the spatial distribution of the sources or it could be due to the position of the Sun above the Galactic plane. In this contribution, we estimate the position of the Sun based on the latitudinal flux profile of VHE $\gamma$-ray sources, assuming three mirror-symmetric models for the spatial distribution of the sources in three-dimensional space and taking into account the observational bias of the HGPS. We verify our method using simulations and find values for $z_{\odot}$ between $-6\,\mathrm{pc}$ and $94\,\mathrm{pc}$ depending on the considered model. Our results show that the position of the Sun has a significant impact on the observed source distribution and must therefore be taken into account when modelling the population of Galactic VHE $\gamma$ sources. However, it is not conclusive whether the Sun's offset from the Galactic plane is the only factor leading to the asymmetry in the latitudinal profile.

Authors:Gabriella Agazie The NANOGrav Collaboration, Akash Anumarlapudi The NANOGrav Collaboration, Anne M. Archibald The NANOGrav Collaboration, Zaven Arzoumanian The NANOGrav Collaboration, Paul T. Baker The NANOGrav Collaboration, Bence Becsy The NANOGrav Collaboration, Laura Blecha The NANOGrav Collaboration, Adam Brazier The NANOGrav Collaboration, Paul R. Brook The NANOGrav Collaboration, Sarah Burke-Spolaor The NANOGrav Collaboration, Rand Burnette The NANOGrav Collaboration, Robin Case The NANOGrav Collaboration, Maria Charisi The NANOGrav Collaboration, Shami Chatterjee The NANOGrav Collaboration, Katerina Chatziioannou The NANOGrav Collaboration, Belinda D. Cheeseboro The NANOGrav Collaboration, Siyuan Chen The NANOGrav Collaboration, Tyler Cohen The NANOGrav Collaboration, James M. Cordes The NANOGrav Collaboration, Neil J. Cornish The NANOGrav Collaboration, Fronefield Crawford The NANOGrav Collaboration, H. Thankful Cromartie The NANOGrav Collaboration, Kathryn Crowter The NANOGrav Collaboration, Curt J. Cutler The NANOGrav Collaboration, Megan E. DeCesar The NANOGrav Collaboration, Dallas DeGan The NANOGrav Collaboration, Paul B. Demorest The NANOGrav Collaboration, Heling Deng The NANOGrav Collaboration, Timothy Dolch The NANOGrav Collaboration, Brendan Drachler The NANOGrav Collaboration, Justin A. Ellis The NANOGrav Collaboration, Elizabeth C. Ferrara The NANOGrav Collaboration, William Fiore The NANOGrav Collaboration, Emmanuel Fonseca The NANOGrav Collaboration, Gabriel E. Freedman The NANOGrav Collaboration, Nate Garver-Daniels The NANOGrav Collaboration, Peter A. Gentile The NANOGrav Collaboration, Kyle A. Gersbach The NANOGrav Collaboration, Joseph Glaser The NANOGrav Collaboration, Deborah C. Good The NANOGrav Collaboration, Kayhan Gultekin The NANOGrav Collaboration, Jeffrey S. Hazboun The NANOGrav Collaboration, Sophie Hourihane The NANOGrav Collaboration, Kristina Islo The NANOGrav Collaboration, Ross J. Jennings The NANOGrav Collaboration, Aaron D. Johnson The NANOGrav Collaboration, Megan L. Jones The NANOGrav Collaboration, Andrew R. Kaiser The NANOGrav Collaboration, David L. Kaplan The NANOGrav Collaboration, Luke Zoltan Kelley The NANOGrav Collaboration, Matthew Kerr The NANOGrav Collaboration, Joey S. Key The NANOGrav Collaboration, Tonia C. Klein The NANOGrav Collaboration, Nima Laal The NANOGrav Collaboration, Michael T. Lam The NANOGrav Collaboration, William G. Lamb The NANOGrav Collaboration, T. Joseph W. Lazio The NANOGrav Collaboration, Natalia Lewandowska The NANOGrav Collaboration, Tyson B. Littenberg The NANOGrav Collaboration, Tingting Liu The NANOGrav Collaboration, Andrea Lommen The NANOGrav Collaboration, Duncan R. Lorimer The NANOGrav Collaboration, Jing Luo The NANOGrav Collaboration, Ryan S. Lynch The NANOGrav Collaboration, Chung-Pei Ma The NANOGrav Collaboration, Dustin R. Madison The NANOGrav Collaboration, Margaret A. Mattson The NANOGrav Collaboration, Alexander McEwen The NANOGrav Collaboration, James W. McKee The NANOGrav Collaboration, Maura A. McLaughlin The NANOGrav Collaboration, Natasha McMann The NANOGrav Collaboration, Bradley W. Meyers The NANOGrav Collaboration, Patrick M. Meyers The NANOGrav Collaboration, Chiara M. F. Mingarelli The NANOGrav Collaboration, Andrea Mitridate The NANOGrav Collaboration, Priyamvada Natarajan The NANOGrav Collaboration, Cherry Ng The NANOGrav Collaboration, David J. Nice The NANOGrav Collaboration, Stella Koch Ocker The NANOGrav Collaboration, Ken D. Olum The NANOGrav Collaboration, Timothy T. Pennucci The NANOGrav Collaboration, Benetge B. P. Perera The NANOGrav Collaboration, Polina Petrov The NANOGrav Collaboration, Nihan S. Pol The NANOGrav Collaboration, Henri A. Radovan The NANOGrav Collaboration, Scott M. Ransom The NANOGrav Collaboration, Paul S. Ray The NANOGrav Collaboration, Joseph D. Romano The NANOGrav Collaboration, Shashwat C. Sardesai The NANOGrav Collaboration, Ann Schmiedekamp The NANOGrav Collaboration, Carl Schmiedekamp The NANOGrav Collaboration, Kai Schmitz The NANOGrav Collaboration, Levi Schult The NANOGrav Collaboration, Brent J. Shapiro-Albert The NANOGrav Collaboration, Xavier Siemens The NANOGrav Collaboration, Joseph Simon The NANOGrav Collaboration, Magdalena S. Siwek The NANOGrav Collaboration, Ingrid H. Stairs The NANOGrav Collaboration, Daniel R. Stinebring The NANOGrav Collaboration, Kevin Stovall The NANOGrav Collaboration, Jerry P. Sun The NANOGrav Collaboration, Abhimanyu Susobhanan The NANOGrav Collaboration, Joseph K. Swiggum The NANOGrav Collaboration, Jacob Taylor The NANOGrav Collaboration, Stephen R. Taylor The NANOGrav Collaboration, Jacob E. Turner The NANOGrav Collaboration, Caner Unal The NANOGrav Collaboration, Michele Vallisneri The NANOGrav Collaboration, Rutger van Haasteren The NANOGrav Collaboration, Sarah J. Vigeland The NANOGrav Collaboration, Haley M. Wahl The NANOGrav Collaboration, Qiaohong Wang The NANOGrav Collaboration, Caitlin A. Witt The NANOGrav Collaboration, Olivia Young The NANOGrav Collaboration

Abstract: We report multiple lines of evidence for a stochastic signal that is correlated among 67 pulsars from the 15-year pulsar-timing data set collected by the North American Nanohertz Observatory for Gravitational Waves. The correlations follow the Hellings-Downs pattern expected for a stochastic gravitational-wave background. The presence of such a gravitational-wave background with a power-law-spectrum is favored over a model with only independent pulsar noises with a Bayes factor in excess of $10^{14}$, and this same model is favored over an uncorrelated common power-law-spectrum model with Bayes factors of 200-1000, depending on spectral modeling choices. We have built a statistical background distribution for these latter Bayes factors using a method that removes inter-pulsar correlations from our data set, finding $p = 10^{-3}$ (approx. $3\sigma$) for the observed Bayes factors in the null no-correlation scenario. A frequentist test statistic built directly as a weighted sum of inter-pulsar correlations yields $p = 5 \times 10^{-5} - 1.9 \times 10^{-4}$ (approx. $3.5 - 4\sigma$). Assuming a fiducial $f^{-2/3}$ characteristic-strain spectrum, as appropriate for an ensemble of binary supermassive black-hole inspirals, the strain amplitude is $2.4^{+0.7}_{-0.6} \times 10^{-15}$ (median + 90% credible interval) at a reference frequency of 1/(1 yr). The inferred gravitational-wave background amplitude and spectrum are consistent with astrophysical expectations for a signal from a population of supermassive black-hole binaries, although more exotic cosmological and astrophysical sources cannot be excluded. The observation of Hellings-Downs correlations points to the gravitational-wave origin of this signal.

Authors:J. Antoniadis, P. Arumugam, S. Arumugam, S. Babak, M. Bagchi, A. -S. Bak Nielsen, C. G. Bassa, A. Bathula, A. Berthereau, M. Bonetti, E. Bortolas, P. R. Brook, M. Burgay, R. N. Caballero, A. Chalumeau, D. J. Champion, S. Chanlaridis, S. Chen, I. Cognard, S. Dandapat, D. Deb, S. Desai, G. Desvignes, N. Dhanda-Batra, C. Dwivedi, M. Falxa, R. D. Ferdman, A. Franchini, J. R. Gair, B. Goncharov, A. Gopakumar, E. Graikou, J. -M. Grießmeier, L. Guillemot, Y. J. Guo, Y. Gupta, S. Hisano, H. Hu, F. Iraci, D. Izquierdo-Villalba, J. Jang, J. Jawor, G. H. Janssen, A. Jessner, B. C. Joshi, F. Kareem, R. Karuppusamy, E. F. Keane, M. J. Keith, D. Kharbanda, T. Kikunaga, N. Kolhe, M. Kramer, M. A. Krishnakumar, K. Lackeos, K. J. Lee, K. Liu, Y. Liu, A. G. Lyne, J. W. McKee, Y. Maan, R. A. Main, M. B. Mickaliger, I. C. Nitu, K. Nobleson, A. K. Paladi, A. Parthasarathy, B. B. P. Perera, D. Perrodin, A. Petiteau, N. K. Porayko, A. Possenti, T. Prabu, H. Quelquejay Leclere, P. Rana, A. Samajdar, S. A. Sanidas, A. Sesana, G. Shaifullah, J. Singha, L. Speri, R. Spiewak, A. Srivastava, B. W. Stappers, M. Surnis, S. C. Susarla, A. Susobhanan, K. Takahashi, P. Tarafdar, G. Theureau, C. Tiburzi, E. van der Wateren, A. Vecchio, V. Venkatraman Krishnan, J. P. W. Verbiest, J. Wang, L. Wang, Z. Wu

Abstract: We present the results of the search for an isotropic stochastic gravitational wave background (GWB) at nanohertz frequencies using the second data release of the European Pulsar Timing Array (EPTA) for 25 millisecond pulsars and a combination with the first data release of the Indian Pulsar Timing Array (InPTA). We analysed (i) the full 24.7-year EPTA data set, (ii) its 10.3-year subset based on modern observing systems, (iii) the combination of the full data set with the first data release of the InPTA for ten commonly timed millisecond pulsars, and (iv) the combination of the 10.3-year subset with the InPTA data. These combinations allowed us to probe the contributions of instrumental noise and interstellar propagation effects. With the full data set, we find marginal evidence for a GWB, with a Bayes factor of four and a false alarm probability of $4\%$. With the 10.3-year subset, we report evidence for a GWB, with a Bayes factor of $60$ and a false alarm probability of about $0.1\%$ ($\gtrsim 3\sigma$ significance). The addition of the InPTA data yields results that are broadly consistent with the EPTA-only data sets, with the benefit of better noise modelling. Analyses were performed with different data processing pipelines to test the consistency of the results from independent software packages. The inferred spectrum from the latest EPTA data from new generation observing systems is rather uncertain and in mild tension with the common signal measured in the full data set. However, if the spectral index is fixed at 13/3, the two data sets give a similar amplitude of ($2.5\pm0.7)\times10^{-15}$ at a reference frequency of $1\,{\rm yr}^{-1}$. By continuing our detection efforts as part of the International Pulsar Timing Array (IPTA), we expect to be able to improve the measurement of spatial correlations and better characterise this signal in the coming years.

Authors:Daniel J. Reardon, Andrew Zic, Ryan M. Shannon, George B. Hobbs, Matthew Bailes, Valentina Di Marco, Agastya Kapur, Axl F. Rogers, Eric Thrane, Jacob Askew, N. D. Ramesh Bhat, Andrew Cameron, Małgorzata Curyło, William A. Coles, Shi Dai, Boris Goncharov, Matthew Kerr, Atharva Kulkarni, Yuri Levin, Marcus E. Lower, Richard N. Manchester, Rami Mandow, Matthew T. Miles, Rowina S. Nathan, Stefan Osłowski, Christopher J. Russell, Renée Spiewak, Songbo Zhang, Xing-Jiang Zhu

Abstract: Pulsar timing arrays aim to detect nanohertz-frequency gravitational waves (GWs). A background of GWs modulates pulsar arrival times and manifests as a stochastic process, common to all pulsars, with a signature spatial correlation. Here we describe a search for an isotropic stochastic gravitational-wave background (GWB) using observations of 30 millisecond pulsars from the third data release of the Parkes Pulsar Timing Array (PPTA), which spans 18 years. Using current Bayesian inference techniques we recover and characterize a common-spectrum noise process. Represented as a strain spectrum $h_c = A(f/1 {\rm yr}^{-1})^{\alpha}$, we measure $A=3.1^{+1.3}_{-0.9} \times 10^{-15}$ and $\alpha=-0.45 \pm 0.20$ respectively (median and 68% credible interval). For a spectral index of $\alpha=-2/3$, corresponding to an isotropic background of GWs radiated by inspiraling supermassive black hole binaries, we recover an amplitude of $A=2.04^{+0.25}_{-0.22} \times 10^{-15}$. However, we demonstrate that the apparent signal strength is time-dependent, as the first half of our data set can be used to place an upper limit on $A$ that is in tension with the inferred common-spectrum amplitude using the complete data set. We search for spatial correlations in the observations by hierarchically analyzing individual pulsar pairs, which also allows for significance validation through randomizing pulsar positions on the sky. For a process with $\alpha=-2/3$, we measure spatial correlations consistent with a GWB, with an estimated false-alarm probability of $p \lesssim 0.02$ (approx. $2\sigma$). The long timing baselines of the PPTA and the access to southern pulsars will continue to play an important role in the International Pulsar Timing Array.