High Energy Astrophysical Phenomena (astro-ph.HE)

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.

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.

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.

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.

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.

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.

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.