Liping Li, Zhenyu Wang, Jialian Liu, Yu Pan, Alexei V. Filippenko, Jujia Zhang, Xiaofeng Wang, Brajesh Kumar, Yi Yang, Thomas G. Brink, WeiKang Zheng, Xiangcun Meng, Lingzhi Wang, Zeyi Zhao, Qian Zhai, Yongzhi Cai, Giuliano Pignata, Xinlei Chen, Xingzhu Zou, Jiewei Zhao, Xiangkun Liu, Xiaowei Liu, Xinzhong Er, A. Reguitti, R. Michael Rich, Jon M. Rees, Mark A. Croom, K. Itagaki, Bo Wang, Jinming Bai

We present photometric and spectroscopic observations of SN 2024gy, a Type Ia supernova (SN Ia) exhibiting high-velocity features (HVFs) in its early-time spectra. This SN reaches a peak $B$-band magnitude of $-19.25 \pm 0.28$ mag and subsequently declines by $\Delta m_{15}(B) \approx 1.12$ mag, consistent with the luminosity-width relation characteristic of normal SNe Ia. Based on the peak thermal luminosity of $(1.2 \pm 0.3) \times 10^{43}$ erg s$^{-1}$, we estimate that $0.57 \pm 0.14~\rm M_{\odot}$ of $^{56}$Ni was synthesized during the explosion. Our dense early spectral monitoring revealed significant velocity disparities within the ejecta. Notably, absorption features from the \CaII\ near-infrared triplet were observed at velocities exceeding 25,000 km s$^{-1}$, while the \SiII\, \ld 6355 line velocity at the same epoch was significantly lower at $\sim$ 16,000 km s$^{-1}$. This velocity disparity likely reflects distinct ionization states of intermediate-mass elements in the outermost layers. The prominent \CaII\, HVFs may originate from ionization suppression within the highest-velocity ejecta, potentially indicative of minimal hydrogen mixing in a delayed-detonation explosion scenario. Additionally, the Ni/Fe ratio derived from the nebular spectrum of SN 2024gy provides further support for this model.