2026ApJ...996...10L

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 ± 0.29 mag and subsequently declines by Δm₁₅(B) ≈ 1.12 mag, consistent with the luminosity-width relation characteristic of normal SNe Ia. Based on the peak thermal luminosity of (1.2 ± 0.3) × 10⁴³ erg s^–1, we estimate that 0.57 ± 0.14 M_⊙ of ⁵⁶Ni was synthesized during the explosion. Our dense early spectral monitoring revealed significant velocity disparities within the ejecta. Notably, absorption features from the Ca II near-infrared triplet were observed at velocities exceeding 25,000 km s^–1, while the Si IIλ6355 line velocity at the same epoch was significantly lower at ∼16,000 km s^–1. This velocity disparity likely reflects distinct ionization states of intermediate-mass elements in the outermost layers. The prominent Ca II 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.