2026/07/20 by Liping Li, Jujia Zhang, Zhenyu Wang +5
#astro-ph.HE #astro-ph.SR
We present optical observations on the young type Ia supernova (SN Ia) SN 2021fxy obtained within a few days after the explosion, with a focus on its prominent high-velocity features (HVFs). It reached a B-band maximum of M\rm max(B) = -19.36±0.31 mag, corresponding to a bolometric luminosity of ∼ 1.3×1043~\rmerg~s-1 with a synthesized 56Ni mass of 0.58±0.14 M\odot. The early spectra exhibit strong HVFs of intermediate-mass elements that are significantly detached from the photospheric components. In particular, the velocity of the Si II λ6355 HVFs follows a power-law evolution (β≈ 0.1), shallower than the expected photospheric velocity evolution expected for an assumed n=10 density profile (β≈ 0.22) under homologous expansion. This behavior is consistent with the HVFs forming in intrinsic ejecta structures at least partially decoupled from the bulk outer ejecta, providing a possible constraint on the explosion physics of SNe Ia.