SN 2023xqm: A gradually fading Ia supernova exhibiting isolated high-velocity signatures

¹ Center for Astronomy and Space Sciences, China Three Gorges University, Yichang 443000, People’s Republic of China
² College of Mathematics and Physics, China Three Gorges University, Yichang 443000, People’s Republic of China
³ Beijing Planetarium, Beijing Academy of Science of Technology, Beijing 100044, People’s Republic of China
⁴ Physics Department and Tsinghua Center for Astrophysics (THCA), Tsinghua University, Beijing 100084, People’s Republic of China
⁵ Department of Physics, University of California, Santa Barbara, CA 93106-9530, USA
⁶ Las Cumbres Observatory, 6740 Cortona Drive Suite 102, Goleta, CA 93117-5575, USA
⁷ Xinjiang Astronomical Observatory, Chinese Academy of Sciences, Urumqi, Xinjiang 830011, People’s Republic of China

^⋆ Corresponding authors: wangxf@mail.tsinghua.edu.cn, zsh@ctgu.edu.cn

Received: 4 November 2024
Accepted: 10 April 2025

Abstract

We conducted an exhaustive analysis combining optical photometry and spectroscopy of the type Ia supernova designated SN 2023xqm. Our observational period spanned from the two weeks preceding to 88 days after the B-band peak luminosity time. We determined the peak brightness in the B-band to be −18.90 ± 0.50 mag, and it is accompanied by a moderately slow decay rate of 0.90 ± 0.07 mag. The maximum quasi-bolometric luminosity was estimated to be 1.52 × 10⁴³ erg s⁻¹ and correlated with a calculated ⁵⁶Ni mass of 0.74 ± 0.05 M_⊙, aligning with the modestly reduced rate of light curve decay. A plateau that can be observed in the r − i color curve might correlate with the minor elevation noted between the principal and secondary peaks of the i-band light curve. An initial spectral analysis of SN 2023xqm revealed distinct high-velocity features (HVFs) in Ca II that contrast with the subdued HVFs observed in Si II. Such attributes may stem from variations in ionization or temperature or from scenarios involving enhanced element abundance, suggesting a naturally lower photospheric temperature for SN 2023xqm, which could be indicative of incomplete burning during the white dwarf’s detonation. The observed traits in the light curve and the spectral features offer significant insights into the variability among type Ia supernovae and their explosion dynamics.