SN 2021wuf: A transitional type Ia supernova with a low-velocity gradient

¹ Center for Astronomy and Space Sciences, China Three Gorges University, Yichang 443000, People’s Republic of China
² College of Science, 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
⁸ School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China
⁹ Yunnan Observatories (YNAO), Chinese Academy of Sciences, Kunming 650216, People’s Republic of China
¹⁰ Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, Kunming 650216, People’s Republic of China
¹¹ Center for Astronomical Mega-Science, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100012, People’s Republic of China
¹² Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, People’s Republic of China
¹³ George P. and Cynthia Woods Mitchell Institute for Fundamental Physics & Astronomy, Texas A&M University, Department of Physics and Astronomy, 4242 TAMU, College Station, TX 77843, USA
¹⁴ Shanghai Key Lab for Astrophysics, Shanghai Normal University, Shanghai 200234, People’s Republic of China

^⋆ Corresponding authors; wang_xf@mail.tsinghua.edu.cn, zsh@ctgu.edu.cn

Received: 10 June 2024
Accepted: 30 August 2024

Abstract

In this paper, we present an extensive analysis of SN 2021 wuf, a transition between Ia-norm and SN 1991T-like supernovae, which exploded at the periphery of the tidal bridge between the pair galaxy NGC 6500 and NGC 6501, at a redshift of z = 0.01. Our observations, ranging from −21 to +276 days relative to the B-band maximum light, reveal that SN 2021wuf exhibits properties akin to normal SNe Ia, with a peak absolute magnitude of M_max(B)  ∼   − 19.49  ±  0.10 mag and a post-peak decline rate of Δm₁₅(B)  ∼  1.11  ±  0.06 mag. The peak bolometric luminosity of this SN is estimated as 1.58  × 10⁴³ erg s⁻¹, corresponding to a ⁵⁶Ni mass of M_Ni  ∼  0.64  ±  0.05 M_⊙. The spectral features, including high-velocity Si IIλ6355 lines, a plateau in the Si IIλ6355 velocity evolution and the nickel-to-iron ratio in the nebular phase, suggest a potential pulsating delayed detonation mechanism. The absence of intermediate-mass elements in the early phase and the high photospheric temperature, as inferred from the line-strength ratio of Si IIλ5972 to Si IIλ6355 (named as R(Si II)), further support this classification.