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

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 Δ m 15 ( B ) ∼ 1.11 ± 0.06 mag. The peak bolometric luminosity of this SN is estimated as 1.58 × 10 43 erg s −1 , corresponding to a 56 Ni mass of M Ni ∼ 0.64 ± 0.05 M ⊙ . The spectral features, including high-velocity Si II λ 6355 lines, a plateau in the Si II λ 6355 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 II λ 5972 to Si II λ 6355 (named as R (Si II )), further support this classification.