Helium Superluminous SN 2021bnw: An Explosion of a Massive Star with a Preoutburst

This is the authors' abstract. We don't add key points for this paper.

Superluminous supernovae (SLSNe) remain an intriguing topic in supernova (SN) transient astronomy. While the majority of SLSNe are shown to be explained by energy streaming from the newly born magnetar, there are others that are powered by different mechanisms. We analyse the pseudobolometric light curve of the nearby helium-rich SLSN 2021bnw. We build models and run hydrodynamics radiative-transfer simulations with STELLA . Our best-fit models include 15–22.5 M ⊙ of ejecta enriched with 1.7 M ⊙ of 56 Ni, carrying an energy of 4 foe (1 foe ≡ 10 51 erg) and colliding with 7 M ⊙ of circumstellar matter, which matches the observed light curve very well. The early data can be explained as cooling of an expanding shell with the mass of 0.5 M ⊙ and the kinetic energy of 0.7 foe. We tend to exclude a pulsational pair-instability origin for SLSN 2021bnw. Instead we conclude that SLSN 2021bnw was preferably a core-collapse explosion of a star with the initial mass no less than 61 M ⊙ , aided by magnetorotational effects.