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Helium superluminous SN 2021bnw : an explosion of a massive star with a pre-outburst

Alexandra Kozyreva, Matteo Bugli, Alexey Mironov, Petr Baklanov

TL;DR

This study investigates the powering mechanism of the helium-rich SLSN 2021bnw by combining SN ejecta--CSM interaction with radioactive decay of ${}^{56}$Ni, using STELLAR radiative-transfer simulations. The authors find best-fit parameters with $M_{ej} obreak= obreak 15$–$22.5$ Msun, $M_{CSM} obreak= obreak 6.6$–$7.6$ Msun, $M_{{}^{56}{ m Ni}} obreak= obreak 1.7$ Msun, and $E_{kin} obreak oughly obreak 4$ foe, plus a pre-SN shell of $M_{shell} obreak = obreak 0.5$–1 Msun and $E_k obreak= obreak 0.7$–1 foe to explain the early data. The inferred progenitor was a very massive star with $M_{ZAMS} obreak ext{(} obreak obreak M_ ext{ZAMS} obreak) obreak ext{>} obreak 61$ Msun, likely undergoing magnetorotational core-collapse rather than a PPISN. The results suggest that He-rich SLSNe can arise from magnetorotational explosions in very massive stars with substantial CSM interaction, aided by a pre-explosion outburst, with implications for the endpoints of the most massive stars and the diversity of SLSN light curves.

Abstract

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 which are powered by different mechanisms. We analyse the pseudo-bolometric light curve of the nearby helium-rich SLSN 2021bnw. We built models and run hydrodynamics radiative-transfer simulations with STELLA. Our best-fit models include 15-22.5 Msun of ejecta enriched with 1.7 Msun of 56 Ni and carrying energy of 4 foe, and colliding w ith 7 Msun of circumstellar matter which match the observed light curve very well. The early data can be explained as cooling of an expanding shell with the mass of 0.5 Msun and kinetic energy of 0.7 foe. We tend to exclude a pulsational pair-instability (PPISN) origin for SLSN 2021bnw. Instead we conclude that SLSN 2021bnw was preferably a core-collapse explosion of a star with the initial mass of not less than 61 Msun aided by magnetorotational effects.

Helium superluminous SN 2021bnw : an explosion of a massive star with a pre-outburst

TL;DR

This study investigates the powering mechanism of the helium-rich SLSN 2021bnw by combining SN ejecta--CSM interaction with radioactive decay of Ni, using STELLAR radiative-transfer simulations. The authors find best-fit parameters with – Msun, – Msun, Msun, and foe, plus a pre-SN shell of –1 Msun and –1 foe to explain the early data. The inferred progenitor was a very massive star with Msun, likely undergoing magnetorotational core-collapse rather than a PPISN. The results suggest that He-rich SLSNe can arise from magnetorotational explosions in very massive stars with substantial CSM interaction, aided by a pre-explosion outburst, with implications for the endpoints of the most massive stars and the diversity of SLSN light curves.

Abstract

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 which are powered by different mechanisms. We analyse the pseudo-bolometric light curve of the nearby helium-rich SLSN 2021bnw. We built models and run hydrodynamics radiative-transfer simulations with STELLA. Our best-fit models include 15-22.5 Msun of ejecta enriched with 1.7 Msun of 56 Ni and carrying energy of 4 foe, and colliding w ith 7 Msun of circumstellar matter which match the observed light curve very well. The early data can be explained as cooling of an expanding shell with the mass of 0.5 Msun and kinetic energy of 0.7 foe. We tend to exclude a pulsational pair-instability (PPISN) origin for SLSN 2021bnw. Instead we conclude that SLSN 2021bnw was preferably a core-collapse explosion of a star with the initial mass of not less than 61 Msun aided by magnetorotational effects.
Paper Structure (8 sections, 2 figures)

This paper contains 8 sections, 2 figures.

Table of Contents

  1. Introduction
  2. Light curve modeling: two main powering contributors
  3. Results: SN ejecta -- CSM interaction and radioactive nickel as a working model for SN 2021bnw LC
  4. Evolutionary path to the eruption and explosion that led to SN 2021bnw
  5. The initial mass of a progenitor of SN 2021bnw
  6. Can SN 2021bnw be a PPISN?
  7. The origin of CSM and the pre-SN outburst in SN 2021bnw
  8. Conclusions

Figures (2)

  • Figure 1: Pseudo-bolometric LCs of the STELLA models m6W1 (purple), m7W1 (green), m8W2 (grey), m2W1 (light blue), and m1W5 (red), and he90W2 (dark blue), together with SN 2021bnw (circles). The numbers in legend are: ejecta mass, CSM mass, and CSM radius. Full list of physical parameters of the models can be found in Table \ref{['tab:stellapar']}.
  • Figure 2: Pseudo-bolometric LCs of SN 2021bnw (circles) zoomed in at the early epoch, including additional models. Among models are: m1W3 (light blue) with a compact CSM, and two shell-models m7T1 (blue) and m8T2 (red). Full list of model parameters is presented in Table \ref{['tab:stellapar']}. The grey curve corresponds to one of the models plotted in Figure \ref{['figure:main']} (m8W2, grey).