The lowest metallicity type II supernova from the highest mass red-supergiant progenitor

TL;DR

This paper reports the discovery of a low-metallicity, high-mass red supergiant progenitor for a normal type II supernova, SN 2015bs, highlighting a potential link between progenitor mass, metallicity, and supernova characteristics.

Contribution

It provides the first evidence of a high-mass red supergiant progenitor at low metallicity for a typical type II supernova, expanding understanding of progenitor diversity.

Findings

Progenitor metallicity of SN 2015bs is ≤0.1Z$_\odot$.

Progenitor mass estimated at 17-25M$_\odot$.

SN 2015bs exhibits a normal plateau light curve.

Abstract

Red supergiants have been confirmed as the progenitor stars of the majority of hydrogen-rich type II supernovae. However, while such stars are observed with masses >25M$_\odot$, detections of >18M$_\odot$ progenitors remain elusive. Red supergiants are also expected to form at all metallicities, but discoveries of explosions from low-metallicity progenitors are scarce. Here, we report observations of the type II supernova, SN 2015bs, for which we infer a progenitor metallicity of $\leq$0.1Z$_\odot$ from comparison to photospheric-phase spectral models, and a Zero Age Main-Sequence mass of 17-25M$_\odot$ through comparison to nebular-phase spectral models. SN 2015bs displays a normal 'plateau' light-curve morphology, and typical spectral properties, implying a red supergiant progenitor. This is the first example of such a high mass progenitor for a 'normal' type II supernova, suggesting a link between high mass red supergiant explosions and low-metallicity progenitors.