A WC/WO star exploding within an expanding carbon-oxygen-neon nebula

TL;DR

This paper reports on the observation of a supernova within a carbon-oxygen-neon nebula, suggesting that some massive Wolf-Rayet stars can produce rapidly evolving transients, challenging previous assumptions about their end-of-life explosions.

Contribution

It provides evidence that massive WC/WO stars can explode within a nebula, contributing to the understanding of their role in rapidly evolving transients.

Findings

Supernova SN 2019hgp occurred within a carbon-oxygen-neon nebula.

The explosion's properties suggest a massive WC/WO star progenitor.

The event challenges the idea that such stars collapse directly into black holes without visible explosions.

Abstract

The final explosive fate of massive stars, and the nature of the compact remnants they leave behind (black holes and neutron stars), are major open questions in astrophysics. Many massive stars are stripped of their outer hydrogen envelopes as they evolve. Such Wolf-Rayet (W-R) stars emit strong and rapidly expanding (v_wind>1000 km/s) winds indicating a high escape velocity from the stellar surface. A fraction of this population is also helium depleted, with spectra dominated by highly-ionized emission lines of carbon and oxygen (Types WC/WO). Evidence indicates that the most commonly-observed supernova (SN) explosions that lack hydrogen and helium (Types Ib/Ic) cannot result from massive WC/WO stars, leading some to suggest that most such stars collapse directly into black holes without a visible supernova explosions. Here, we present observations of supernova SN 2019hgp, discovered about a day after explosion. The short rise time and rapid decline place it among an emerging population of rapidly-evolving transients (RETs). Spectroscopy reveals a rich set of emission lines indicating that the explosion occurred within a nebula composed of carbon, oxygen, and neon. Narrow absorption features show that this material is expanding at relatively high velocities (>1500 km/s) requiring a compact progenitor. Our observations are consistent with an explosion of a massive WC/WO star, and suggest that massive W-R stars may be the progenitors of some rapidly evolving transients.