SN 2019hgp, new type of supernova? Wolf-Rayet progenitor?

[Astronuc]

TL;DR

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, e.g., an exploding massive WC/WO star.

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

https://arxiv.org/abs/2111.12435

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.

before the supernova occurred, the progenitor star was surrounded by a nebula rich in carbon, nitrogen, and neon, while lacking the lighter elements of hydrogen and helium. The expansion of the nebula must have been driven by strong stellar winds. This matches the structure of a Wolf-Rayet star extremely well. So it looks like SN 2019hgp is the first example of a Wolf-Rayet supernova. Since then, similar supernovae have also been detected.

Because this supernova was identified by spectra of the surrounding nebula, it isn’t clear whether the explosion was a simple supernova, or whether it was a more complex hybrid process where the upper layer of the star exploded while the core collapsed directly to a black hole. It will take more observations to determine the details. What’s clear is that at least some Wolf-Rayet stars do not go silently into the night.

https://www.wis-tns.org/object/2019hgp

https://www.universetoday.com/154116/a-new-kind-of-supernova-has-been-discovered/

https://ui.adsabs.harvard.edu/abs/2021TNSAN..76...1G/abstract

Motivated by recent discovery and classification reports of transients with spectra showing prominent narrow emission lines of carbon and/or oxygen, but lacking lines of hydrogen and helium, we propose to use a new spectroscopic SN type - SN Icn - to refer to such objects.

https://en.wikipedia.org/wiki/Wolf–Rayet_star
https://en.wikipedia.org/wiki/Wolf–Rayet_star#Evolution

1987 - https://www.annualreviews.org/doi/10.1146/annurev.aa.25.090187.000553
1991 - https://ui.adsabs.harvard.edu/abs/1991IAUS..143..485H/abstract

August 2000 - https://ui.adsabs.harvard.edu/abs/2000A&A...360..227N/abstract

January 2011 - https://ui.adsabs.harvard.edu/abs/2011BSRSL..80..266M/abstract
October 2013 - https://ui.adsabs.harvard.edu/abs/2013A&A...558A.131G/abstract