An Emerging Class of Bright, Fast-evolving Supernovae with Low-mass Ejecta

TL;DR

This paper identifies and analyzes a new class of bright, fast-evolving supernovae with low ejecta mass, including historical examples, suggesting they originate from old white dwarf progenitors and constitute at least 1-2% of all supernovae.

Contribution

It introduces a new class of supernovae characterized by rapid evolution and low ejecta mass, supported by historical data and spectral analysis, expanding understanding of supernova diversity.

Findings

Fast light curves with rise time <7 days

Low ejecta mass (<0.15 M_Sun) inferred from remnants

Old stellar environments support white dwarf progenitors

Abstract

A recent analysis of supernova (SN) 2002bj revealed that it was an apparently unique type Ib SN. It showed a high peak luminosity, with absolute magnitude M_R -18.5, but an extremely fast-evolving light curve. It had a rise time of <7 days followed by a decline of 0.25 mag per day in B-band, and showed evidence for very low mass of ejecta (<0.15 M_Sun). Here we discuss two additional historical events, SN 1885A and SN 1939B, showing similarly fast light curves and low ejected masses. We discuss the low mass of ejecta inferred from our analysis of the SN 1885A remnant in M31, and present for the first time the spectrum of SN 1939B. The old environments of both SN 1885A (in the bulge of M31) and SN 1939B (in an elliptical galaxy with no traces of star formation activity), strongly support old white dwarf progenitors for these SNe. We find no clear evidence for helium in the spectrum of SN 1939B, as might be expected from a helium-shell detonation on a white dwarf, suggested to be the origin of SN 2002bj. Finally, the discovery of all the observed fast-evolving SNe in nearby galaxies suggests that the rate of these peculiar SNe is at least 1-2 % of all SNe.