A low energy core-collapse supernova without a hydrogen envelope

TL;DR

This paper reports the discovery of the faintest hydrogen-poor core-collapse supernova, SN2008ha, suggesting such events are more common than previously thought and may be linked to some long-duration gamma-ray bursts.

Contribution

It provides the first evidence of faint, hydrogen-deficient core-collapse supernovae, challenging previous classifications and linking them to gamma-ray bursts.

Findings

SN2008ha is the faintest hydrogen-poor supernova observed.

Some peculiar thermonuclear supernovae may actually be faint core-collapse events.

Faint, hydrogen-stripped supernovae could be connected to certain gamma-ray bursts.

Abstract

The final fate of massive stars depends on many factors, including mass, rotation rate, magnetic fields and metallicity. Theory suggests that some massive stars (initially greater than 25-30 solar masses) end up as Wolf-Rayet stars which are deficient in hydrogen because of mass loss through strong stellar winds. The most massive of these stars have cores which may form a black hole and theory predicts that the resulting explosion produces ejecta of low kinetic energy, a faint optical display and a small mass fraction of radioactive nickel(1,2,3). An alternative origin for low energy supernovae is the collapse of the oxygen-neon core of a relatively lowmass star (7-9 solar masses) through electron capture(4,5). However no weak, hydrogen deficient, core-collapse supernovae are known. Here we report that such faint, low energy core-collapse supernovae do exist, and show that SN2008ha is the faintest hydrogen poor supernova ever observed. We propose that other similar events have been observed but they have been misclassified as peculiar thermonuclear supernovae (sometimes labelled SN2002cx-like events(6)). This discovery could link these faint supernovae to some long duration gamma-ray bursts. Extremely faint, hydrogen-stripped core-collapse supernovae have been proposed to produce those long gamma-ray bursts whose afterglows do not show evidence of association with supernovae (7,8,9).