[OI] 6300,6364 in the nebular spectrum of a subluminous Type Ia supernova

TL;DR

This paper reports the first observation of [OI] emission in a subluminous Type Ia supernova, challenging existing explosion models and suggesting violent mergers as a plausible explanation.

Contribution

It presents the first detection of [OI] emission in a subluminous Type Ia supernova, providing new insights into explosion mechanisms.

Findings

Detection of [OI] 6300,6364 emission in SN 2010lp

Complex, double-peaked emission profile indicating non-spherical oxygen distribution

Challenges to standard thermonuclear explosion models

Abstract

In this letter a late-phase spectrum of SN 2010lp, a subluminous Type Ia supernova (SN Ia), is presented and analysed. As in 1991bg-like SNe Ia at comparable epochs, the spectrum is characterised by relatively broad [FeII] and [CaII] emission lines. However, instead of narrow [FeIII] and [CoIII] lines that dominate the emission from the innermost regions of 1991bg-like SNe, SN 2010lp shows [OI] 6300,6364 emission, usually associated with core-collapse SNe and never observed in a subluminous thermonuclear explosion before. The [OI] feature has a complex profile with two strong, narrow emission peaks. This suggests oxygen to be distributed in a non-spherical region close to the centre of the ejecta, severely challenging most thermonuclear explosion models discussed in the literature. We conclude that given these constraints violent mergers are presently the most promising scenario to explain SN 2010lp.