A luminous, blue progenitor system for a type-Iax supernova

TL;DR

This paper reports the detection of a luminous, blue progenitor system for a type-Iax supernova, supporting the model of a white dwarf accreting from a helium-star companion as the origin.

Contribution

First direct identification of a progenitor system for a type-Iax supernova, providing evidence for the white dwarf helium-star accretion model.

Findings

Progenitor system was luminous and blue in pre-explosion images.

Progenitor's properties suggest a white dwarf accreting from a helium-star.

Future observations can confirm the progenitor's nature or suggest a massive star origin.

Abstract

Type-Iax supernovae (SN Iax) are stellar explosions that are spectroscopically similar to some type-Ia supernovae (SN Ia) at maximum light, except with lower ejecta velocities. They are also distinguished by lower luminosities. At late times, their spectroscopic properties diverge from other SN, but their composition (dominated by iron-group and intermediate-mass elements) suggests a physical connection to normal SN Ia. These are not rare; SN Iax occur at a rate between 5 and 30% of the normal SN Ia rate. The leading models for SN Iax are thermonuclear explosions of accreting carbon-oxygen white dwarfs that do not completely unbind the star, implying they are "less successful" cousins of normal SN Ia, where complete disruption is observed. Here we report the detection of the luminous, blue progenitor system of the type-Iax SN 2012Z in deep pre-explosion imaging. Its luminosity, colors, environment, and similarity to the progenitor of the Galactic helium nova V445 Puppis, suggest that SN 2012Z was the explosion of a white dwarf accreting from a helium-star companion. Observations in the next few years, after SN 2012Z has faded, could test this hypothesis, or alternatively show that this supernova was actually the explosive death of a massive star.