Deflagrations in hybrid CONe white dwarfs: a route to explain the faint Type Iax supernova 2008ha

TL;DR

This study models deflagrations in hybrid CONe white dwarfs near the Chandrasekhar mass, demonstrating they can produce faint Type Iax supernovae like SN 2008ha and potentially explain their diversity.

Contribution

It provides the first detailed hydrodynamic and nucleosynthesis simulations of deflagrations in hybrid CONe white dwarfs, linking them to faint Type Iax supernovae.

Findings

Ejected 0.014 Msun of material rich in iron-group elements, O, C, Si, and S.

Synthetic observables match the faint Type Iax SN 2008ha.

Hybrid WDs near MCh can account for a small but significant fraction of SN Ia rate.

Abstract

Stellar evolution models predict the existence of hybrid white dwarfs (WDs) with a carbon-oxygen core surrounded by an oxygen-neon mantle. Being born with masses ~1.1 Msun, hybrid WDs in a binary system may easily approach the Chandrasekhar mass (MCh) by accretion and give rise to a thermonuclear explosion. Here, we investigate an off-centre deflagration in a near-MCh hybrid WD under the assumption that nuclear burning only occurs in carbon-rich material. Performing hydrodynamics simulations of the explosion and detailed nucleosynthesis post-processing calculations, we find that only 0.014 Msun of material is ejected while the remainder of the mass stays bound. The ejecta consist predominantly of iron-group elements, O, C, Si and S. We also calculate synthetic observables for our model and find reasonable agreement with the faint Type Iax SN 2008ha. This shows for the first time that deflagrations in near-MCh WDs can in principle explain the observed diversity of Type Iax supernovae. Leaving behind a near-MCh bound remnant opens the possibility for recurrent explosions or a subsequent accretion-induced collapse in faint Type Iax SNe, if further accretion episodes occur. From binary population synthesis calculations, we find the rate of hybrid WDs approaching MCh to be on the order of 1 percent of the Galactic SN Ia rate.