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

<p>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 similar to 1.1 M-aS (TM), hybrid WDs in a binary system may easily approach the Chandrasekhar mass (M-Ch) by accretion and give rise to a thermonuclear explosion. Here, we investigate an off-centre deflagration in a near-M-Ch 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 M-aS (TM) 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-M-Ch WDs can in principle explain the observed diversity of Type Iax supernovae. Leaving behind a near-M-Ch 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 M-Ch to be of the order of 1 per cent of the Galactic SN Ia rate.</p>