Reconciling 56Ni production in type Ia supernovae with double degenerate scenarios

Abstract

We combine the observed distribution of Type Ia supernova (SN Ia) 56Ni yields with the results of sub-Chandrasekhar detonation and direct collision calculations to estimate what mass white dwarfs (WDs) should be exploding for each scenario. For collisions, the average exploding WD mass must be peaked at ≈0.75 M⊙, significantly higher than the average field WD mass of ≈0.55-0.60 M⊙. Thus, if collisions produce most SNe Ia, then a mechanism must exist that favours higher mass WDs. On the other hand, in old stellar populations, collisions would naturally result in low-luminosity SNe Ia, and we suggest these may be related to 1991bg-like events. For sub-Chandrasekhar detonations, the average exploding WD mass must be peaked at ≈1.1 M⊙. This is similar to the average total mass in WD-WD binaries, but it is not clear whether double degenerate mergers would synthesize sufficient 56Ni to match observed yields. If not, then actual ≈1.1 M⊙ WDs would be needed for sub-Chandrasekhar detonations. Since such high-mass WDs are produced relatively quickly in comparison to the age of SN Ia environments, this would require either accretion on to lower mass WDs prior to ignition or a long time-scale between formation of the ≈1.1 M⊙ WD and ignition. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.