A Test for the Nature of the Type IA Supernova Explosion Mechanism

Abstract

Currently, popular models for Type Ia supernovae (SNe Ia) fall into two general classes. The first comprises explosions of nearly pure carbon/oxygen (C/O) white dwarfs (WDs) at the Chandrasekhar limit which ignite near their centers. The second consists of lower mass C/O cores which are ignited by the detonation of an accreted surface helium layer. Explosions of the latter type produce copious Fe, Co, and Ni Kα emission from 56Ni and 56Co decay in the detonated surface layers, emission which is much weaker from Chandrasekhar-mass models. The presence of this emission provides a simple and unambiguous discriminant between these two models for SNe Ia. Both mechanisms may produce 0.1-0.6 M_solar of 56Ni, making them bright γ-ray line emitters. The time to maximum brightness of 56Ni decay lines is distinctly shorter in the M<M_ch class of model (~15 days) than in the M_ch model (~30 days), making γ-ray line evolution another direct test of the explosion mechanism. It should just be possible to detect K-shell emission from a sub-M_ch explosion from SNe Ia as far away as the Virgo cluster with the XMM observatory. A 1-2 m² X-ray telescope such as the proposed Constellation-X observatory could observe Kα emission from M<M_ch SNe Ia in the Virgo cluster, providing not just a detection but high-accuracy flux and kinematic information.