SHOCK BREAKOUT FROM TYPE Ia SUPERNOVA

Abstract

The mode of explosive burning in Type Ia SNe remains an outstanding problem.\nIt is generally thought to begin as a subsonic deflagration, but this may\ntransition into a supersonic detonation (the DDT). We argue that this\ntransition leads to a breakout shock, which would provide the first unambiguous\nevidence that DDTs occur. Its main features are a hard X-ray flash (~20 keV)\nlasting ~0.01 s with a total radiated energy of ~10^{40} ergs, followed by a\ncooling tail. This creates a distinct feature in the visual light curve, which\nis separate from the nickel decay. This cooling tail has a maximum absolute\nvisual magnitude of M_V = -9 to -10 at approximately 1 day, which depends most\nsensitively on the white dwarf radius at the time of the DDT. As the thermal\ndiffusion wave moves in, the composition of these surface layers may be\nimprinted as spectral features, which would help to discern between SN Ia\nprogenitor models. Since this feature should accompany every SNe Ia, future\ndeep surveys (e.g., m=24) will see it out to a distance of approximately 80\nMpc, giving a maximum rate of ~60/yr. Archival data sets can also be used to\nstudy the early rise dictated by the shock heating (at about 20 days before\nmaximum B-band light). A similar and slightly brighter event may also accompany\ncore bounce during the accretion induced collapse to a neutron star, but with a\nlower occurrence rate.\n