S ep 2 00 9 X - and Gamma - Ray Flashes from Type Ia Supernovae ?

We investigate two potential mechanisms that will produce X-ray and γ-ray flashes from Type Ia supernovae (SN-Ia). The first mechanism is the breakout of the thermonuclear burning front as it reaches the surface of the white dwarf. The second mechanism is the interaction of the rapidly expanding envelope with material within an accretion disk in the progenitor system. Our study is based on the delayed detonation scenario because this can account for the majority of light curves, spectra, and statistical properites of ’Branch-normal’ SN-Ia. Based on detailed radiation-hydro calculation which include nuclear networks, we find that both mechanisms produce brief flashes of high energy radiation with peak luminosities of 10 − 10 erg/sec. The breakout from the white dwarf surface produces flashes with a rapid exponential decay by 3 to 4 orders of magnitude on time scales of a of a few tenths of a second and with most of the radiation in the X-ray and soft-γ-ray range. The shocks produced in gases in and around the binary will produce flashes with a characteristic duration of a few seconds with most of the radiation coming out as X and γ-rays. In both mechanisms, we expect a fast rise and slow decline and, after the peak, an evolution from hard to softer radiation due to adiabatic expansion. In many cases, flashes from both mechanisms will be superposed. The Xand γ-ray visibility of a SN-Ia will depend strongly on self absorption within the progenitor system, specifically on the properties of the accretion disk and its orientation towards the observer. Such X-ray and γ-ray flashes could be detected as triggered events by GammaRay Burst (GRB) detectors on satellites, with events in current GRB catalogs. We have searched through the GRB catalogs (for the BATSE, HETE, and Swift experiments) for GRBs that occur at the extrapolated time of explosion and in the correct direction for known Type Ia supernovae with radial velocity of less than 3,000 km s. For BATSE about 12.9 ± 3.6 nearby SNe Ia should have been detected, but only 0.8 ± 0.7 non-conincidental matches have been found. With the HETE and Swift satellites, we expect to see 5.6±1.3SN-Ia flashes from Dept. of Physics, Florida State University, 315 Keen Building, Tallahassee, Florida, 32306-4350 Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803