NON-THERMAL PHOTON PRODUCTION VIA BULK COMPTONIZATION AT SUPERNOVA SHOCK BREAKOUT

We investigate the role of the bulk comptonization process in the propagation of thermal photons emitted at the shock breakout of a supernova explosion. We use a hydrodynamical model based on a self-similar solution for the shock breakout. The propagation of photons is treated by a Monte Carlo technique. Results of the simulations successfully reproduce the power-law spectrum observed by X-ray observations for XRF 080109/SN 2008D, if a mildly relativistic shock velocity is assumed. Effects of some radiative processes, photoionization, radiative recombination, and free-free absorption on the propagation of emitted photons are also investigated. It is found that any of them hardly changes the spectrum regarding the progenitor stars of Type Ib or Ic supernovae. Light curves calculated under the assumption of a spherical explosion indicate that the progenitor radius is required to be similar to 10(13) cm.