Non-thermal photon production via bulk comptonization at supernova shock breakout

TL;DR

This paper explores how bulk comptonization influences thermal photon spectra during supernova shock breakout, successfully reproducing observed X-ray spectra and analyzing effects of various radiative processes.

Contribution

It introduces a Monte-Carlo simulation of photon propagation during supernova shock breakout incorporating bulk comptonization effects, a novel approach in this context.

Findings

Reproduces observed X-ray spectra with mildly relativistic shocks

Radiative processes like photoionization minimally affect the spectrum

Progenitor star radius estimated to be around 10^13 cm

Abstract

We investigate roles 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 none 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 $/sim 10^{13}$ cm.