Non-thermal emission from supernova shock breakout and the origin of the   X-ray transient associated with SN2008D
  We suggest that non-thermal emission can be produced by multiple scatterings of the photons between the supernova ejecta and pre-shock material in supernova shock breakout. Such bulk-Comptonization process may significantly change the original thermal photon spectrum, forming a power-law non-thermal component at higher energies. We then show that the luminous X-ray outburst XRO081009 associated with SN2008D is likely to be such shock breakout emission from an ordinary type Ib/c supernova. 
Xiang-Yu Wang, Zhuo Li, Eli Waxman and Peter Meszaros