X-Ray Light Curve and Spectra of Shock Breakout in a Wind

We investigate the properties of X-ray emission from shock breakout of a supernova in a stellar wind. We consider a simple model describing aspherical explosions, in which the shock front with an ellipsoidal shape propagates into the dense circumstellar matter. For this model, both X-ray light curves and spectra are simultaneously calculated using a Monte Carlo method. We show that the shock breakout occurs simultaneously in all directions in a steady and spherically symmetric wind. As a result, even for the aspherical explosion, the rise and decay timescales of the light curve do not significantly depend on the viewing angles. This fact suggests that the light curve of the shock breakout may be used as a probe of the wind mass-loss rate. We compare our results with the observed spectrum and light curve of X-ray outburst 080109/SN 2008D. The observation can be reproduced by an explosion with a shock velocity of 60% of the speed of light and circumstellar matter with a mass-loss rate of yr^-1.