Gilad Svirski, Ehud Nakar, Re'em Sari
Recent supernovae (SNe) detections have motivated renewed interest in SN
shock breakouts from stars surrounded by thick winds, including predictions of
observable hard X-rays. Wind breakouts on timescales of a day or longer are
currently the most probable for detection. Here we study the signal that
follows such events, assuming a wind density profile $\propto r^{-2}$, starting
from the breakout of the radiation mediated shock and tracing the evolution of
the collisionless shock which forms afterwards. The emission contains two
spectral components - soft (optical/UV) and hard (X-rays and possibly soft
gamma-rays). We find that during the breakout, the soft component temperature
can vary significantly from one event to another (10^4-10^6 K), where events
with longer breakout time, t_bo, are generally softer. The hard component is
always a minute fraction, ~10^-4, of the breakout emission, and its fraction of
the total luminosity rises quickly afterwards, gaining dominance at ~10-50
t_bo. The spectral evolution of the soft and hard components, as well as the
prospects for detection of X-rays, depend mostly on the breakout time. In early
breakouts (t_bo <~ 20 d for typical parameters) both components become harder
after the breakout, and the hard component becomes dominant while the
luminosity is still comparable to the breakout luminosity. In late breakouts
(t_bo >~ 80 d for typical parameters) the soft component becomes softer with
time and the hard component becomes dominant only after the luminosity has
dropped significantly. In terms of prospects for X-ray and soft gamma-ray
detections, it is best to observe 100-500 days after explosions with breakout
timescales between a week and a month.
View original:
http://arxiv.org/abs/1202.3437
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