  The X-ray flash 080109, associated with SN 2008D, can be attributed to the
shock breakout emission from a normal Type Ib/c supernova. If the observed
emission is interpreted as blackbody emission, the temperature and radiated
energy are close to expectations, considering that scattering dominates
absorption processes so that spectrum formation occurs deep within the
photosphere. The X-ray emission observed at ~10 days is attributed to inverse
Compton scattering of photospheric photons with relativistic electrons produced
in the interaction of the supernova with the progenitor wind. A simple model
for the optical/ultraviolet emission from shock breakout is developed and
applied to SN 1987A, SN 1999ex, SN 2008D, and SN 2006aj, all of which have
optical emission observed at t~1 day. The emission from the first three can
plausibly be attributed to shock breakout emission. The photospheric
temperature is most sensitive to the radius of the progenitor star core and the
radii in these cases are in line with expectations from stellar evolution. The
early optical/ultraviolet observations of SN 2006aj cannot be accommodated by a
shock breakout model in a straightforward way.

Astrophysics