Seeing the Collision of a Supernova with its Companion Star

Dan Kasen (UC Santa Cruz)

Observations of supernovae have allowed us to characterize the outcome
of the explosion -- the burned and ejected stellar debris -- in
remarkable detail. But we still know very little about the starting
point. The progenitors of Type Ia supernovae, for example, are
thought to be white dwarfs in binary systems, but no direct
observational evidence exists to confirm the hypothesis, and we do not
know whether the secondary is a main sequence star, a red giant, or
another white dwarf. I suggest that we should actually be able to see
the supernova ejecta colliding with a companion star or disrupted
debris disk if we look carefully in the hours and days following the
explosion. I present both simple analytic arguments and multi-dimensional
numerical simulations which illuminate the radiation hydrodynamics of
these interactions and quantify the emission we can expect. The
results suggest that early time observations of supernovae at X-ray
through optical wavelengths offer a direct means of confirming the
binary nature of the progenitor systems and determining the nature of
the companion star.