Radio and X-Ray Emission as Probes of Type IIP Supernovae and Red Supergiant Mass Loss

Type IIP (plateau) supernovae are thought to come from stars with initial mass about 8-25 solar masses that end their lives as red supergiants. The expected stellar end points can be found from evolutionary calculations and the corresponding mass loss properties at this point can be estimated from typical values for Galactic stars. The mass loss densities of observed supernovae can be estimated from observations of the thermal X-ray and radio synchrotron emission that result from the interaction of the supernova with the surrounding wind. Type IIP supernovae are expected to have energy-conserving interaction during typical times of observation. Because Type IIP supernovae have an extended period of high optical luminosity, Compton cooling can affect the radio emitting electrons, giving rise to a relatively flat radio light curve in the optically thin regime. Alternatively, a high efficiency of magnetic field production results in synchrotron cooling of the radio emitting electrons. Both the X-ray and radio luminosities are sensitive to the mass loss and initial masses of the progenitor stars, although the turn-on of radio emission is probably the best estimator of circumstellar density. Both the mass loss density and the variation of density with stellar mass are consistent with expectations for the progenitor stars deduced from direct observations of recent supernovae. Current observations are consistent with mass being the only parameter; observations of a supernova in a metal poor region might show how the mass loss depends on metallicity.