A COMPARISON OF X-RAY AND RADIO-EMISSION FROM THE SUPERNOVA REMNANT CASSIOPEIA-A

We compare the radio and soft X-ray brightnesses as a function of posi tion within the young supernova remnant Cassiopeia A. A moderately str ong correlation (r = 0.7) was found between the X-ray emission (correc ted for interstellar absorption) and radio emission, showing that the thermal and relativistic plasmas occupy the same volumes and are regul ated by common underlying parameters. The logarithmic slope of the rel ationship, ln S-X = 1.2 ln S-radio + ln k, implies that the variations in brightness are primarily due to path length differences. The X-ray and radio emissivities are both high in the same general locations, b ut their more detailed relationship is poorly constrained and probably shows significant scatter. The strongest radio and X-ray absorption i s found at the western boundary of Cas A. Based on the properties of C as A and the absorbing molecular cloud, we argue that they are physica lly interacting. We also compare column densities derived from the Adv anced Satellite for Cosmology and Astrophysics with 21 cm H I and 18 c m OH optical depths in the direction of Cas A, in order to provide an independent estimate of interstellar medium properties. We derive an a verage value for the H I spin temperature of approximate to 40 K and m easure the ratio OH/H-2, which is nominally larger than previous estim ates.