We compare the radio and soft X-ray brightness as a function of position within the young supernova remnant Cassiopeia A .
A moderately strong correlation ( r = 0.7 ) was found between the X-ray emission ( corrected for interstellar absorption ) and radio emission , showing that the thermal and relativistic plasmas occupy the same volumes and are regulated by common underlying parameters .
The logarithmic slope of the relationship , \ln ( S _ { X - ray } ) = 1.2 \times \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 , but their more detailed relationship is poorly constrained and probably shows significant scatter .

The strongest radio and X-ray absorption is found at the western boundary of Cas A .
Based on the properties of Cas A and the absorbing molecular cloud , we argue that they are physically interacting .

We also compare ASCA derived column densities with \lambda 21 cm H i and \lambda 18 cm OH optical depths in the direction of Cas A , in order to provide an independent estimate of ISM properties .
We derive an average value for the H i spin temperature of \approx 40 \arcdeg K and measure the ratio OH/H _ { 2 } , which is nominally larger than previous estimates .