The collision of a strong shock with a gas cloud - A model for Cassiopeia A

Abstract

The behavior of a fast shock wave traveling through a gas in which there are dense clouds is analyzed to test the model in which the stationary filaments associated with Cas A are dense gas clouds excited by the shock wave resulting from a supernova explosion. Hydrodynamics is used to describe the flow resulting from a shock impinging on a cloud, and the flow is found to consist of shocks transmitted into, traveling around, and reflected from the cloud. Flows past hot and cold clouds and their effects are described, and the analysis is applied to a model for the X-ray emission from Cas A in which hard X-rays originate in the intercloud gas and soft X-rays originate in many hot clouds. Faint emission patches to the north of Cas A are interpreted as preshocked clouds which will probably become quasi-stationary condensations after being hit by the shock.