Published online by Cambridge University Press: 04 August 2017
Young SNRs expand to much larger radii in a cloudy ISM than in a homogeneous medium, and they can have large variations in the pressure. The collision between supernova ejecta and an ambient cloud can result in an expanding high pressure region (a “secondary blast wave”). Observations of MSH 15–52 can be accounted for in this manner. X-ray emission from both young and older SNRs can provide an important probe for inferring the structure of the ISM.