EXPLOSIONS IN THE INTERSTELLAR-MEDIUM

Energy injection by supernovae is one of the primary determinants of t he physical state of the interstellar medium and it is therefore essen tial to understand the impact of a supernova explosion upon the inters tellar medium. Prior to the onset of radiative losses, the expansion o f a supernova remnant (SNR) follows a universal solution: by proper sc aling of the length and time scales, all nonradiative SNRs with a give n form for the density distribution in the supernova ejecta and for th e density distribution in the ambient medium can be described by the s ame numerical solution. Analytic approximations are given for the traj ectories of the blastwave shock in the ambient medium and for the reve rse shock propagating back into the supernova ejecta for the case in w hich both the ambient medium and the ejecta have uniform density. Thes e solutions should be valuable in describing historical remnants such as SN 1006, Tycho, Kepler, and Cas A, all of which are intermediate be tween the ejecta-dominated stage and the Sedov-Taylor stage of SNR evo lution.