EXPLOSIONS IN THE INTERSTELLAR-MEDIUM

Energy injection by supernovae is one of the primary determinants of the physical state of the interstellar medium and it is therefore essential to understand the impact of a supernova explosion upon the interstellar medium. Prior to the onset of radiative losses, the expansion of a supernova remnant (SNR) follows a universal solution: by proper scaling of the length and time scales, all nonradiative SNRs with a given form for the density distribution in the supernova ejecta and for the density distribution in the ambient medium can be described by the same numerical solution. Analytic approximations are given for the trajectories of the blastwave shock in the ambient medium and for the reverse shock propagating back into the supernova ejecta for the case in which both the ambient medium and the ejecta have uniform density. These solutions should be valuable in describing historical remnants such as SN 1006, Tycho, Kepler, and Cas A, all of which are intermediate between the ejecta-dominated stage and the Sedov-Taylor stage of SNR evolution.