RADIO-EMISSION FROM YOUNG SUPERNOVA-REMNANTS .2. EVOLUTION AND DEPENDENCE ON CHARACTERISTICS OF THE PROGENITOR AND THE EXTERNAL MEDIUM

During the evolution of a supernova remnant (SNR), some of the explosion energy is converted to relativistic electron energy at the shock front; and, to the extent that the circumstellar medium (CSM) is clumpy, turbulent dynamo processes associated with the growth of Rayleigh-Taylor (R-T) fingers convert explosion kinetic energy into magnetic field energy. Phenomenological descriptions of these processes have been incorporated into a one-dimensional, spherical hydrodynamics program. Input parameters used in the calculations included the explosion energy, the mean CSM density, and various characteristics of the clump CSM. In this paper the evolution of global properties such as total magnetic energy and luminosity are related to the input parameters through the use of power-law fits and heuristic scaling functions. The results show that, once an SNR reaches the Sedov phase of evolution, it evolves along a track parallel to the observed surface brightness (SIGMA)-diameter (D) relation for Galactic and Magellanic Cloud SNRs. We conclude that the observed range in surface brightness for a given diameter (a factor of about 30) is probably the result of variations in explosion energy (up to a factor of 8) and/or in the contrast between the mean CSM density and the peak density of individual clumps (up to a factor of 20).