GAMMA-RAYS AND COSMIC-RAYS IN SUPERNOVA-REMNANTS WITH RADIATIVE COOLING

The evolution of supernova remnants (SNR's) is followed numerically taking into account the non-linear effects of particle acceleration in shock waves. These high energy particles produce neutral pions by collisions with the thermal plasma and these pi-0's decay into the observable gamma-rays. The cosmic rays are treated as a fluid and the time variation of the adiabatic index during the remnant evolution gamma-c of the cosmic rays as well as of the mean diffusion coefficient kappaBAR are estimated dynamically by a simplified theory. The models for SNR's include the injection of suprathermal particles in shock waves, heating of the thermal plasma due to dissipation of Alfven waves in the precursor region of the forward shock and radiative cooling. The supernova explosion energy is set to E(SN) = 10(51) erg. We discuss several SNR models with different efficiencies for the conversion of E(SN) into cosmic rays depending on physical parameters. The gamma-ray fluxes from pi-0-decay yield 10(-10) ph cm-2 s-1 for a typical remnant with a small amount of cosmic ray energy at a time of 300 yr and increase almost like R(s)3 due to geometric effects (R(s) denotes the radius of the forward shock). Remnants with higher fractions of cosmic rays or remnants evolving into a medium of higher ambient density produce gamma-ray fluxes of up to about 10(-6) ph cm-2 s-1 (normalized to a SNR at a distance of 1 kpc). The radius of the forward shock varies between 1 pc and 70 pc for these gamma-ray fluxes. In the latter case the gamma-ray fluxes are almost constant between 10(4) and 10(6) yr. The effects of radiative cooling alter the overall energetics of a SNR but between 10% and 30% of the initial explosion energy E(SN) is converted into high energy particles. The production of cosmic rays leads to lower temperatures and consequently radiative cooling is already important at earlier times during the SNR evolution. Although radiative cooling is relevant for the thermal structure of the remnant the motion of the shock wave is also influenced by the cosmic ray pressure. Several small scale structures (secondary shocks) are created in the down-stream region and pushed by the pressure of the high energy particles, causing fluctuations of the gamma-ray flux.