BREMSSTRAHLUNG AND ENERGETIC ELECTRONS IN SUPERNOVAE

We first present explicit Monte Carlo calculations of the rate of Compton scattering and of the spectrum of recoil electrons per gram at discrete depths within models of supernovae. The abundant fast recoil electrons produce many interesting secondary physical processes, foremost of which are bremsstrahlung and X-ray lines created during collisions with ions as those electrons slow down. Our major objective is to calculate the bremsstrahlung emissivity within supernova interiors. Such bremsstrahlung power must exist in all supernovae that are bolometrically powered by radioactive decay; it requires no collisional shocks between fluid elements for its creation. The total power in bremstrahlung production is typically 1 x 10(-3) of the total radioactive power emitted as Co-56 and Co-57 gamma rays that initiate these processes. We calculate the spectrum of the bremsstrahlung emissivity and show it to be E-1.3 for a wide range of supernova models. We also calculate the radial and temporal dependence of that emissivity for two models of SN 1987A and for one model of a Type Ia and of a He core explosion model of a Type Ib. The spectrum emerging from the surface (the luminosity), which we then evaluate by Monte Carlo techniques, is sensitive to the photoelectric opacity and is inverted by it-roughly F(nu) is-proportional-to nu-1.0-1.5; i.e., the spectral luminosity of the bremsstrahlung component increases slowly between 1 and 30 keV even though the emissivity declines with energy within that energy band. We find the bremsstrahlung luminosity to dominate that of the primary scattered gammas for E < 20 keV. Both X-ray observations of supernovae and of circumstellar matter must take the bremsstrahlung luminosity into account.