GAMMA-RAY PRODUCTION IN SUPERNOVA-REMNANTS

The bulk of cosmic rays of up to about 100 TeV are thought to be accel erated by the first-order Fermi mechanism at supernova shocks, produci ng a power-law spectrum. Both electrons and protons should be accelera ted, but their ratio on acceleration is not well known. Recently, the EGRET instrument on the Compton Gamma Ray Observatory has observed sup ernova remnants IC 443 and gamma Cygni at GeV energies. On the assumpt ion that the observed gamma-rays are produced by accelerated particles in the remnants (rather than, for example, from a central compact obj ect), we model the contributions from pion production, bremsstrahlung, and inverse Compton scattering on the cosmic microwave, diffuse galac tic, and locally produced radiation fields. In the case of the same sp ectral index for both electrons and nuclei and a cutoff at 80 TeV, we find that a spectral index of accelerated particles that is close to 2 .4 and a ratio of electrons to protons in the range 0.2-0.3 give a goo d fit to the observed spectra. For lower cutoff energies, flatter spec tra are possible. We also investigate the case in which the electron s pectrum is steeper than that of nuclei. We discuss the implications of our results for observations at air shower energies, and for the prop agation of cosmic rays.