High energy gamma-ray emission from supernova remnants

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Abstract
Since Galactic cosmic rays are believed to be created in supernova remnants (SNRs), SNRs are expected to be a source of high energy gamma -rays through the decay of neutral pions produced by p-p collisions. The characteristics of cosmic rays such as the maximum accelerated energy, spectral index and total energy in SNRs can be probed by their gamma -ray emission. Since the resultant gamma -ray spectrum is flatter than that of the Galactic background reflecting the difference of cosmic ray spectra in SNRs and in the Galaxy, SNRs are likely to be observed by gamma -rays at higher energies. For various spectra of cosmic rays in SNRs, we have calculated the gamma -ray spectra resulting from p-p collisions for an energy range from 0.01 GeV to 107 GeV. We show that for a reasonable choice of numerical values SNRs are observable against the gamma -ray background and cosmic ray background with existing and future instruments such as EGRET on board the GRO satellite, Cerenkov telescopes and air shower arrays over various energy bands.