On the gamma-ray fluxes expected from Cassiopeia A

Abstract

Based on the results of our previous study of the broad band synchrotron emission of Cas A in the framework of a spatial inhomogeneous model, we calculate the fluxes of gamma-radiation that can be expected from this supernova remnant in different energy bands. We show that at energies below 10 GeV gamma-ray fluxes detectable by forthcoming space-borne detectors should be produced due to bremsstrahlung of radio emitting electrons. We predict that the power-law index of the photon flux in the GeV region should be hard, close to the index ~2.2 expected for the acceleration spectrum of the electrons. Photon fluxes accessible to future ground-based gamma-ray detectors could also be expected at very high energies. The fluxes to be expected due to bremsstrahlung and inverse Compton radiation of relativistic electrons at TeV energies should be very steep, and strongly dependent on the characteristic magnetic fields in Cas A. We could expect also significant fluxes of pi^0 -decay gamma-rays produced by relativistic protons. These fluxes may extend with a hard spectrum beyond TeV energies as far as the protons would be accelerated to energies beyond 100 TeV. The hardness of the gamma-ray spectrum at TeV energies could in principle allow one to distinguish between electronic and hadronic origins of those gamma-rays. We discuss also other implications, such as relativistic particle content, or physical parameters in the source, that could be derived from future gamma-ray flux measurements in different energy bands.