COSMIC-RAY ELECTRONS AND THE DIFFUSE GAMMA-RAY SPECTRUM

The bulk of the diffuse galactic gamma-ray emission above a few tens o f GeV has been conventionally ascribed to the decay of neutral pions p roduced in cosmic-ray interactions with interstellar matter. Cosmic-ra y electrons may, however, make a significant contribution to the gamma -ray spectrum at high energies, and even dominate at TeV-PeV energies depending on their injection spectral index and acceleration cut-off e nergy. If the injection spectrum is flat, the highest energy electrons will also contribute a diffuse hard x-ray/soft gamma-ray flux via syn chrotron emission, and this may offer an explanation for the OSSE obse rvation of a steep spectrum below a few MeV from the inner Galaxy. We perform a propagation calculation for cosmic-ray electrons, and use th e resulting interstellar electron spectrum to obtain the gamma-ray spe ctrum due to inverse Compton, synchrotron and bremsstrahlung interacti ons consistently from MeV to PeV energies. We compare our results with available observations from satellite-borne telescopes, optical Ceren kov telescopes and air shower arrays and place constraints on the inje ction spectrum of cosmic-ray electrons. With future observations at Te V-PeV energies it should be possible to determine the average interste llar spectrum of cosmic-ray electrons, and hence estimate their spectr um on acceleration.