Diffuse Galactic continuum gamma rays

Abstract

Galactic diffuse continuum gamma-ray emission is intricately related to cosmic-ray physics and radio astronomy. We describe recent results from an approach which endeavours to take advantage of this. Information from cosmic-ray composition constrains the propagation of cosmic rays; this in turn can be used as input for gamma-ray models. The GeV gamma-ray excess cannot be explained as neutral pion decay resulting from a hard nucleon spectrum without violating antiproton and positron data; the best explanation at present appears to be inverse-Compton emission from a hard interstellar electron spectrum. One consequence is an increased importance of Galactic inverse Compton for estimates of the extragalactic background. At low energies, an additional point-source component of gamma-rays seems to be necessary.