High-Energy Gamma Rays Probing Cosmic-Ray Spectral Differences thoughout the Galaxy

Abstract

Detailed spectra of the Galactic γ-ray emission (50 MeV-6 GeV) are derived from a combination of all the observations obtained with the COS-B satellite. These spectra indicate that the cosmic-ray (CR) proton spectrum is on average flatter in the outer Galaxy than in the inner Galaxy and locally by approximately ∝ E^0.4, and maybe more, suggesting that the energy dependence of the mean CR path length is flatter in the outer Galaxy. CR measurements for the solar vicinity are thus not characteristic for the whole Galaxy, in particular for the outer Galaxy. Possible explanations in terms of variations in the relative importance of CR diffusion, convection, and Fermi reacceleration throughout the Galaxy are discussed briefly.