Leptonic origin of diffuse galactic high-energy gamma rays - Indications for a varying cosmic ray proton-to-electron ratio

Abstract

The flux of high-energy (more than 300 MeV) gamma rays - caused by nonthermal bremsstrahlung and inverse Compton scattering - and the synchrotron flux at 408 MHz are calculated with the same power-law spectrum of relativistic electrons. Both are compared with the values observed at higher latitudes in the anticenter direction by employing the COS-B data and the 408-MHz survey of Haslam et al. (1982). It is shown that with column densities for the interstellar gas taken from the literature the cosmic-ray-electron component accounts for nearly the total gamma-flux, provided the magnetic field strength is of the order 3-4 microG with an equivalent half-thickness of about 1200 pc. These findings demand a decrease of the cosmic-ray proton-to-electron ratio at higher latitudes in the anticenter direction compared to the value observed in the solar vicinity.