Cosmic ray nuclei, antiprotons and gamma rays in the galaxy: a new diffusionmodel

Abstract

We model the transport of cosmic ray nuclei in the galaxy by means of a new numericalcode. At variance with previous numerical models, ours accounts for a generic spatialdistribution of the diffusion coefficient. We found that in the case of radially uniformdiffusion, the main secondary/primary ratios (B/C, N/O and sub-Fe/Fe) and themodulated antiproton spectrum consistently match the available observations. Convectionand re-acceleration do not seem to be required in the energy range that we consider:1≤E≤103 GeV/nucleon. We generalize these results, accounting for radial dependence of the diffusion coefficient,which is assumed to trace that of the cosmic ray sources. While this does not affect theprediction of secondary/primary ratios, the simulated longitude profile of the diffuseγ-ray emission is significantly different from that for the uniform case and may agree withEGRET measurements without requiring invoking ad hoc assumptions on the galactic gasdensity distribution.