Cosmic-Ray Nuclei, Antiprotons and Gamma-rays in the Galaxy: a New Diffusion Model

TL;DR

This paper introduces a new numerical model for cosmic ray transport in the Galaxy that accounts for spatially varying diffusion coefficients, successfully matching observed secondary/primary ratios and gamma-ray profiles without requiring convection or re-acceleration.

Contribution

It presents a novel numerical code that models cosmic ray diffusion with a spatially dependent diffusion coefficient, improving the understanding of cosmic ray propagation and gamma-ray emission.

Findings

Uniform diffusion models match observed secondary/primary ratios and antiproton spectra.

Radial dependence of diffusion affects gamma-ray emission profiles.

Convection and re-acceleration are not necessary in the considered energy range.

Abstract

We model the transport of cosmic ray nuclei in the Galaxy by means of a new numerical code. Differently from previous numerical models we account for a generic spatial distribution of the diffusion coefficient. We found that in the case of radially uniform diffusion, the main secondary/primary ratios (B/C, N/O and sub-Fe/Fe) and the modulated antiproton spectrum match consistently the available observations. Convection and re-acceleration do not seem to be required in the energy range we consider: $1 < E < 10^3$ 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 the prediction of secondary/primary ratios, the simulated longitude profile of the diffuse $\gamma$-ray emission is significantly different from the uniform case and may agree with EGRET measurements without invoking ad hoc assumptions on the galactic gas density distribution.