Gamma-ray sky points to radial gradients in cosmic-ray transport

TL;DR

This paper proposes a position-dependent cosmic-ray transport model that explains gamma-ray observations across the Galaxy, including the Galactic center, without conflicting with local cosmic-ray data.

Contribution

It introduces a novel phenomenological model with spatially varying diffusion and convection, improving the fit to gamma-ray data across the Galaxy.

Findings

Reproduces gamma-ray spectra at various Galactic latitudes

Supports position-dependent cosmic-ray transport mechanisms

Aligns with local cosmic-ray measurements

Abstract

The standard approach to cosmic-ray (CR) propagation in the Galaxy is based on the assumption that local transport properties can be extrapolated to the whole CR confining volume. Such models tend to underestimate the gamma-ray flux above few GeV measured by the Fermi Large Area Telescope towards the inner Galactic plane. We consider here for the first time a phenomenological scenario allowing for both the rigidity scaling of the diffusion coefficient and convective effects to be position-dependent. We show that within this approach we can reproduce the observed gamma-ray spectra at both low and mid Galactic latitudes - including the Galactic center - without spoiling any local CR observable.