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 a few GeV measured by the Fermi Large Area Telescope toward 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 the 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.

• Received 9 December 2014

DOI:https://doi.org/10.1103/PhysRevD.91.083012