Imprints of PeV cosmic-ray sources on the diffuse gamma-ray emission

Abstract

We present our new model for the description of the very high energy Galactic gamma-ray emission based on a discrete injection of cosmic rays by individual sources. We investigate the morphology of the very high energy gamma-ray sky, the detectability of cosmic-ray sources and the clumpiness of the diffuse gamma-ray flux, assuming two different scenarios for cosmic-ray propagation. Namely, a standard isotropic and homogeneous diffusion process and an isotropic and inhomogeneous diffusion process. We notably formulate a possible explanation to the small number of hadronic PeVatrons recently detected by LHAASO. In the case of the inhomogeneous diffusion process, we constrain the number of hadronic PeVatrons to be small. Finally, we give an argument that may explain the discrepancy between the interstellar gas density distribution and the very high energy diffuse gamma-ray flux.