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

TL;DR

This paper introduces a new model for Galactic gamma-ray emission at very high energies, considering discrete cosmic-ray sources and different diffusion scenarios, to explain observed gamma-ray features and source detectability.

Contribution

It presents a novel model incorporating discrete cosmic-ray injections and compares homogeneous and inhomogeneous diffusion, offering new insights into PeV cosmic-ray sources and gamma-ray flux clumpiness.

Findings

Inhomogeneous diffusion constrains the number of PeVatrons to be small.

The model explains the small number of detected hadronic PeVatrons.

A potential explanation for the mismatch between gas density and gamma-ray flux.

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.