Contribution to diffuse gamma-ray emission coming from self-confined CRs around their Galactic sources

TL;DR

This paper investigates how self-confined cosmic rays around their sources can produce extended gamma-ray halos, potentially explaining a significant part of the diffuse Galactic gamma-ray emission observed by Fermi-LAT.

Contribution

It introduces a model where self-confined cosmic rays create gamma-ray halos, offering a new explanation for the diffuse gamma-ray emission discrepancies.

Findings

Extended gamma-ray halos can account for a substantial fraction of observed diffuse emission.

The halos' contribution depends on the line of sight orientation and neutral density.

Self-confinement effects can significantly alter cosmic ray diffusion properties.

Abstract

Recent observations of the diffuse Galactic gamma-ray emission by the Fermi-LAT satellite have shown significant deviations from models which assume the same diffusion properties for cosmic rays (CR) throughout the Galaxy. We explore the possibility that a fraction of this diffuse Galactic emission could be due to hadronic interactions of CRs self-confined in the region around their sources. In fact, freshly accelerated CRs that diffuse away from the acceleration region can trigger the streaming instability able to amplify magnetic disturbance and to reduce the particle diffusion. When this happen, CRs are trapped in the near source region for a time longer than expected and an extended gamma-ray halo is produces around each source. Here we calculate the contribution to the diffuse gamma-ray background due to the overlap along lines of sight of several of these extended halos. We find that if the density of neutrals is low, the halos can account for a substantial fraction of the diffuse emission observed by Fermi-LAT, depending on the orientation of the line of sight with respect to the direction of the galactic center.