Gamma Rays frim the Galactic Centre

TL;DR

This paper proposes that the diffuse gamma-ray emission from the Galactic Centre is due to cosmic ray protons diffusing from supernova remnants, with evidence supporting anomalous diffusion and low acceleration efficiency in high-density regions.

Contribution

It introduces a model explaining gamma-ray flux via proton diffusion from SNRs, emphasizing anomalous diffusion and low acceleration efficiency in dense regions.

Findings

Correlation between cosmic ray intensity and 5 GHz radio emission.

Necessity of anomalous diffusion for explaining gamma-ray distribution.

Low efficiency of SNR acceleration in high-density regions.

Abstract

Recent results from the HESS gamma ray telescope have shown the presence of both a diffuse, extended, flux of gamma rays above ~0.4 TeV and discrete sources in and near the Galactic Centre. Here, we put forward a possible explanation in terms of the diffusion of cosmic ray protons from a succession of supernova remnants (SNR) in the SgrA* region of the Galaxy plus a contribution from SNR in the rest of the Galactic Centre Region, to be called the Galactic Centre Ridge (GCR). Protons are favoured over electrons because the mG magnetic fields in the Region will attenuate energetic electrons severely. Prominent features are the need for 'anomalous diffusion' of the protons in the whole region and the adoption of low efficiency for SNR acceleration in the high density regions. The latter is related by us to the well-known low 'cosmic ray gradient' in the Galaxy. A corroborating feature is the close correlation of inferred cosmic ray intensity with the smoothed intensity of 5 GHZ radio radiation. We attribute this to the presence of the SNR in the GCR.