Diffuse TeV Emission at the Galactic Centre

TL;DR

This paper investigates the origin of diffuse TeV gamma-ray emission at the Galactic Centre, concluding that relativistic protons accelerated in the inter-cloud medium best explain the observed emission profile.

Contribution

It proposes that diffuse TeV emission is primarily due to relativistic protons accelerated throughout the inter-cloud medium, ruling out Sagittarius A* and dispersed pulsar wind nebulae as sole sources.

Findings

Relativistic protons in the inter-cloud medium explain the TeV emission profile.

Sagittarius A* cannot account for the diffuse emission.

Dispersed pulsar wind nebulae do not match the observed emission profile.

Abstract

The High-Energy Stereoscopic System (HESS) has detected intense diffuse TeV emission correlated with the distribution of molecular gas along the galactic ridge at the centre of our Galaxy. Earlier HESS observations of this region had already revealed the presence of several point sources at these energies, one of them (HESS J1745-290) coincident with the supermassive black hole Sagittarius A*. It is still not entirely clear what the origin of the TeV emission is, nor even whether it is due to hadronic or leptonic interactions. It is reasonable to suppose, however, that at least for the diffuse emission, the tight correlation of the intensity distribution with the molecular gas indicates a pionic-decay process involving relativistic protons. In this paper, we explore the possible source(s) of energetic hadrons at the galactic centre, and their propagation through a turbulent medium. We conclude that though Sagittarius A* itself may be the source of cosmic rays producing the emission in HESS J1745-290, it cannot be responsible for the diffuse emission farther out. A distribution of point sources, such as pulsar wind nebulae dispersed along the galactic plane, similarly do not produce a TeV emission profile consistent with the HESS map. We conclude that only a relativistic proton distribution accelerated throughout the inter-cloud medium can account for the TeV emission profile measured with HESS.