Obtaining Cosmic-Ray Propagation Parameters from Diffuse Very High Energy Gamma-Ray Emission from the Galactic Center Ridge

• Published in: The Astrophysical journal 2007-02, Vol.656 (2), p.841-846
• Main Authors: Büsching, I, de Jager, O. C, Snyman, J
• Format: Article
• Language: English
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1086/510611

The recent discovery of diffuse, very high energy (VHE) g-radiation from the Galactic center ridge by the HESS telescope allows for the first time the direct determination of the parameters of Galactic cosmic-ray propagation models. Whereas this discovery showed that the diffuse g-radiation can be explained by the interaction of VHE cosmic-ray (CR) protons with the interstellar gas located in several giant molecular clouds, we show in this paper that the associated diffusion coefficient for the protons depends on the epoch of activity of the central source of protons: Assuming that the supernova remnant (SNR) Sgr A East was responsible for the particle acceleration, we infer a diffusion coefficient for the Galactic center region of =1-5 kpc super(2) Myr super(-1) for a mean proton energy of 63 TeV. More specifically, for impulsive injection in a 5-10 kyr SNR, we infer a value of =1-2 kpc super(2) Myr super(-1), whereas for source activity timescales equal to the age of the SNR, the diffusion coefficient would increase to g 5 kpc super(2) Myr super(-1). These values are smaller than those inferred from local CR abundances. Finally, the above-mentioned values of for impulsive injection are equally valid if the required transient source of protons was due to an earlier epoch of stellar infall into the black hole Sgr A*.