Obtaining cosmic ray propagation parameters from diffuse VHE gamma ray emission from the Galactic center ridge

Abstract

The recent discovery of diffuse, VHE gamma radiation from the Galactic center ridge by the H.E.S.S. telescope allow for the first time the direct determination of parameters of galactic cosmic ray propagation models. In this paper we show that the diffuse gamma radiation near the Galactic center may be explained by the interaction of VHE cosmic ray (CR) protons with the interstellar gas located in several giant molecular clouds leading to a measurement of the cosmic ray diffusion coefficient for the galactic center region of k = 1.3 kpc^2 Myr^-1 for a mean proton energy of about 3 TeV, if we assume that the CR protons originated from a supernova event (Sgr A East), which took off about 10 kyr ago. This value of k is about 5 to 10 times smaller than the locally measured value.