Obtaining the diffusion coefficient for cosmic ray propagation in the Galactic Centre Ridge through time-dependent simulations of their gamma-ray emission

TL;DR

This study uses time-dependent simulations to determine the cosmic ray diffusion coefficient in the Galactic Centre Ridge by fitting gamma-ray emission data, revealing key propagation parameters and source spectra.

Contribution

It introduces a method to infer the cosmic ray diffusion coefficient in the Galactic Centre using 3-D hydrogen maps and gamma-ray data fitting, accounting for proton losses.

Findings

Diffusion coefficient in the Galactic Centre: 3.0 +/- 0.2 kpc^2 Myr^-1 at 10^12.5 eV

Proton losses are significant in this environment

Source spectral index between 2.1 and 2.3

Abstract

Recent observations by the H.E.S.S. collaboration of the Galactic Centre region have revealed what appears to be gamma-ray emission from the decay of pions produced by interactions of recently accelerated cosmic rays with local molecular hydrogen clouds. Synthesizing a 3-D hydrogen cloud map from the available data and assuming a diffusion coefficient of the form kappa(E) = kappa_0(E/E0)^delta, we performed Monte Carlo simulations of cosmic ray diffusion for various propagation times and values of kappa_0 and delta. By fitting the model gamma-ray spectra to the observed one we were able to infer the value of the diffusion coefficient in that environment (kappa = 3.0 +/- 0.2 kpc^2 Myr^-1 for E = 10^12.5 eV and for total propagation time 10^4 yr) as well as the source spectrum (2.1 < gamma < 2.3). Also, we found that proton losses can be substantial, which justifies our approach to the problem.