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

• Published in: Astroparticle physics 2009-02, Vol.31 (1), p.13-18
• Main Authors: Dimitrakoudis, Stavros, Mastichiadis, Apostolos, Geranios, Athanasios
• Format: Article
• Language: English
• ISSN: 0927-6505; 1873-2852
• DOI: 10.1016/j.astropartphys.2008.11.001

Recent observations by the H.E.S.S. collaboration of the Galactic Centre region have revealed what appears to be γ-ray emission from the decay of pions produced by interactions of recently accelerated cosmic rays with local molecular hydrogen clouds. Synthesizing a 3D hydrogen cloud map from the available data and assuming a diffusion coefficient of the form κ( E) = κ 0( E/ E 0) δ , we performed Monte Carlo simulations of cosmic ray diffusion for various propagation times and values of κ 0 and δ. By fitting the model γ-ray spectra to the observed one we were able to infer the value of the diffusion coefficient in that environment ( κ = 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 ⩽ γ ⩽ 2.3). Also, we found that proton losses can be substantial, which justifies our approach to the problem.