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

Stavros Dimitrakoudis(1), Apostolos Mastichiadis(1), Athanasios Geranios(2)

(1) University of Athens, Physics Department, Section of Astrophysics, Astronomy and Mechanics, Panepistimioupoli 15771, Greece
(2) University of Athens, Nuclear and Particle Physics Department, Panepistimioupoli 15771, Greece

Paper: Astropart. Phys., 2008, in press

EPrint Server: 0812.0575


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) = \kappa0(E/E0)^ delta , we performed Monte Carlo simulations of cosmic ray diffusion for various propagation times and values of \kappa0 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 kpc2Myr-1 for E = 1012.5eV and for total propagation time 104 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.

Preprints available from the authors at sdimis@phys.uoa.gr , or the raw TeX (no figures) if you click here.

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