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A Markov Chain Monte Carlo technique to sample transport and source parameters of Galactic cosmic rays: II. Results for the diffusion model combining B/C and radioactive nuclei

Abstract : On-going measurements of the cosmic radiation (nuclear, electronic, and gamma-ray) are shedding new light on cosmic-ray physics. A comprehensive picture of these data relies on an accurate determination of the transport and source parameters of propagation models. A Markov Chain Monte Carlo is used to obtain these parameters in a diffusion model. From the measurement of the B/C ratio and radioactive cosmic-ray clocks, we calculate their probability density functions, with a special emphasis on the halo size L of the Galaxy and the local underdense bubble of size r_h. The analysis relies on the USINE code for propagation and on a Markov Chain Monte Carlo technique (Putze et al. 2009, paper I of this series) for the parameter determination. As found in previous studies, the B/C best-fit model favours diffusion/convection/reacceleration (Model III) over diffusion/reacceleration (Model II). A combined fit on B/C and the isotopic ratios (10Be/9Be, 26Al/27Al, 36Cl/Cl) leads to L ~ 8 kpc and r_h ~ 120 pc for the best-fit Model III. This value for r_h is consistent with direct measurements of the local interstallar medium. For Model II, L ~ 4 kpc and r_h is consistent with zero. We showed the potential and usefulness of the Markov Chain Monte Carlo technique in the analysis of cosmic-ray measurements in diffusion models. The size of the diffusive halo depends crucially on the value of the diffusion slope delta, and also on the presence/absence of the local underdensity damping effect on radioactive nuclei. More precise data from on-going experiments are expected to clarify this issue.
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Contributor : Emmanuelle Vernay <>
Submitted on : Tuesday, January 5, 2010 - 5:05:29 PM
Last modification on : Tuesday, December 8, 2020 - 3:39:45 AM

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A. Putze, L. Derome, D. Maurin. A Markov Chain Monte Carlo technique to sample transport and source parameters of Galactic cosmic rays: II. Results for the diffusion model combining B/C and radioactive nuclei. Astronomy and Astrophysics - A&A, EDP Sciences, 2010, 516, pp.A66. ⟨10.1051/0004-6361/201014010⟩. ⟨in2p3-00444114⟩

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