Bayesian analysis of cosmic ray propagation: evidence against homogeneous diffusion

Abstract

The American Astronomical Society, find out more The American Astronomical Society, find out more The Institute of Physics, find out more The Institute of Physics, find out more BAYESIAN ANALYSIS OF COSMIC RAY PROPAGATION: EVIDENCE AGAINST HOMOGENEOUS DIFFUSION G. Jóhannesson1, R. Ruiz de Austri2, A. C. Vincent3, I. V. Moskalenko4,5 , E. Orlando4,5, T. A. Porter4,5, A. W. Strong6, R. Trotta7,8 , F. Feroz9, P. Graff10,11Show full author list Published 2016 June 3 • © 2016. The American Astronomical Society. All rights reserved. The Astrophysical Journal, Volume 824, Number 1 Citation G. Jóhannesson et al 2016 ApJ 824 16 Download Article PDF Figures Tables References Download PDF 1482 Total downloads 70 70 total citations on Dimensions. Turn on MathJax Get permission to re-use this article Share this article Share this content via email Share on Facebook Share on Twitter Share on Google+ Share on Mendeley Article information Abstract We present the results of the most complete scan of the parameter space for cosmic ray (CR) injection and propagation. We perform a Bayesian search of the main GALPROP parameters, using the MultiNest nested sampling algorithm, augmented by the BAMBI neural network machine-learning package. This is the first study to separate out low-mass isotopes (p, $\bar{p}$, and He) from the usual light elements (Be, B, C, N, and O). We find that the propagation parameters that best-fit $p,\bar{p}$, and He data are significantly different from those that fit light elements, including the B/C and 10Be/9Be secondary-to-primary ratios normally used to calibrate propagation parameters. This suggests that each set of species is probing a very different interstellar medium, and that the standard approach of calibrating propagation parameters using B/C can lead to incorrect results. We present posterior distributions and best-fit parameters for propagation of both sets of nuclei, as well as for the injection abundances of elements from H to Si. The input GALDEF files with these new parameters will be included in an upcoming public GALPROP update.