A Bayesian analysis of the 69 highest energy cosmic rays detected by the Pierre Auger Observatory

Abstract

The origins of ultrahigh energy cosmic rays (UHECRs) remain an open question. Several attempts have been made to cross-correlate the arrival directions of the UHECRs with catalogues of potential sources, but no definite conclusion has been reached. We report a Bayesian analysis of the 69 events, from the Pierre Auger Observatory (PAO), that aims to determine the fraction of the UHECRs that originate from known AGNs in the Veron-Cety & Verson (VCV) catalogue, as well as AGNs detected with the Swift Burst Alert Telescope (Swift-BAT), galaxies from the 2MASS Redshift Survey (2MRS), and an additional volume-limited sample of 17 nearby AGNs. The study makes use of a multilevel Bayesian model of UHECR injection, propagation and detection. We find that for reasonable ranges of prior parameters the Bayes factors disfavour a purely isotropic model. For fiducial values of the model parameters, we report 68 per cent credible intervals for the fraction of source originating UHECRs of 0.09-0.04+0.05, 0.25-0.08+0.09, 0.24-0.10+0.12, and 0.08-0.03+0.04 for the VCV, Swift-BAT and 2MRS catalogues, and the sample of 17 AGNs, respectively.