Bayesian inference on the galactic magnetic field toward the south galactic pole using UHECRs

Abstract

Owing to the Pierre Auger observatory (PAO), we have an unprecedented amount of ultra-high-energy cosmic ray (UHECR) data. Using the data, we study the influence of the galactic magnetic field (GMF) on the trajectory of UHECRs with energy above 6 x 10^19 eV. The GMF is not uniform and its configuration is still uncertain. Besides, most studies on the GMF have been about the disk field. In this study, we focus on the GMF toward the south galactic pole (SGP), which is thoroughly within the field of view of the PAO. We examine the effects of the GMF on the arrival direction of UHECRs by statistical tests of correlation to the large-scale structure of the universe. The deflection angle of UHECRs affected by the GMF is inferred through the Bayesian inference with Monte-Carlo simulations. We present the estimated strength of the GMF toward the SGP based on the deflection angle, and discuss the implications of our results.