Extremely High Energy (E > 1020 eV) Cosmic Rays: Potential Sources

Abstract

One of the unsolved problems of cosmic ray physics is determining the nature and sources of ultrahigh energy cosmic rays (UHECRs, E > 1018 eV). The high degree of isotropy of the observed UHECR intensity caused mainly by the deviations of the UHECR trajectories in extragalactic and Galactic magnetic fields, as well as the significant uncertainty in their chemical composition (atomic mass), preclude one from tracing the observed events to their sources and finding the mechanisms for their acceleration. There are two ways to reduce the influence of magnetic deflection: by considering events with extremely high energy (EHECR, E > 1020 eV) and taking into account modern models of the Galactic magnetic field to correct its influence on the EHECR trajectory. In this study, the observed arrival directions of EHECRs from the Pierre Auger Observatory (PAO) and Telescope Array (TA) detectors' data are adjusted for the influence of Galactic and random extragalactic magnetic fields. New celestial positions of EHECRs are compared to the samples of potential sources used by the PAO—17 active galactic nuclei (AGNs) with powerful gamma radiation (from the 2FHL catalog) and 23 starburst galaxies (radio-flux-selected)—as well as with samples of 42 radio-galaxies from the parameterized catalog of radio-galaxies and magnetars. Taking into account the energy loss length of the nuclear component (H, He, C, Si, Fe) of EHECRs in the extragalactic environment and the expected typical distances to potential sources (~100 Mpc for H and Si-Fe and ~50 Mpc for He and C), the astrophysical objects that could be sources of relevant events were distinguished in the above samples. The potential acceleration mechanisms in the selected objects are analyzed, and the contribution of possible Galactic sources to the observed EHECR flux is evaluated.