Ultrahigh-Energy Cosmic Rays Accelerated in FR Radio Galaxy Jets

Abstract

Ultrahigh-Energy Cosmic Rays Accelerated in FR Radio Galaxy Jets

Relativistic jets of radio galaxies are widely regarded as potential sources of ultra-high-energycosmic rays (UHECRs). In this study, we investigate the acceleration of UHECRs within the jets ofFanaroff–Riley (FR) type I and II galaxies through numerical simulations. To accurately capture the nonlineardynamics of ultra-relativistic jets, we employ a newly developed high-order relativistic hydrodynamic (RHD)code. Subsequently, we follow the transport and acceleration of cosmic rays using a Monte Carlo approach.Our results reveal that the most prominent acceleration occurs around the interface between the jet spine andbackflow (cocoon) via the so-called relativistic shear acceleration. Additionally, though less significant,contributions arise from shocks and turbulence within the backflow region. Based on these simulations, wepresent model spectra of UHECRs accelerated in FR I and II jets, which can be used to interpret UHECRobservations at Earth, particularly those originating from nearby radio galaxies.