Impact of emission geometry and extragalactic magnetic fields on the energy spectrum of Ultra-High-Energy Cosmic Rays from astrophysical jets

Abstract

Ultra-high-energy cosmic rays (UHECRs) are particles with energies above 1018 eV that reach the Earth’s atmosphere from outer space. Their origin, acceleration mechanisms and emission processes remain unknown. Several models have been proposed in an attempt to answer these questions. Many of them attribute their extreme energies to powerful astrophysical jets. In this work, we considered a jetted astrophysical source as the origin of these particles. Understanding how the jet orientation relative to Earth affects observational signatures is crucial to interpret UHECR data. Using the CRPropa3 code, we performed numerical simulations of UHECR propagation in extragalactic magnetic fields, accounting for all relevant interaction processes with background photon fields within the energy range of these particles, as well as the effects of the universe’s adiabatic expansion. Our results demonstrate that, under certain conditions, emission geometry can play a decisive role in shaping the observed spectrum. These findings provide new insights into the conditions necessary for detecting UHECRs from jets and highlight the interplay between emission geometry and magnetic fields in determining the observed energy spectra.