Propagation of UHE Protons through Magnetized Cosmic Web

TL;DR

This study models the propagation of ultra-high-energy protons through magnetized cosmic structures, showing potential correlations between arrival directions and source locations, and emphasizing the importance of nearby sources for the highest energy cosmic rays.

Contribution

It introduces a novel turbulence dynamo-based model of intergalactic magnetic fields and simulates UHECR trajectories considering realistic magnetic environments and energy losses.

Findings

70% of UHECRs above 60 EeV arrive within 15 degrees of their sources

Arrival time delays are typically less than 10^7 years

Nearby sources within 20 Mpc significantly contribute to >10^{20} eV flux

Abstract

If ultra-high-energy cosmic rays (UHECRs) originate from extragalactic sources, understanding the propagation of charged particles through the magnetized large scale structure (LSS) of the universe is crucial in the search for the astrophysical accelerators. Based on a novel model of the turbulence dynamo, we estimate the intergalactic magnetic fields (IGMFs) in cosmological simulations of the formation of the LSS. Under the premise that the sources of UHECRs are strongly associated with the LSS, we consider a model in which protons with E >10^{19} eV are injected by sources that represent active galactic nuclei located inside clusters of galaxies. With the model IGMFs, we then follow the trajectories of the protons, while taking into account the energy losses due to interactions with the cosmic background radiation. For observers located inside groups of galaxies like ours, about 70% and 35% of UHECR events above 60 EeV arrive within ~15 degree and ~5 degree, respectively, of the source position with time delays of less than ~10^7 yr. This implies that the arrival direction of super-GZK protons might exhibit a correlation with the distribution of cosmological sources on the sky. In this model, nearby sources (within 10 - 20 Mpc) should contribute significantly to the particle flux above ~10^{20} eV.