Revisiting Propagation Delays of Ultra-High-Energy Cosmic Rays from Long-lived Sources

TL;DR

This paper examines how propagation delays of ultra-high-energy cosmic rays affect their correlation with long-lived astrophysical sources and explores implications for magnetic field constraints and cosmic ray composition.

Contribution

It provides a detailed analysis of UHECR propagation delays in various magnetic field configurations, highlighting their impact on source correlation and magnetic field constraints.

Findings

UHECR delays can surpass AGN duty cycles, disrupting source correlation.

Propagation effects influence interpretations of UHECR anisotropies.

Constraints on UHECR composition can inform extragalactic magnetic field models.

Abstract

We revisit the time delay incurred during ultra-high energy cosmic ray (UHECR) propagation over cosmological distances and its potential impact on the correlation between UHECR directions of arrival and long-lived sources (i.e., with duty cycles of order of Myr, such as Active Galactic Nuclei (AGNs) and starburst galaxies), the UHECR chemical composition, and extragalactic magnetic field constraints. We propagate particles in different magnetic field configurations, spanning over an extended range of particle Larmor radii and magnetic field coherence lengths, also including attenuation losses. We conclude that UHECR delays could easily be comparable to (and longer than) AGN duty cycles, effectively erasing the correlation between known AGNs and UHECR anisotropies. We finally consider how strong constraints on the chemical composition of the heaviest UHECRs could enable a better characterization of extragalactic magnetic fields.