Constraining the Extragalactic Magnetic Field: Auger Data Meet UHECR Propagation Modeling

TL;DR

This paper refines constraints on the extragalactic magnetic field by analyzing Auger UHECR data with detailed propagation modeling, revealing limits on magnetic field strength and source contributions.

Contribution

It introduces a framework incorporating turbulent EGMFs into UHECR propagation analysis, improving source correlation understanding and magnetic field constraints.

Findings

Upper limits on EGMF strength: 4.4 nG Mpc^{1/2} for SBGs and 6.7 nG Mpc^{1/2} for AGNs.

Centaurus A dominates AGN correlations when accounting for deflections.

Galactic magnetic field upper limit: 1.4 μG kpc^{1/2} for a 30 kpc halo.

Abstract

Recent analyses from the Pierre Auger Collaboration suggest correlations between the arrival directions of Ultra-High-Energy Cosmic Rays (UHECRs) and catalogs of starburst galaxies (SGBs) and jetted active galactic nuclei (AGNs). We revisit these analyses using the same methodology as \auger , but explicitly incorporating UHECR deflections in turbulent extragalactic magnetic fields (EGMFs). We demonstrate that while for SBGs the same sources as for the generic \auger\ analysis dominate the catalog correlations, jetted AGNs are dominated by Centaurus~A when accounting for source distances and deflections. Using our framework, we derive 90\% confidence level upper limits on the local EGMF strength of 4.4~nG~Mpc$^{1/2}$ for SBGs and 6.7~nG~Mpc$^{1/2}$ for jetted AGNs. Assuming instead that the UHECR deflections predominantly arise from the Galactic magnetic field (GMF), we obtain a GMF upper limit of $1.4 \, \mu$G~kpc$^{1/2}$ for a Galactic halo size of 30~kpc.