Ponente
Descripción
Ultra-high-energy cosmic rays (UHECRs) get deflected by extragalactic magnetic fields (EGMFs) when they propagate from their sources to Earth. The spread of UHECRs around their source position provides a measure of the strength of the turbulent EGMFs between the UHECR sources and Earth. Recent results from the Pierre Auger Observatory suggest correlations between the arrival directions of UHECRs with $E > 32$ EeV and catalogues of starburst galaxies (SGBs) and jetted active galactic nuclei (AGNs) [1]. We re-interpret these observations using the same methodology but taking EGMF deflections into account [2]. Including EGMF deflections allows us to obtain upper limits on the strength of turbulent EGMFs between nearby UHECR sources and the Milky Way (not necessarily EGMFs in voids) under the conservative assumption of negligible deflections in the Galactic magnetic field. When including EGMF deflections for the corresponding source distances, the expected anisotropies in arrival directions of jetted AGN are dominated by Centaurus A only, contrary to Auger's analysis, where Mrk 421 and NGC 1275 contribute significantly as well. For SBGs, the same sources as in Auger's analysis dominate the correlations. Using our framework, we derive 90% CL upper limits for the turbulent EGMF strength (including its coherence length) between the dominant UHECR sources and the Milky Way of about 4 nG Mpc$^{1/2}$ for SBGs and 7 nG Mpc$^{1/2}$ for AGNs. These limits are significantly stronger than were found in a previous work using similar assumptions but different methods [3].
[1] Pierre Auger Collaboration, 2022, ApJ, 935, 170.
[2] AL-Zetoun A., Van Vliet A., Taylor A. M. and Winter W., 2025, arXiv:2506.16169.
[3] Van Vliet A., Palladino A., Taylor A. M. and Winter W., 2021, MNRAS, 510, 1289.
