Correlation between Ultra-high Energy Cosmic Rays and Active Galactic Nuclei from Fermi Large Area Telescope

TL;DR

This study investigates whether gamma-ray loud active galactic nuclei are the main sources of ultra-high energy cosmic rays by analyzing their spatial correlation, finding the hypothesis unlikely unless magnetic field effects are significant.

Contribution

It provides a correlation analysis between gamma-ray loud AGN and UHECR arrival directions using Fermi and Pierre Auger data, offering new insights into cosmic ray origins.

Findings

Correlation between AGN and UHECR is weak without magnetic smearing.

Gamma-ray loud AGN are unlikely the dominant UHECR sources.

Large magnetic deflections could reconcile the correlation with AGN origin.

Abstract

We study the possibility that the $\gamma$-ray loud active galactic nuclei (AGN) are the sources of ultra-high energy cosmic rays (UHECR), through the correlation analysis of their locations and the arrival directions of UHECR. We use the $\gamma$-ray loud AGN with $d\le 100 {\rm Mpc}$ from the second Fermi Large Area Telescope AGN catalog and the UHECR data with $E\ge 55 {\rm EeV}$ observed by Pierre Auger Observatory. The distribution of arrival directions expected from the $\gamma$-ray loud AGN is compared with that of the observed UHECR using the correlational angular distance distribution and the Kolmogorov-Smirnov test. We conclude that the hypothesis that the $\gamma$-ray loud AGN are the dominant sources of UHECR is disfavored unless there is a large smearing effect due to the intergalactic magnetic fields.