A correlation between the highest energy cosmic rays and nearby active galactic nuclei detected by Fermi

TL;DR

This study finds significant correlations between ultra-high-energy cosmic rays and nearby gamma-ray loud active galactic nuclei, supporting the hypothesis that these extragalactic objects are sources of such cosmic rays, with magnetic deflections considered.

Contribution

It provides the first strong statistical evidence linking nearby gamma-ray loud AGNs to the origins of UHECRs, especially within 200 Mpc.

Findings

Strong correlation (5.4 sigma) between UHECRs and nearby AGNs within 200 Mpc.

Identification of 7 candidate AGNs likely producing UHECRs.

Large angular scale correlations suggest magnetic deflections of cosmic rays.

Abstract

We analyze the correlation of the positions of gamma-ray sources in the Fermi Large Area Telescope First Source Catalog (1FGL) and the First LAT Active Galactic Nuclei (AGN) Catalog (1LAC) with the arrival directions of ultra-high-energy cosmic rays (UHECRs) observed with the Pierre Auger Observatory, in order to investigate the origin of UHECRs. We find that Galactic sources and blazars identified in the 1FGL are not significantly correlated with UHECRs, while the 1LAC sources display a mild correlation (2.6 sigma level) on a ~2.4 degree angular scale. When selecting only the 1LAC AGNs closer than 200 Mpc, we find a strong association (5.4 sigma) between their positions and the directions of UHECRs on a ~17 degree angular scale; the probability of the observed configuration being due to an isotropic flux of cosmic rays is 5x10^{-8}. There is also a 5 sigma correlation with nearby 1LAC sources on a 6.5 degree scale. We identify 7 "gamma-ray loud" AGNs which are associated with UHECRs within ~17 degree and are likely candidates for the production sites of UHECRs: Centaurus A, NGC 4945, ESO 323-G77, 4C+04.77, NGC 1218, RX J0008.0+1450 and NGC 253. We interpret these results as providing additional support to the hypothesis of the origin of UHECRs in nearby extragalactic objects. As the angular scales of the correlations are large, we discuss the possibility that intervening magnetic fields might be considerably deflecting the trajectories of the particles on their way to Earth.