Correlating Fermi gamma-ray sources with ultra-high energy cosmic rays

TL;DR

This study investigates the potential correlation between Fermi gamma-ray sources and ultra-high energy cosmic rays, finding no significant association despite some initial proximity, thus informing the ongoing debate about cosmic ray origins.

Contribution

The paper provides a systematic cross-correlation analysis between Fermi gamma-ray sources and UHECRs, demonstrating no significant correlation and highlighting the need for alternative origin hypotheses.

Findings

No significant correlation between Fermi sources and UHECRs.

Similar match rates in random gamma-ray burst samples.

Supports the hypothesis that UHECRs are not primarily from Fermi sources.

Abstract

The origin of ultra-high energy cosmic rays (UHECRs) is one of the enduring mysteries of high-energy astrophysics. To investigate this, we cross-correlate the recently released Fermi Large Area Telescope First Source Catalog (1FGL) with the public sample of UHECRs made available by the Pierre Auger collaboration. Of the 27 UHECRs in the sample, we find 12 events that arrived within 3.1 degrees of Fermi sources. However, we find similar or larger number of matches in 63 out of 100 artificial UHECR samples constructed using positions randomly drawn from the BATSE 4B catalog of gamma-ray bursts (GRBs) collected from 1991 until 1996. Based on our analysis, we find no evidence that UHECRs are associated with Fermi sources. We conclude with some remarks about the astrophysical origin of cosmic rays.