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Title: Searches for correlation between UHECR events and high-energy gamma-ray Fermi-LAT data

The astrophysical sources responsible for ultra high-energy cosmic rays (UHECRs) continue to be one of the most intriguing mysteries in astrophysics. Here, we present a comprehensive search for correlations between high-energy (≳ 1 GeV) gamma-ray events from the Fermi Large Area Telescope (LAT) and UHECRs (≳ 60 EeV) detected by the Telescope Array and the Pierre Auger Observatory. We perform two separate searches. First, we conduct a standard cross-correlation analysis between the arrival directions of 148 UHECRs and 360 gamma-ray sources in the Second Catalog of Hard Fermi-LAT sources (2FHL). Second, we search for a possible correlation between UHECR directions and unresolved Fermi-LAT gamma-ray emission. For the latter, we use three different methods: a stacking technique with both a model-dependent and model-independent background estimate, and a cross-correlation function analysis. We also test for statistically significant excesses in gamma rays from signal regions centered on Cen A and the Telescope Array hotspot. There was no significant correlation is found in any of the analyses performed, except a weak (≲ 2σ) hint of signal with the correlation function method on scales ~ 1°. Upper limits on the flux of possible power-law gamma-ray sources of UHECRs are derived.
Authors:
 [1] ;  [2] ;  [3] ;  [4]
  1. Inst. of Physics Buenos Aires (IFIBA CONICET-UBA) and International Center for Advanced Studies (ICAS)(Argentina)
  2. RWTH Aachen Univ. (Germany). Inst. for Theoretical Particle Physics and Cosmology (TTK)
  3. NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States). Astrophysics Division and NASA Postdoctoral Program Fellow
  4. Univ. of Nova Gorica (Slovenia). Lab. for Astroparticle Physics; National Inst. of Nuclear Physics (INFN), Trieste (Italy)
Publication Date:
Grant/Contract Number:
AC02-76SF00515
Type:
Accepted Manuscript
Journal Name:
Journal of Cosmology and Astroparticle Physics
Additional Journal Information:
Journal Volume: 2016; Journal Issue: 12; Journal ID: ISSN 1475-7516
Publisher:
Institute of Physics (IOP)
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE
Contributing Orgs:
Fermi LAT Collaboration
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; ultra high energy cosmic rays; gamma ray experiments; gamma ray theory
OSTI Identifier:
1355719