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

EZEQUIEL ALVAREZ; ALESSANDRO CUOCO; NESTOR MIRABAL; GABRIJELA ZAHARIJAS

JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS

IOP PUBLISHING LTD

Lugar: Londres; Año: 2016

1475-7516

The astrophysical sources responsible for ultra high-energy cosmic rays (UHECRs)continue to be one of the most intriguing mysteries in astrophysics. We present a com-prehensive search for correlations between high-energy ( >∼ 1 GeV) gamma-ray eventsfrom the Fermi Large Area Telescope (LAT) and UHECRs ( >∼ 60 EeV) detected by theTelescope Array and the Pierre Auger Observatory. We perform two separate searches.First, we conduct a standard cross-correlation analysis between the arrival directions of148 UHECRs and 360 gamma-ray sources in the Second Catalog of Hard Fermi-LATsources (2FHL). Second, we search for a possible correlation between UHECR directionsand unresolved Fermi-LAT gamma-ray emission. For the latter, we use three differentmethods: a stacking technique with both a model-dependent and model-independentbackground estimate, and a cross-correlation function analysis. No significant correla-tion is found in any of the analyses performed, except a weak ( <∼ 2σ) hint of signal withthe correlation function method on scales ∼ 1 ◦ . Upper