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

Abstract

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 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. No significant correlation is found in any of the analyses performed, except a weak ($⪅2\sigma$) hint of signal with the correlation function method on scales $\sim 1^{\circ }$. Upper limits on the flux of possible power-law gamma-ray sources of UHECRs are derived.

24 pages, 12 figures, accepted in JCAP

References in corpus (13)

• The spectrum of isotropic diffuse gamma-ray emission between 100 MeV and 820 GeV
• Depth of Maximum of Air-Shower Profiles at the Pierre Auger Observatory: Measurements at Energies above 10^17.8 eV
• Indications of Intermediate-Scale Anisotropy of Cosmic Rays with Energy Greater Than 57 EeV in the Northern Sky Measured with the Surface Detector of the Telescope Array Experiment
• Fermi Gamma-ray Imaging of a Radio Galaxy
• The Origin of the Extragalactic Gamma-Ray Background and Implications for Dark-Matter Annihilation
• Study of Ultra-High Energy Cosmic Ray Composition Using Telescope Array's Middle Drum Detector and Surface Array in Hybrid Mode
• Gamma-Ray and Neutrino Backgrounds as Probes of the High-Energy Universe: Hints of Cascades, General Constraints, and Implications for TeV Searches
• Tomography of the Fermi-LAT gamma-ray diffuse extragalactic signal via cross-correlations with galaxy catalogs
• A model-independent analysis of the Fermi Large Area Telescope gamma-ray data from the Milky Way dwarf galaxies and halo to constrain dark matter scenarios
• CRPropa: A Numerical Tool for the Propagation of UHE Cosmic Rays, Gamma-rays and Neutrinos
• The high-energy $\gamma$-ray emission of AP Librae
• Gamma ray signatures of ultra high energy cosmic ray accelerators: electromagnetic cascade versus synchrotron radiation of secondary electrons
• Synchrotron pair halo and echo emission from blazars in the cosmic web: application to extreme TeV blazars

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