Limit on an Isotropic Diffuse Gamma-Ray Population with HAWC

Abstract

Data from 105 days from the High Altitude Water Cherenkov Observatory (HAWC) have been used to place a new limit on an isotropic diffuse gamma-ray population above 10 TeV. High- energy isotropic diffuse gamma-ray emission is produced by unresolved extragalactic objects such as active galactic nuclei, with potential contributions from interactions of high-energy cosmic rays with the inter-Galactic medium, or dark matter annihilation. Isotropic diffuse gamma-ray emission has been observed up to nearly 1 TeV. Above this energy, only upper limits have been reported. Observations or limits of the isotropic photon population above these energies are very sensitive to local astrophysical particle production. Of particular note, we expect a photon population to accompany the TeV-PeV astrophysical neutrino detection seen in the IceCube instrument. Observations or limits of a photon population above this energy can point to the origin of these neutrinos, indicating whether they are within the gamma-ray horizon or not. HAWC, with superior sensitivity to gamma rays between 100 GeV and 100 TeV, continuously observes the overhead sky and will measure or constrain isotropic emission above 1 TeV. We present a limit above 10 TeV based on the background rejection achieved in a 105-day observation of the Crab Nebula with HAWC. The limit will improve substantially with additional data and study.

Presented at the 34th International Cosmic Ray Conference (ICRC2015), The Hague, The Netherlands. See arXiv:1508.03327 for all HAWC contributions

References in corpus (7)

• Evidence for High-Energy Extraterrestrial Neutrinos at the IceCube Detector
• Observation of High-Energy Astrophysical Neutrinos in Three Years of IceCube Data
• Observations of the Crab Nebula with H.E.S.S
• The spectrum of isotropic diffuse gamma-ray emission between 100 MeV and 820 GeV
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• A Combined Astrophysical and Dark Matter Interpretation of the IceCube HESE and Throughgoing Muon Events
• TeV Solar Gamma Rays From Cosmic-Ray Interactions