Highest Energy Astrophysical Photons Detected

Abstract

We report on the highest energy photons from the Crab Nebula observed by the Tibet air shower array with the underground water-Cherenkov-type muon detector array. Based on the criterion of a muon number measured in an air shower, we successfully suppress 99.92% of the cosmic-ray background events with energies E > 100 TeV. As a result, we observed 24 photonlike events with E > 100 TeV against 5.5 background events, which corresponds to a 5.6σ statistical significance. This is the first detection of photons with E > 100 TeV from an astrophysical source.