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The Universe Viewed in Gamma-Rays 1 Observation of gamma-rays greater than 10 TeV from

By Kimihiro Okumura

Abstract

for CANGAROO collaboration We have observed Markarian 421 during an extraordinarily high state in January and March 2001 with the CANGAROO-II imaging Cherenkov telescope. From 14 hours observations at a large zenith angle of ∼70 ◦ , a signal of 298 ± 52 gamma-ray–like events was detected at E>10 TeV with 5.7 σ significance. Under the assumption of power-law spectrum, we derived a steep energy spectrum of photon index ∼4.0, and supports the evidence for a cutoff in the spectrum of Markarian 421. However, the 4 σ excess at energies greater than 20 TeV in our data favors a cutoff energy of ∼8 TeV, at the upper end of the range previously reported from measurements at TeV energies. 1

Year: 2012
OAI identifier: oai:CiteSeerX.psu:10.1.1.210.6099
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