Observation of gamma rays greater than 10 TeV from Markarian 421

K. Okumura, A. Asahara, G. V. Bicknell, P. G. Edwards, R. Enomoto, S. Gunji, S. Hara, T. Hara, S. Hayashi, C. Itoh, S. Kabuki, F. Kajino, H. Katagiri, J. Kataoka, A. Kawachi, T. Kifune, H. Kubo, J. Kushida, S. Maeda, A. MaeshiroY. Matsubara, Y. Mizumoto, M. Mori, M. Moriya, H. Muraishi, Y. Muraki, T. Naito, T. Nakase, K. Nishijima, M. Ohishi, J. R. Patterson, K. Sakurazawa, R. Suzuki, D. L. Swaby, K. Takano, T. Takano, T. Tanimori, F. Tokanai, K. Tsuchiya, H. Tsunoo, K. Uruma, A. Watanabe, S. Yanagita, T. Yoshida, T. Yoshikoshi

研究成果: Article査読

24 被引用数 (Scopus)


We have observed Markarian 421 in 2001 January and March with the CANGAROO-II imaging Cerenkov telescope during an extraordinarily high state at TeV energies. From 14 hr of observations at very large zenith angles, ∼70°, a signal of 298 ± 52 gamma-ray-like events (5.7 σ) was detected at E > 10 TeV, where a higher sensitivity is achieved than those of usual observations near the zenith, owing to a greatly increased collecting area. Under the assumption of an intrinsic power-law spectrum, we derived a differential energy spectrum dN/dE = (3.3 ± 0.9stat ± 0.3syst) × 10-13(E/10 TeV) -(4.0-0.6+0.9, stat±0.3syst) photons cm-2 s -1 TeV-1, which is steeper than those previously measured around 1 TeV and supports the evidence for a cutoff in the spectrum of Mrk 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.

ジャーナルAstrophysical Journal
1 II
出版ステータスPublished - 2002 11 1

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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