Observation of an Extended Very High Energy Gamma-Ray Emission from MSH 15-52 with CANGAROO-III

T. Nakamori, H. Kubo, T. Yoshida, T. Tanimori, R. Enomoto, G. V. Bicknell, R. W. Clay, P. G. Edwards, S. Gunji, S. Hara, T. Hara, T. Hattori, S. Hayashi, Y. Higashi, Y. Hirai, K. Inoue, S. Kabuki, F. Kajino, H. Katagiri, A. Kawachi, T. Kifune, R. Kiuchi, J. Kushida, Y. Matsubara, T. Mizukami, Y. Mizumoto, R. Mizuniwa, M. Mori, H. Muraishi, Y. Muraki, T. Naito, S. Nakano, D. Nishida, K. Nishijima, M. Ohishi, Y. Sakamoto, A. Seki, V. Stamatescu, T. Suzuki, D. L. Swaby, G. Thornton, F. Tokanai, K. Tsuchiya, S. Watanabe, Y. Yamada, E. Yamazaki, S. Yanagita, T. Yoshikoshi, and Y. Yukawa

We have observed the supernova remnant MSH 15-52 (G320.4-1.2), which contains the gamma-ray pulsar PSR B1509-58, using the CANGAROO-III imaging atmospheric Cerenkov telescope array from 2006 April to June. We detected gamma rays above 810 GeV at the 7σ level during a total effective exposure of 48.4 hr. We obtained a differential gamma-ray flux at 2.35 TeV of (7.9+-1.5_stat+-1.7_sys)× 10^-13cm^-2s^-1TeV^-1, with a photon index of 2.21+-0.39_stat+-0.40_sys, which is compatible with that of the H.E.S.S. observation in 2004. The morphology shows extended emission compared to our point spread function. We consider the plausible origin of the high-energy emission based on a multiwavelength spectral analysis and energetics arguments.