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Astron. Astrophys. 343, 691-696 (1999)

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TeV gamma-ray observations of three X-ray selected BL Lacs

M.D. Roberts 1,2, P. McGee 2, S.A. Dazeley 2, P.G. Edwards 3, T. Hara 4, J. Holder 1, A. Kawachi 1, T. Kifune 1, Y. Matsubara 7, Y. Mizumoto 8, M. Mori 1, H. Muraishi 6, Y. Muraki 7, T. Naito 8, K. Nishijima 10, S. Ogio 5, T. Osaki 5, J.R. Patterson 2, G.P. Rowell 1,2, T. Sako 7, K. Sakurazawa 5, R. Susukita 11, T. Tamura 12, T. Tanimori 5, G.J. Thornton 2, S. Yanagita 6, T. Yoshida 6 and T. Yoshikoshi 1

1 Institute for Cosmic Ray Research, University of Tokyo, Tokyo 188, Japan
2 Department of Physics and Mathematical Physics, University of Adelaide, South Australia 5005, Australia
3 Institute of Space and Astronautical Science, Kanagawa 229, Japan
4 Faculty of Commercial Science, Yamanashi Gakuin University, Yamanashi 400, Japan
5 Department of Physics, Tokyo Institute of Technology, Tokyo 152, Japan
6 Faculty of Science, Ibaraki University, Ibaraki 310, Japan
7 Solar-Terrestrial Environment Laboratory, Nagoya University, Aichi 464, Japan
8 National Astronomical Observatory of Japan, Tokyo 181, Japan
9 Faculty of Education, Miyagi University of Education, Miyagi 980, Japan
10 Department of Physics, Tokai University, Kanagawa 259, Japan
11 Institute of Physical and Chemical Research, Saitama 351-01, Japan
12 Faculty of Engineering, Kanagawa University, Kanagawa 221, Japan

Received 8 September 1998 / Accepted 1 December 1998


Despite extensive surveys of extragalactic TeV gamma-ray candidates only 3 sources have so far been detected. All three are northern hemisphere objects and all three are low-redshift X-ray selected BL Lacs (XBLs). In this paper we present the results of observations of the three nearest southern hemisphere XBLs (PKS0548-322, PKS2005-489 and PKS2155-304) with the CANGAROO 3.8m imaging telescope. During the period of observation we estimate that the threshold of the 3.8 m telescope was [FORMULA]1.5 TeV. Searches for both steady and short timescale emission have been performed for each source. Additionally, we are able to monitor the X-ray state of each source on a daily basis and we have made contemporaneous measurements of optical activity for PKS0548-322 and PKS2155-304.

Key words: gamma rays: observations – galaxies: BL Lacertae objects: individual: PKS0548-322, PKS2005-489, PKS2155-304

Send offprint requests to: roberts@icrr.u-tokyo.ac.jp

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© European Southern Observatory (ESO) 1999

Online publication: March 1, 1999