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

(Astron. Astrophys., in press)

M.D. Roberts, P.McGee, S.A. Dazeley, P.G. Edwards, T. Hara, Y. Hayami, J. Holder, A. Kawachi, T. Kifune, Y. Matsubara, Y. Mizumoto, M. Mori, H. Muraishi, Y. Muraki, T.Naito, K. Nishijima, S. Ogio, T. Osaki, J.R. Patterson, G.P. Rowell, T. Sako, K. Sakurazawa, R. Susukita, T. Tamura, T. Tanimori, G.J. Thornton, S. Yanagita, T. Yoshida and T. Yoshikoshi

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 3.8m telescope was around 1.5TeV. 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.