TeV gamma-ray observations of Southern BL Lacs with the CANGAROO 3.8m Imaging Telescope

(Astron. Astrophys., in press)

M.D. Roberts, S.A. Dazeley, P.G. Edwards, T. Hara, Y. Hayami, J. Holder, F. Kakimoto, S. Kamei, A. Kawachi, T. Kifune, R. Kita, T. Konishi, A. Masaike, Y. Matsubara, T. Matsuoka, Y. Mizumoto, M. Mori, H. Muraishi, Y. Muraki, K. Nishijima, S. Oda, S. Ogio, J.R. Patterson, G.P. Rowell, T. Sako, K. Sakurazawa, R. Susukita, A. Suzuki, R. Suzuki, T. Tamura, T. Tanimori, G.J. Thornton, S. Yanagita, T. Yoshida and T. Yoshikoshi

Observational and theoretical results indicate that low-redshift BL~Lacertae objects are the most likely extragalactic sources to be detectable at TeV energies. In this paper we present the results of observations of 4 BL~Lacertae objects (PKS0521$-$365, EXO\,0423.4$-$0840, PKS2005$-$489 and PKS2316$-$423) made between 1993 and 1996 with the CANGAROO 3.8\,m imaging \v Cerenkov telescope. During the period of these observations the gamma-ray energy threshold of the 3.8m\,telescope was $\sim$2\,TeV. Searches for steady long-term emission have been made, and, inspired by the TeV flares detected from Mkn~421 and Mkn~501, a search on a night-by-night timescale has also been performed for each source. Comprehensive Monte Carlo simulations are used to estimate upper limits for both steady and short timescale emission.