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

Abstract

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, EXO0423.4−0840, PKS2005−489 and PKS2316−423) made between 1993 and 1996 with the CANGAROO 3.8m imaging Cˇ erenkov telescope. During the period of these observations the gamma-ray energy threshold of the 3.8m telescope was ∼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.