PKS 2155-304 - a source of VHE γ-rays

Abstract The close X-ray selected BL Lac PKS 2155-304 has been observed using the University of Durham Mark 6 very high energy (VHE) gamma ray telescope during 1996 September/October/November and 1997 October/November. VHE gamma rays with energy > 300 GeV were detected with a time-averaged integral flux of (4.2 ± 0.7stat ± 2.0sys) × 10−11 cm−2 s−1. There is evidence for VHE gamma ray emission during our observations in 1996 September and 1997 October/November. The strongest emission was detected in 1997 November, when the object was producing a large flux of high-energy X-rays and was detected in > 100 MeV gamma-rays.