The CAT imaging telescope for very high-energy gamma-ray astronomy

Abstract The CAT (Cherenkov Array at Themis) imaging telescope, equipped with a very-high-definition camera (546 fast phototubes with 0.12° spacing surrounded by 54 larger tubes in two guard rings) started operation in Autumn 1996 on the site of the former solar plant Themis (France). Using the atmospheric Cherenkov technique, it detects and identifies very high energy γ-rays in the range 250 GeV to a few tens of TeV. The instrument, which has detected three sources (Crab nebula, Markarian 421 and Markarian 501), is described in detail.