OBSERVATION OF THE CRAB NEBULA GAMMA-RAY EMISSION ABOVE 220 GeV BY THE CAT CHERENKOV IMAGING TELESCOPE

The CAT imaging telescope, recently built on the site of the former solar plant “Thémis” (French Pyrénées), observed γ-rays from the Crab nebula from October 1996 to March 1997. This steady source, often considered as the standard candle of very-high-energy γ-ray astronomy, is used as a test-beam to probe the performances of the new telescope, particularly its energy threshold (220GeV at 20 zenith angle) and the stability of its response. Due to the finegrain camera, an accurate analysis of the longitudinal profiles of shower images is performed, yielding the source position in two dimensions for each individual shower.