Detection Of Vhe Gamma-Rays From Mrk 501 With The Cat Imaging Telescope

The CAT imaging telescope on the site on the former solar plant Th'emis has been observing fl-rays from Mrk501 above 220 GeV in March and April 1997. This source is shown to be highly variable and the light curve is presented. The detected fl-ray rate for the most intense flare is in excess of 10 per minute. INTRODUCTION The CAT imaging telescope was recently built on the site of the former solar plant "Th'emis" (French Pyr'en'ees). The detector has a trigger threshold for fl-rays of ¸220 GeV near the zenith, with excellent source-location and energy-resolution capabilities. The detector has been operational since October, 1996. The active galactic nucleus (AGN) Markarian 501 was the second extragalactic source detected in the VHE domain , by the Whipple group (Quinn et al., 1996) with a flux level of a tenth that of the Crab. In 1996 observations, some flaring activity was noted (Weekes, 1997). OBSERVATIONS The CAT imaging Cherenkov telescope has observed Mrk 501 in March and April o..