OBSERVATION OF 7-TEV GAMMA-RAYS FROM THE CRAB USING THE LARGE ZENITH ANGLE AIR CERENKOV IMAGING TECHNIQUE

We have observed the Crab pulsar/nebula from 1992 December to 1993 January to search for very high energy gamma rays, using an imaging air Cerenkov telescope of 3.8 m diameter, located at Woomera, Australia. Since the observation was carried out in the southern hemisphere, the zenith angle of the object is large, which results in a maximum sensitivity of approximately 10(-13) cm-2 s-1 with approximately 7 TeV threshold energy for detected gamma rays. With high angular resolution, the Cerenkov imaging technique is found to be useful at zenith angles 53-degrees-56-degrees. We report here possible evidence of detection with 4 sigma significance of very high energy gamma-rays above approximately 7 TeV from the Crab pulsar/nebula. The integral flux is estimated to be (7.6 +/- 1.9) x 10(-13) cm-2 s-1. The result is consistent with the revised spectrum of the Crab recently reported by the Whipple group (Lewis et al. 1993).