The application of two-dimensional imaging to very high energy gamma ray astronomy

A technique has been developed to distinguish air showers generated by gamma rays from those generated by hadronic cosmic rays. The method involves the registration of the Cherenkov light images by a large aperture multi-phototube telescope at the Whipple Observatory in southern Arizona. The energy threshold is 0.4 TeV. The efficacy of the technique has been demonstrated by the detection of a signal from the Crab Nebula, a supernova remnant. The physics of shower development at TeV energies is demonstrated to be what is expected, and no support is found for the detection of anomalous signals from binary sources. The sensitivity of the technique is such that a five sigma gamma-ray signal from the Crab can be detected in just an hour of observation. Further improvements in the technique are under way; in particular, a second large aperture camera is now operated in conjunction with the original camera to give stereoscopic images of showers. When completed, this system will give a flux sensitivity a factor of ten below that now available