DETECTION OF ATMOSPHERIC CHERENKOV RADIATION USING SOLAR HELIOSTAT MIRRORS

There is considerable interest world-wide in developing large area atm ospheric Cherenkov detectors for ground-based gamma-ray astronomy. Thi s interest stems, in large part, from the fact that the gamma-ray ener gy region between 20 and 250 GeV is unexplored by any experiment. Atmo spheric Cherenkov detectors offer a possible way to explore this regio n, but large photon collection areas are needed to achieve low energy thresholds. We are developing an experiment using the heliostat mirror s of a solar power plant as the primary collecting element. As part of this development, we built a detector using four heliostat mirrors, a secondary Fresnel lens, and a fast photon detection system. In Novemb er 1994, we used this detector to record atmospheric Cherenkov radiati on produced by cosmic ray particles showering in the atmosphere. The d etected rate of cosmic ray events was consistent with an energy thresh old near 1 TeV. The data presented here represent the first detection of atmospheric Cherenkov radiation using solar heliostats viewed from a central tower.