GAW (Gamma Air Watcher) experiment.
GAW is an array of Atmospheric Imaging Cherenkov Telescopes composed by 3 identical telescopes disposed at the vertexes of an equilateral triangle of 80 m side. GAW will operate at 2150 meters a.s.l in Calar Alto on Sierra Nevada mountains (Spain). An artistic map of the three GAW units in Calar Alto is show below. A first substantial difference between GAW and all existing and planned Cherenkov observatories is its optical system. GAW will image incident radiation with refractive optical elements instead of classical mirrors: a non-commercial Fresnel lens of 2.13 m diameter. A second fundamental difference is in the detector working mode. The focal surface detector of each telescope consists of an array of multi-anode photomultipliers (MAPMT) operated in single photoelectron counting mode. In such working mode, the electronics noise and the MAPMT gain differences are kept negligible allowing lowering the energy threshold in spite of the relatively small dimension of the telescope Cherenkov light-collector.
