CACTUS is a ground based Air Cherenkov Telescope (ACT) located at Solar Two near Daggett, California, and operated by the University of California, Davis. It was commissioned in its present incarnation during the Fall of 2004.
CACTUS utilizes a set of 144 heliostats, each 42 m2, to form a composite mirror with a total effective area of about 6,000 m2. Flashes of Cherenkov light produced by atmospheric air showers are detected using a secondary mirror and a camera composed of 80 photomultiplier tubes (PMTs). Some PMTs collect the light from more than one heliostat so the signals are differentiated using the unique timing of the pulses, effectively providing up to 300 independent samples of the Cherenkov wavefront. Calibration data and simulations indicate that CACTUS is detecting gamma rays with an energy of 40 GeV and higher.
The observational program of CACTUS has thus far included Pulsars/Supernova Remnants (Crab, Geminga), Active Galactic Nuclei (Mk421, Mk501) and the Dwarf Spheroidal Galaxy (Draco). Future observations are planned for Sextans, 3C279 and 3C66A.
An aeriel view of Solar Two
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