Small Size Air-Cherenkov Telescopes for Ground Detection Arrays - a Possible Future Extension?

The combined use of air-Cherenkov telescopes with ground based particle detectors is investigated. While a hybrid detection technique using fluorescence telescopes and ground arrays has been successfully applied by the Pierre Auger Observatory, this study focuses on the combination of air-Cherenkov telescopes and ground arrays for detection of TeV gamma-rays. After the successful measurement of air showers with the 7-pixel prototype telescope, an upgraded version (FAMOUS) of a combined fluorescence and air-Cherenkov telescope is now operational. It employs a 55 cm aperture Fresnel-lens in a sealed tube and a 61-pixel camera with semiconductor photo sensors (SiPM). For joint measurements, it will be synchronized with the High Altitude water-Cherenkov gamma-ray observatory HAWC (Sierra Negra, Mexico) to evaluate its prospects as an enhancement of ground based detectors. A main focus is the improvement of the energy resolution by accessing complementary shower informations with both technologies. The direct measurement of the air shower particles by the HAWC observatory also allows the characterization of the air-Cherenkov telescope, such as collection area, without any Monte Carlo simulation. Preliminary results from this study will be presented and the future potential of air-Cherenkov telescopes as an extension for ground based arrays will be discussed.