Abstract
The First G-APD Cherenkov Telescope (FACT) is designedto detect cosmic gamma-rays with energies from several hundred GeV upto about 10 TeV using the Imaging Atmospheric Cherenkov Technique. Incontrast to former or existing telescopes, the camera of the FACTtelescope is comprised of solid-state Geiger-mode AvalanchePhotodiodes (G-APD) instead of photomultiplier tubes for photodetection. It is the first full-scale device of its kind employingthis new technology. The telescope is operated at the Observatorio delRoque de los Muchachos (La Palma, Canary Islands, Spain) since fall2011. This paper describes in detail the design, construction andoperation of the system, including hardware and softwareaspects. Technical experiences gained after one year of operation arediscussed and conclusions with regard to future projects are drawn.
Highlights
For more than two decades, Imaging Atmospheric Cherenkov Telescopes (IACT) have been very successful in observing cosmic gamma-ray sources at very high energies (VHE, about 50 GeV to 100 TeV) [1]
In contrast to former or existing telescopes, the camera of the First G-APD Cherenkov Telescope (FACT) telescope is comprised of solid-state Geiger-mode Avalanche Photodiodes (G-APD) instead of photomultiplier tubes for photo detection
The telescope is operated at the Observatorio del Roque de los Muchachos (La Palma, Canary Islands, Spain) since fall 2011
Summary
For more than two decades, Imaging Atmospheric Cherenkov Telescopes (IACT) have been very successful in observing cosmic gamma-ray sources at very high energies (VHE, about 50 GeV to 100 TeV) [1]. To detect variability on long time scales and understand the flaring behavior of AGN, continuous monitoring for several months or years is necessary This can be achieved by robust and small telescopes [2], complementary to the large-scale arrays serving many tasks. Geiger-mode Avalanche Photodiodes (G-APD, notation used in this paper for entire sensor subdivided in cells) have the potential to replace PMTs in gamma-ray astronomy They offer a high gain (105 to 106) and can be operated under much brighter light conditions allowing observations during moon time. The system has been running almost every night since and several source observations have already been conducted for its commissioning
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