A simulation of high-energy gamma-ray observations with imaging Cherenkov telescopes at high altitudes

The performance of a single gamma-ray telescope is discussed based on the Imaging Atmospheric Cherenkov Technique (IACTech) at high altitudes. Observations at a high altitude are quite suitable for the IACTech because the density of Cherenkov light caused by gamma-rays is several-times larger than at sea level. To observe gamma-ray pulsars at high altitude, a gamma-ray camera, designated Chess (Cherenkov light detecting System on Subaru) based on the IACTech, has been developed for the Subaru infrared-optical telescope at an altitude of 4200 m. Using Chess, the Crab nebula/pulsar was observed for three days in December 2001. From a comparison between the simulated and observed shower events, it was found that the night-sky background (N.S.B.) and muon showers have significant effects on the detection rate below 80 GeV in spite of the small field of view (FOV) of Chess (0.75degrees). The simulated spectrum, which includes muon shower events, is consistent with the observed spectrum. Based on this study, the performance of a camera with a larger FOV of 3.0degrees is discussed. Although the effects of muon showers and the N.S.B. become serious, the simulation results indicate that an 8.2 m Imaging Atmospheric Cherenkov Telescope (IACT) with a FOV of 3.0degrees at an altitude of 4200 m could detect 15 GeV energy gamma-rays. (C) 2004 Elsevier B.V. All rights reserved.