On the accuracy of determination of fluxes and energy spectra of primary gamma rays by a single imaging atmospheric Cherenkov telescope

Abstract

The strong energy dependence of the detection efficiency of gamma -rays by imaging atmospheric Cherenkov telescopes (IACT) both at the hardware and software levels, leads to significant uncertainties in the estimate of primary gamma -ray fluxes. Nevertheless, detailed Monte Carlo calculations of the principal characteristics of IACTS, in particular of collection areas and of the gamma /proton separation efficiency, allow a rather high accuracy in the evaluation of the absolute gamma -ray fluxes and in the determination of the spectral index of power-law spectra. However, the poor energy resolution of a single IACT does not permit us to distinguish features such as sharp cutoffs in primary gamma -ray spectra unambiguously. Extended sources cause additional problems in the separation and determination of the gamma -ray flux.