On the background of low threshold imaging Cherenkov telescopes induced by cosmic ray electrons

The next generation large diameter (⩾20 m) imaging atmospheric Cherenkov telescopes should allow reduction of the threshold of detection of gamma-rays down to several GeV. At such low energies, the background events can be dominated by cosmic ray electrons. In this paper we estimate the detection energy threshold of a large diameter atmospheric Cherenkov telescope with respect to the diffuse cosmic ray electrons. It is shown that the detection energy threshold of cosmic ray electron induced showers is higher than that for primary gamma showers due to the differences in the development of electromagnetic air showers initiated by these primaries. This can provide a background-free detection region for primary gamma-rays with energy E ⩽ 5–10 GeV, provided that the misclassified events induced by primary hadrons of significantly higher energies and muons are effectively suppressed.