Performance of a 20 m diameter Cherenkov imaging telescope

In this paper, we consider the influence of the reflector design of a large multi-mirror imaging atmospheric Cherenkov telescope on the pulse shape of the light collected by the photo-receiver. As an example, we compared the response from two 20 m diameter f/1 telescopes with spherical (Davies–Cotton design) and parabolic reflectors. It is shown that the spherical reflector substantially widens the pulse of collected Cherenkov photons, while the design-induced additional widening is negligibly small for the parabolic reflector. At the detection of 10 GeV γ-showers, the pulse width on the spherical telescope's focal plane may reach 15–20 ns instead of 5–8 ns inherent to the incident light pulse itself, and is almost identical to the case with a parabolic reflector. The possibility of reducing the Cherenkov light integration gate, which is limited by the reflector's particular design, is decisive for the telescope's energy threshold lower limits.