Performance of a wide field-of-view atmospheric Cherenkov telescope prototype based on a refractive lens

Abstract A wide field-of-view (FoV) is one of the most important goals for future ground-based γ -ray astronomy, and it is especially crucial for detailed studies of temporal and spectral characteristics of solitary events, such as γ -ray bursts (GRBs), highly variable sources like blazars, or potential very high energy (VHE) electromagnetic counterparts of gravitational waves (GWs). Atmospheric Cherenkov Telescope (ACT) based on refractive optics and operated at a very high altitude observatory may be an appropriate solution. In the present study, we report the characteristics and performance of a large FoV ACT prototype based on a refractive convex water lens. A reconstruction method for estimating the arrival direction of the air shower was developed by combining the water-lens telescope and the Extensive Air Shower (EAS) array. The Cherenkov images of the air showers were obtained by a water-lens prototype with 48 pixels, an FoV of 15 ° × 13 ° , and a median angular resolution of ∼ 0 . 9 ° .