Update on the characterisation of the pGCT, a prototype of 4m dual-mirror Cherenkov Telescope

Abstract

The Gamma-ray Cherenkov Telescope prototype (pGCT) is a prototype of an Imaging Atmospheric Cherenkov Telescope, developed as Small-Sized Telescope (SST) of 4m during the preparation of the Cherenkov Telescope Array (CTA). Based on a Schwarzschild-Couder dual-mirror optical design aiming to provide an optimised Point Spread Function (PSF) on a wide field, it had its first Cherenkov light on the Meudon site of the Observatoire de Paris in 2015. Since the decision of CTA to harmonize its future SSTs, the pGCT instrument and the experience gained with its development are now used by the Observatoire de Paris team to provide a test bench for Cherenkov astronomy and a pedagogical tool for educational purposes in Meudon. This paper briefly describes the design of the pGCT and presents the latest advances in the optics of the prototype and its characterisation, directly related to the implementation of new high-quality metallic mirrors carried out since 2020.