The optical system of the Large-Sized Telescopes for the Southern Site of the Cherenkov Telescope Array Observatory

Abstract

The Cherenkov Telescope Array Observatory (CTAO) is establishing two sites: in La Palma, Canary Islands, and Paranal, Chile, to observe gamma-ray sky from 0.03 to 300 TeV with high sensitivity and resolution. It involves 70 air Cherenkov telescopes of various sizes. Four 23-meter parabolic Large-Sized Telescopes (LSTs) in the north cover 0.03-0.5 TeV; LST-1 is operational, and others are starting. In the south, Italy's INAF and INFN, funded by the European Community via the PNRR CTA+ Program, develop two LSTs to improve low-energy detection to be set at southern site. The INAF team reviewed the telescope design for southern site conditions, especially seismic loads. The Brera Observatory is responsible for the optical system, which uses 198 hexagonal mirror tiles (1.7 m) arranged in three coronas to mimic a monolithic parabola with cold glass technique. This contribution reports about the optical design and about the optical performance of the produced mirrors.