Optical system for the SST-1M, Cerenkov Gamma-ray Detection Telescope

Two unique Cerenkov telescopes (SST-1M) are installed at the Astronomical Institute of the CAS in Ondrejov. The telescopes are designed to study gamma rays with extremely high energy coming from sources in our Galaxy or in more distant places in the Universe. This is an international project involving scientists from the CAS, Palacký University in Olomouc and teams from Switzerland and Poland.

The optical design of SST-1M is based on the Dawies-Cotton optical design. The 4 m diameter mirror of the telescope is divided into 18 segments and a fully digital camera composed of 1296 pixels, each with a sampling rate of 250 MHz, is placed in the image plane at a distance of

5.6 m. The angular resolution of this telescope is 0.26°, with an average on-axis point spread function (PSF) of 9.8 mm (0.1°). The optical assembly includes an active mirror alignment system with two CCD cameras, which allows for the optimal alignment of the optical system.

The positioning and tracking system of the telescope is realized by two independent drive axes: azimuthal and elevation axis. With the use of correction functions, the pointing and tracking accuracy is better than

2 arc minutes. Here we present the design of the optical subsystem with performance measurements of its components, especially the mirror segments, which were partially manufactured at the Joint Optics Laboratory using CNC sub-aperture technology.