The ASTRI contribution to the Cherenkov Telescope Array: mirror production for the SST-2M ASTRI and the MST telescopes

Abstract

The Cherenkov Telescope Array (CTA) will be the next generation ground-based observatory for gamma-ray astronomy at very-high energies. It will consist of over a hundred telescopes of different sizes (small, medium, and large) located in the northern and southern hemispheres. The Italian National Institute of Astrophysics (INAF) contributes to CTA through the ASTRI project (Astrofisica con Specchi a Tecnologia Replicante Italiana), whose main aim is to provide a series of dual-mirror small-sized telescopes (SST-2M ASTRI) and the mirrors for the single-mirror design of the medium-sized telescopes (MST). Both the primary mirror of the SST-2M ASTRI and the mirror of the MST are segmented, and such segments are realized with cold-slumping technology already used for the mirror facets of MAGIC, a system of two Cherenkov telescopes operating on the Canary Island of La Palma. On the other hand, the secondary mirror of the SST-2M ASTRI is monolithic and is realized with hot-slumping technology. Currently, we have completed the mirror production for nine SST-2M ASTRI telescopes, which will form the so-called ASTRI Mini-Array. Moreover, we have almost completed also the production of mirrors for two MSTs. In this paper, we present the mirror designs and describe the qualification activities that were performed to assess and consolidate the production process. Moreover, we report on the quality assurance approach we adopted to monitor and verify the production reliability. Finally, we present the performance of the produced mirrors and discuss their compliance with the CTA requirements.