The ASTRI-Horn Cherenkov Telescope. Technical assessment and calibrations following its refurbishment for the ASTRI Mini-Array and CTA-SST pathfinder

The ASTRI-Horn telescope is a prototype Imaging Atmospheric Cherenkov Telescope (IACT) developed within the Astrofisica con Specchi a Tecnologia Replicante Italiana (ASTRI) project. It represents the first implementation of a dual-mirror Schwarzschild–Couder (SC) optical configuration for ground-based gamma-ray IACT observations. It also served as a testbed for the Small-Sized Telescopes (SSTs) of the Cherenkov Telescope Array Observatory (CTAO) that will host at least 37 SSTs at the Paranal site in Chile, and for the forthcoming ASTRI Mini-Array. Installed in 2014 at the INAF “M.C. Fracastoro” observing station on Mount Etna, the telescope is equipped with a SiPM-based Cherenkov camera and a complete control and data acquisition system. Between 2020 and 2022, after the demonstration of the validity of the SC configuration in observing gamma-ray sources, ASTRI-Horn underwent refurbishment activities that included mirror replacement, new optical coatings, camera upgrades, and software improvements. The telescope has since been re-validated through calibration campaigns and observational tests, including the detection and spectral characterization of the Crab Nebula at TeV energies. The results confirm the correct operation of the optical system, camera electronics, and data processing chain, providing a consolidated basis for the design and development of the ASTRI Mini-Array and future CTAO-SST telescopes.