Using muon rings for the optical calibration of the ASTRI telescopes for the Cherenkov Telescope Array

摘要

High-energy muons constitute a very useful tool to calibrate the total optical throughput of any telescope of the Cherenkov Telescope Array (CTA). Differences in precision and efficiency can however be present due to the variety of telescope types and sizes. In this contribution we present some preliminary results on simulated muon ring images collected by the ASTRI small sized dual-mirror (SST-2M) telescope in the basic configuration installed in Italy at the Serra La Nave observing station. ASTRI SST-2M is able, using 6% of the detected muon events, to calibrate with muons the optical throughput down to a degradation of the optical efficiency of 30%. Moreover, its precision in reconstructing the muon arrival direction is about one camera pixel, and its error on the reconstructed ring radius is ～6.3%. The adopted procedures will be tested and validated with real data acquired by the prototype after the commissioning phase. The nine telescopes that will form the ASTRI mini-array, proposed to be installed at the final CTA southern site during the pre-production phase, will improve these results thanks to the higher detection efficiency and the lower optical cross-talk and after-pulse of their updated silicon photomultipliers.