Title: “Astrometric techniques for the calibration of the ASTRI Cherenkov telescope”

Seminar by Simone Iovenitti, PhD (INAF-Brera Astronomical Observatory, University of Milan).

Monday 7th of March, 15:00 p.m.

Google Meet Link: https://meet.google.com/jfi-jtfp-ybu

Abstract: “ASTRI in an Italian project for the study of Very High-Energy astrophysical phenomena up to 300 TeV and beyond. After the success of the first prototype instrument located in Italy, ASTRI-Horn, the project is entering the realization phase of the MiniArray: 9 identical Cherenkov telescopes working in stereoscopic mode to be installed in Tenerife, Canary Islands. The ASTRI telescopes present a dual-mirror Schwarzschild-Couder optical configuration (never adopted before in gamma-ray astronomy) and a Cherenkov camera based on fast SiPM sensors, able to image the nanosecond atmospheric flashes produced by energetic cosmic photons. Unfortunately, such devices are almost blind to the steady flux of stars in the field of view and consequently the calibration of their pointing represents a technological challenge, also because the compactness of the structure prevents from installing auxiliary monitoring camera sharing the same optical system of the telescope. However, exploiting the so-called Variance method (a statistical algorithm implemented in the ASTRI electronics) the star signal can be successfully recovered by ASTRI (down to ~ 7 mag), offering the potentiality to image the night sky background and meet the demanding pointing requirement (few arc-sec) despite the coarse pixel size of the camera (11 arc-min). To this end, dedicated astrometry techniques have been developed on purpose. Their validation with data from ASTRI-Horn revealed the presence of unexpected systematic errors, demonstrating the importance of such analysis. At present, similar routines for the astrometric calibration of the pointing are being developed to be implemented in the MiniArray, enhancing the accuracy of the whole system”.