The ASTRI camera for the Cherenkov Telescope Array

The ASTRI Dual-Mirror Small-Size Cherenkov Telescope

“…This behavior indicates a reduced telescope efficiency, that is most likely associated with mirror degradation and misalignment, which were further investigated. On the other hand, the trigger threshold was found to be higher [12] due to a local NSB higher than expected. In December 2017, 1.7 hours of gamma-ray data on the Crab Nebula and 1.4 hours of dedicated off target data were collected, respectively, resulting in a non-detection (see [21] for details) of this well-known VHE emitter.…”

“…Nevertheless, these observations allowed to verify the end-toend concept of the prototype, from the photon detection to the data analysis, with a complete data analysis report being given in [21]. The variance mode has been evaluated in January and March 2018 and showed its potential in assessing the telescope's pointing behavior [10] and checking the optical alignment of the M1 segments [12]. Indeed, the variance data indicated some misaligned M1 mirrors.…”

“…Since then, the camera underwent engineering tests, and some scientific runs were performed. First trigger rates have been recorded as function of the pixel trigger thresholds during moonless nights while pointing the telescope at different sky positions, with a topological trigger of at least five contiguous pixels [12,21]. A preliminary analysis of the curves indicated the camera's working point to be at ∼ 11 phe, meaning that the trigger rate in the region dominated by the air shower events is lower than expected from measurements previously obtained in lab.…”

“…Moreover, the primary-mirror segments have a sandwich-like structure, with an area density of about 12 kg/m 2 , making them light weight such that handling and mounting operations are easy. The ASTRI-Horn telescope design includes a novel camera design that exploits the characteristics of the telescope's SC design, leading to a very compact camera (0.52 × 0.66 × 0.56 mm; [12]). The fundamental elements of this novel design are the choice of photosensor, i.e., Silicon photomultipliers (SiPMs), and the read-out electronics.…”

“…The camera trigger is topological, meaning it is activated when a given number of contiguous pixels shows a signal above a certain threshold equivalent to a given number of photoelectrons, with both the number of contiguous pixels and the number of photoelectrons being adjustable. A particular operating mode of the read-out electronics is the so-called variance technique [12,13], for which the electric signal generated by each pixel that is not triggered by the first level trigger is continuously sampled. While the sequence of ADC (Analog to Digital Converter) values obtained is constant with time, its variance is proportional to the photon flux impinging on the pixel.…”