UVscope and its application aboard the ASTRI-Horn telescope

Abstract

UVscope is an instrument, based on a multi-pixel photon detector, developed to support experimental activities for high-energy astrophysics and cosmic ray research. The instrument, working in single photon counting mode, is designed to directly measure light flux in the wavelengths range 300-650 nm. The instrument can be used in a wide field of applications where the knowledge of the nocturnal environmental luminosity is required. Currently, one UVscope instrument is allocated onto the external structure of the ASTRI-Horn Cherenkov telescope devoted to the gamma-ray astronomy at very high energies. Being co-aligned with the ASTRI-Horn camera axis, UVscope can measure the diffuse emission of the night sky background simultaneously with the ASTRI-Horn camera, without any interference with the main telescope data taking procedures. UVscope is properly calibrated and it is used as an independent reference instrument for test and diagnostic of the novel ASTRI-Horn telescope.

Evaluating the night sky background directly from the signal images detected by the ASTRI telescopes

“…The misalignment between UVscope and ASTRI-Horn, verified with pointings on several known stars (i.e. Eta Herculis, Beta Leonis and Zeta Tauri), is 0.3 • [8]. The effects of this misalignment in the comparison between ASTRI-Horn and UVscope are negligible with respect to the ones due the different working ranges.…”

“…The UVscope instrument [8] is a light detector developed at INAF/IASF-Palermo and it is mainly devoted to the measurements of the NSB light and atmosphere transparency in the wavelength band 300-650 nm. It is working in single photon counting mode that keeps negligible the electronic noise.…”

“…The data acquired by UVscope are registered, pixel by pixel, as number of counts in a pre-selected integration time (1 s). The conversion from counts to physical units is related to several features (geometrical factor, dark counts, average efficiency, gain uniformity) that characterize the sensor and its configuration, as widely detailed in [8] and briefly reported in the following. The geometrical factor corresponds to about 1.225 mm 2 ×deg 2 ; the dark counts has negligible values (0.7 counts/second per pixel) and the mean value of the global efficiency of the entire detection unit (comprehensive of collecting, trigger, quantum efficiencies and quartz windows) results in 11.61%.…”

Tools and Procedures for the ASTRI Mini-Array Calibration

“…It is essentially formed by a photon detector with its front-end and data acquisitions electronics unit working in Single Photon Counting mode, and a pinhole collimator to regulate the FoV of the detector. UVSiPM is the evolution of the UVscope instrument [10] mounted on ASTRI-Horn and whose sensor is a multianode photomultiplier. Differently from its parent, the UVSiPM sensor is a single 8×8 Silicon Photo-Multiplier unit, the same model adopted in the ASTRI Cherenkov camera; this allows to evaluate the local NSB in the same wavelength range of the ASTRI camera.…”

The ASTRI-Horn telescope: comparison with the auxiliary UVscope measurements as calibration tool.

“…Several auxiliary instruments are present on site to monitor environmental and sky conditions; among them, UVscope [6,7], a calibrated instrument devoted to the measurement of the NSB light in the wavelength range 300-650 nm. The UVscope designed for ASTRI-Horn basically consists of: a photodetector with a time resolution of 10 ns equipped with its front-end and data acquisition electronics units working in single photon counting (SPC) mode, and an interface card for computer connection; a pinhole collimator to regulate the angular aperture of the detector and to protect its sensitive area against stray light; a motorized diaphragm to open/close the entrance pupil during night/day.…”