Calibration and Testing of the JEM-EUSO Detectors Using Stars Observed in the UV Band

The JEM-EUSO program is focused on observations of Ultra High Energy Cosmic Rays (UHECRs) from space. For this purpose, a series of detectors based on multi-anode photomultiplier tubes with a time resolution of the order of μs have been developed. The detectors work in the UV band to search for ultra-fast signals produced in the Earth's atmosphere during an Extensive Air Shower (EAS) development. Since 2014, various signals have been detected by ground-, ballon- and space-based detectors. A single photodetector module consists of a focal surface with a matrix of 36 multi-anode photomultiplier tubes containing 2304 pixels. The detector's structure allows probing it during the mission if a point-like source emitting in a UV band is in the field of view. In this work, we present the idea and results of calibration of the JEM–EUSO detectors using signals from stars registered during sky observations from the ground. Registered signals can be used for the absolute calibration of the detectors and for testing the detector condition during observations. The presented analysis is based on the data taken by the EUSO-TA and EUSO-TA2 experiments.