The TUS Space Photodetector Relative Calibration in Flight

Abstract

The TUS experiment is aimed to study the energy spectrum and arrival direction of Ultra High Energy Cosmic Rays at E ∼ 100 EeV from the space orbit by measuring the fluorescence radiation of the Extensive Atmospheric Shower in the atmosphere. It is the first orbital telescope aimed for such measurements and is taking data since April 28, 2016. During the first turns of operation ∼20% PMTs were broken due to the HV tuning system failure. For the same reason, the properties of the remaining PMTs are changed. Relative calibration of PMT gains in flight was done and presented based on analyzing TUS background data itself. A reconstruction of EAS arrival directions is done using the relative calibration coefficients.