Development of TUS pinhole cameras for observing transient luminous events from space and establishing role of those events as a background for ultra-high-energy cosmic-ray measurements

The TUS (tracking ultraviolet setup) experiment is intended for the observation from space of ultraviolet (UV) fluorescence induced both by ultra-high-energy cosmic rays (UHECRs) with energies above 5 × 10 19 eV and by transient luminous events (TLEs) occurring in the upper atmosphere. These two types of events are very different in terms of duration, lateral shape, and intensity; thus, each behaves as a background for the other. The TUS is equipped with two conventional pinhole cameras as auxiliary instrumentation to detect and efficiently distinguish TLEs from UHECRs. Each pinhole camera contains a MAPMT (multi-anode photo-multiplier tube) and its associated analog and digital electronics. The R11265-03-M64 MAPMT has been custom-made for space applications by Hamamatsu Photonics, particularly for the future EUSO (Extreme Universe Space Observatory) UHECR space mission. Thus, the TUS pinhole system will be the test bench for the deployment in space of a large number, ∼5000, of MAPMTs. In this study, we present the design and fabrication of the pinhole cameras, and we estimate the detectability of TLEs with respect to atmospheric light background.