Analysis of EAS-like events detected by the Mini-EUSO telescope

Abstract

The Mini-EUSO telescope is the first space-based detector of the JEM-EUSO program. It was launched for the International Space Station on August 22 𝑛𝑑 , 2019 to observe from the ISS orbit (∼420 km altitude) various phenomena occurring in the Earth's atmosphere through a UVtransparent window located in the Russian Zvezda Module. The dimension of the window defines and constrains the dimension of the optics, based on a set of two Fresnel lenses of 25 cm diameter each, almost two orders of magnitude smaller than the system foreseen for a larger space-based detector, like the original JEM-EUSO detector or the future POEMMA. As a consequence, the energy threshold of Mini-EUSO is very high, above 10 21 eV. Nevertheless, a series of events that resemble the shape and the time duration of EAS-induced events have been detected in Mini-EUSO data. This contribution presents the most interesting cases, showing that the vast majority of the EAS-like events can be traced back to ground sources repeatedly flashing and triggered many times by Mini-EUSO. Some non-repeated EAS-like events are also present. In these cases, it is possible to exclude their cosmic origin through the comparison with simulated events. Since it is clear that those events can not be originated by a UHECR, we decided to rename them "Short Light Transients" or SLTs. Finally, it was possible to associate some of the SLTs with atmospheric activity. This analysis confirms the validity of the JEM-EUSO detection principle and shows that it is possible for a space-based detector to distinguish between events induced by UHECRs and events with a different origin.

Use of Silicon Photomultipliers in the Detectors of the JEM-EUSO Program

“…The lens size limits the energy threshold to particles above 10 21 eV, which so far have not been observed. The algorithm worked correctly, triggering on-ground Xenon flashers [52] and ELVES [53]. The 320 µs time resolution (D2-GTU) corresponds to the sum of 128 D1-GTUs and is calculated by the PDM acquisition board.…”