The Mini-EUSO telescope on board the International Space Station: first results in view of UHECR measurements from space

Abstract

Mini-EUSO is a telescope launched on board the International Space Station in 2019 and currently located in the Russian section of the station and viewing our planet from a nadir-facing UVtransparent window in the Zvezda module. The instrument is based on an optical system employing two Fresnel lenses and a focal surface composed of 36 Multi-Anode Photomultiplier tubes, 64 channels each, with single photon counting sensitivity and an overall field of view of 44 • . Main scientific objectives of the mission are the search for nuclearites and Strange Quark Matter, the study of atmospheric phenomena such as Transient Luminous Events, meteors and meteoroids, and the observation of sea bioluminescence. Mini-EUSO can map the night-time Earth in the near UV range (predominantly between 290 -430 nm), with a spatial resolution of about 6.3 km and different temporal resolutions of 2.5 s, 320 s and 41 ms. Mini-EUSO observations are extremely important to assess the potential of a space-based detector of Ultra-High Energy Cosmic Rays (UHECRs) such as K-EUSO and POEMMA. In this contribution we describe the detector and show preliminary results in the context of UHECR observations from space. In particular, it is shown that the typical UV nightglow background level is comparable to what was originally estimated for a space-based detector looking down to Earth. The adaptive trigger logic successfully keeps the spurious trigger rate at the designed level of ∼1 Hz in nominal conditions and in presence of quasi-static bright sources such as city lights. The logic triggers on UV transients in the s time scale due to anthropogenic light sources, such as flashers. These signals can clearly be distinguished from Extensive Air Shower (EAS) events by comparing them with simulated EASs. In addition, they demonstrate the capability of a large space-based detector such as K-EUSO or POEMMA to detect UHECRs above a few times 10 19 eV. The presence of clouds can be clearly recognized by the UV camera in many situations, which is helpful for the calculation of the exposure and for the determination of the atmospheric conditions in case of detection of an EAS. *** 27th European Cosmic Ray Symposium -ECRS *** *** 25-29 July 2022 *** *** Nijmegen, the Netherlands ***