Mini-EUSO is a small, near-UV telescope observing the Earth and its atmosphere from the International Space Station. The time resolution of 2.5 microseconds and the instantaneous ground coverage of about 320 × 320 km2 allows it to detect some Transient Luminous Events, including Elves. Elves, with their almost circular shape and a radius expanding in time form cone-like structures in space-time, which are usually easy to be recognised by the eye, but not simple to filter out from the myriad of other events, many of them not yet categorised. In this work, we present a fast and efficient approach for detecting Elves in the data using a 3D CNN-based one-class classifier.

Mini-EUSO is a wide Field-of-View (FoV, 44◦) telescope currently in operation from a nadia-facing UV-transparent window in the Russian Zvezda module on the International Space Station (ISS). It is the first detector of the JEM-EUSO program deployed on the ISS, launched in August 2019. The main goal of Mini-EUSO is to measure the UV emissions from the ground and atmosphere, using an orbital platform. Mini-EUSO is mainly sensitive in the 290-430 nm bandwidth. Light is focused by a system of two Fresnel lenses of 25 cm diameter each on the Photo- Detector-Module (PDM), which consists of an array of 36 Multi-Anode Photomultiplier Tubes (MAPMTs), for a total of 2304 pixels working in photon counting mode, in three different time resolutions of 2.5 μs, 320 μs, 40.96 ms operation in parallel. In the longest time scale, the data is continuously acquired to monitor the UV emission of the Earth. It is best suited for the observation of ground sources and therefore has been used for the observational campaigns of the Mini-EUSO. In this contribution, we present the assembled UV flasher, the operation of the field campaign and the analysis of the obtained data. The result is compared with the overall efficiency computed from the expectations which takes into account the atmospheric attenuation and the parameterization of different effects such as the optics efficiency, the MAPMT detection efficiency, BG3 filter transmittance and the transparency of the ISS window.

The Extreme Universe Space Observatory on a Super Pressure Balloon 2 (EUSO-SPB2) experiment is a pathfinder mission for future space-based instruments targeting the fluxes of Ultra-High Energy Cosmic Rays (UHECR), with energies exceeding 1EeV and very high energy diffuse and transient neutrinos, with energies exceeding 1PeV. Using two telescope designs: the Fluorescence Telescope (FT) and the Cherenkov Telescope (CT), EUSO-SPB2 made novel observations of the backgrounds relevant for space-based detection. EUSO-SPB2 will launch from Wanaka, NZ in Spring of 2023, for a long duration (up to 100d) flight at a nominal float altitude of 33km. In this contribution, we will focus on the CT’s capability to measure cosmic rays from above Earth’s limb via the Cherenkov emission produced by the resultant Extensive Air Showers (EAS). Using the EASCherSim optical Cherenkov generation code, we provide an updated estimate of the event rate of above-the-limb cosmic rays for the CT, taking into account updated values for the trigger efficiency as determined during the field testing of the instrument. We take particular care to consider the longitudinal development of EAS in rarefied atmosphere, accounting for the energy dependent elongation rate. In addition, we consider improvements to the magnetic field modeling present in EASCherSim and illustrate their impact on the observed events and detection thresholds. Finally, we compare these simulations to preliminary flight data from EUSO-SPB2.

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 22nd, 2019 to observe from the ISS orbit (∼420 km altitude) various phenomena occurring in the Earth’s atmosphere through a UV-transparent 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 1021 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.

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.

The detection of astrophysical neutrinos by IceCube in the TeV-PeV energy range motivates the development of instruments for observing these particles at higher energies. Moreover, the detection of very-high-energy (VHE) neutrinos could potentially bring constraints on ultra-high energy cosmic rays (UHECRs) source models. Tau neutrinos skimming the Earth under a shallow angle can be detected through the decay of a tau resulting in an extensive air shower (EAS) in the atmosphere. The EAS can be detected by capturing some of the optical Cherenkov signal originating from the EAS particles. To assess the feasibility of the Earth-skimming technique from high altitudes, we developed a Cherenkov telescope which will be deployed on the Extreme Universe Space Observatory Super Pressure Balloon 2 (EUSO-SPB2) flew from Wanaka, NZ, on May 13th. It is a precursor for the Probe of Extreme Multi-Messenger Astrophysics. The 1 m diameter Cherenkov telescope for EUSO-SPB2 had a focal plane comprised of 512 silicon photomultipliers (SiPMs) covering a 6.4 x 12.8 square degree field of view coupled to a 100 MS/s readout based on the GET switch capacitor ring sampler. We discuss the calibration and commissioning of the telescope and its in-flight performance.

The Extreme Universe Space Observatory on a Super Pressure Balloon 1 (EUSO-SPB1) was launched in 2017 April from Wanaka, New Zealand. The plan of this mission of opportunity on a NASA super pressure balloon test flight was to circle the southern hemisphere. The primary scientific goal was to make the first observations of ultra-high-energy cosmic-ray extensive air showers (EASs) by looking down on the atmosphere with an ultraviolet (UV) fluorescence telescope from suborbital altitude (33 km). After 12 days and 4 h aloft, the flight was terminated prematurely in the Pacific Ocean. Before the flight, the instrument was tested extensively in the West Desert of Utah, USA, with UV point sources and lasers. The test results indicated that the instrument had sensitivity to EASs of ⪆3 EeV. Simulations of the telescope system, telescope on time, and realized flight trajectory predicted an observation of about 1 event assuming clear sky conditions. The effects of high clouds were estimated to reduce this value by approximately a factor of 2. A manual search and a machine-learning-based search did not find any EAS signals in these data. Here we review the EUSO-SPB1 instrument and flight and the EAS search.

The Extreme Universe Space Observatory on a Super Pressure Balloon 2 (EUSO-SPB2), successfully launched from Wanaka, New Zealand on May 13, 2022, is a precursor for a space-based astroparticle observatory such as the Probe Of Extreme Multi-Messenger Astrophysics (POEMMA). EUSO-SPB2 flew two custom telescopes. Both have UV/UV-visible sensitivity and feature Schmidt optics. The Fluorescence Telescope (FT) measures ultra-high energy cosmic rays by looking down. The Čerenkov Telescope (CT) searches for neutrino signatures by looking toward Earth’s limb. The two telescopes each have a 1 m diameter entrance pupil and segmented glass mirrors that collect light from extensive air showers at the PeV and EeV-scale. Here we describe the FT telescope optics together with the results of the FT field tests at the Utah Telescope Array (TA) site from August/September 2022. The FT recorded the night sky background, lasers, and artificial point sources. The field tests included an absolute photometric calibration of the FT telescope that is compared to a piece-wise laboratory calibration.

The Extreme Universe Space Observatory on a Super Pressure Balloon II (EUSO-SPB2) launched from Wanaka, New Zealand on May 13th 2023. Consisting of two optical telescopes, EUSOSPB2 aimed to search for very high energy neutrinos (E>PeV) via Cherenkov radiation, and ultra high energy cosmic rays (UHECRs, E>EeV) via ultraviolet fluorescence. Building on the EUSO-Balloon (2014) and EUSO-SPB1 (2017) missions, the Fluorescence Telescope (FT) comprises 108 multi-anode photomultiplier tubes at the focus of a one meter entrance diameter Schmidt telescope. The FT pointed down at the atmosphere below the SPB’s altitude of 33 km. The mission duration was planned to reach up to 100 days. Prior to flight, the instrument was extensively tested in the laboratory and in the field. These measurements, combined with simulations led to an expected peak energy sensitivity around 3 EeV. Combined with a three-times-larger field-of-view than previous EUSO balloon missions, this resulted in an expected observation rate of one UHECR shower per ten hours of observation. The FT was expected to perform the first measurement of UHECRs via fluorescence from sub-orbital space, but was unable to, due to a shortened flight. Nonetheless, these observations of EUSO-SPB2 serve as a stepping stone to future satellite-based missions, such as the Probe of Extreme Multi-Messenger Astrophysics (POEMMA), with enormous exposure to the highest energy cosmic rays with all sky coverage. In this contribution we will discuss the performance of the FT in flight as well as preliminary results.

Mini-EUSO is the first mission of the JEM-EUSO program on board the International Space Station. It was launched in August 2019 and it is operating since October 2019 being located in the Russian section (Zvezda module) of the station and viewing our planet from a nadir-facing UV-transparent window. The instrument is based on the concept of the original JEM-EUSO mission and consists of an optical system employing two Fresnel lenses of 25 cm each and a focal surface composed of 36 Multi-Anode Photomultiplier tubes, 64 channels each, for a total of 2304 channels with single photon counting sensitivity and an overall field of view of 44×44◦. Mini-EUSO can map the night-time Earth in the near UV range (predominantly between 290 nm and 430 nm), with a spatial resolution of about 6.3 km and different temporal resolutions of 2.5 μs, 320 μs and 41 ms. Mini-EUSO observations are extremely important to better assess the potential of a space-based detector in studying Ultra-High Energy Cosmic Rays (UHECRs) such as K-EUSO and POEMMA. In this contribution we focus the attention on the results of the UV measurements and we place them in the context of UHECR observations from space, namely the estimation of exposure.