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The origin and nature of extreme energy cosmic rays (EECRs), which have energies above the 5 ⋅ 10 19 eV —the Greisen-Zatsepin-Kuzmin (GZK) energy limit, is one of the most interesting and complicated problems in modern cosmic-ray physics. Existing ground-based detectors have helped to obtain remarkable results in studying cosmic rays before and after the GZK limit, but have also produced some contradictions in our understanding of cosmic ray mass composition. Moreover, each of these detectors covers only a part of the celestial sphere, which poses problems for studying the arrival directions of EECRs and identifying their sources. As a new generation of EECR space detectors, TUS (Tracking Ultraviolet Set-up), KLYPVE and JEM-EUSO, are intended to study the most energetic cosmic-ray particles, providing larger, uniform exposures of the entire celestial sphere. The TUS detector, launched on board the Lomonosov satellite on April 28, 2016 from Vostochny Cosmodrome in Russia, is the first of these. It employs a single-mirror optical system and a photomultiplier tube matrix as a photo-detector and will test the fluorescent method of measuring EECRs from space. Utilizing the Earth’s atmosphere as a huge calorimeter, it is expected to detect EECRs with energies above 10 20 eV . It will also be able to register slower atmospheric transient events: atmospheric fluorescence in electrical discharges of various types including precipitating electrons escaping the magnetosphere and from the radiation of meteors passing through the atmosphere. We describe the design of the TUS detector and present results of different ground-based tests and simulations.

The main goal of the TUS experiment was to search for and study extremely high-energy cosmic rays with energies EeV. The TUS detector registered a number of unusual events, the origin of which is unclear. The analysis of not similar to EAS and unique anomalous events is the subject of the study presented in this paper.

The main goal of the TUS experiment was to search for and study ultra-high energy cosmic rays with energies E > 70 EeV. The TUS detector registered a number of unusual events, the origin of which is unclear. Events that are unique and not similar to extensive air shower (EAS) are the subject of the study presented in this paper. Events such as gamma-ray bursts (GRBs), out-of-aperture upward going EASs accompanied by lightning flashes, as well as terrestrial gamma-ray flashes (TGFs) are considered as their possible sources.

The main goal of the TUS experiment was to search for and study ultra high-energy cosmic rays with energies E > 70 EeV. The TUS detector registered a number of unusual events, the origin of which is unclear. Events that are unique and not similar to EAS are the subject of the study presented in this paper. Events such as gamma-ray bursts (GRBs), out-of-aperture upward going EASs accompanied by lightning flashes, as well as terrestrial gamma-ray flashes (TGFs) are considered as their possible sources.

The results of the TUS experiment on search and study ultra high-energy cosmic rays with energies E > 70 EeV are analyzed. The TUS detector registered several unusual events of the unclear origin. The analysis of not similar to EAS and unique anomalous events is the subject of the study presented in this paper.

TAIGA array addresses gamma-ray astronomy at energies from a few TeV to several PeV as well as cosmic ray physics from 100 TeV to several EeV. A 1 km2 TAIGA setup will consist of 120 wide-angle detectors of the Cherenkov timing array TAIGA-HiSCORE and three imaging air Cherenkov telescopes with the field of view diameter of 9.6°. In this paper, first experimental results of the first operation stage are presented: signal detection from two gamma-ray sources, the Crab Nebula and Markarian 421, by the first IACT in stand-alone mode. The detected signal is shown to be in agreement with the Monte Carlo expectation. In future, gamma-ray signal will be detected by a larger number of TAIGA telescopes as well as the TAIGA-HiSCORE array, that is, in combined operation mode.

TUS (Tracking Ultraviolet Set-up) is the world's first orbital detector of ultra-high-energy cosmic rays (UHECRs). It was launched into orbit on 28th April 2016 as a part of the scientific payload of the Lomonosov satellite. The main aim of the mission was to test the technique of measuring the ultraviolet fluorescence and Cherenkov radiation of extensive air showers generated by primary cosmic rays with energies above ~100 EeV in the Earth atmosphere from space. During its operation for 1.5 years, TUS registered almost 80,000 events with a few of them satisfying conditions anticipated for extensive air showers (EASs) initiated by UHECRs. Here we discuss an event registered on 3rd October 2016. The event was measured in perfect observation conditions as an ultraviolet track in the nocturnal atmosphere of the Earth, with the kinematics and the light curve similar to those expected from an EAS. A reconstruction of parameters of a primary particle gave the zenith angle around 44\\(^\\circ\\) but an extreme energy not compatible with the cosmic ray energy spectrum obtained with ground-based experiments. We discuss in details all conditions of registering the event, explain the reconstruction procedure and its limitations and comment on possible sources of the signal, both of anthropogenic and astrophysical origin. We believe this detection represents a significant milestone in the space-based observation of UHECRs because it proves the capability of an orbital telescope to detect light signals with the apparent motion and light shape similar to what are expected from EASs. This is important for the on-going development of the future missions KLYPVE-EUSO and POEMMA, aimed for studying UHECRs from space.

TUS (Tracking Ultraviolet Set-up), the first orbital detector of extreme energy cosmic rays (EECRs), those with energies above 50 EeV, was launched into orbit on April 28, 2016, as a part of the Lomonosov satellite scientific payload. The main aim of the mission is to test a technique of registering fluorescent and Cherenkov radiation of extensive air showers generated by EECRs in the atmosphere with a space telescope. We present preliminary results of its operation in a mode dedicated to registering extensive air showers in the period from August 16, 2016, to November 4, 2016. No EECRs have been conclusively identified in the data yet, but the diversity of ultraviolet emission in the atmosphere was found to be unexpectedly rich. We discuss typical examples of data obtained with TUS and their possible origin. The data is important for obtaining more accurate estimates of the nocturnal ultraviolet glow of the atmosphere, necessary for successful development of more advanced orbital EECR detectors including those of the KLYPVE (K-EUSO) and JEM-EUSO missions.

The origin and nature of extreme energy cosmic rays (EECRs), which have energies above the 50 EeV, the Greisen-Zatsepin-Kuzmin (GZK) energy limit, is one of the most interesting and complicated problems in modern cosmic-ray physics. Existing ground-based detectors have helped to obtain remarkable results in studying cosmic rays before and after the GZK limit, but have also produced some contradictions in our understanding of cosmic ray mass composition. Moreover, each of these detectors covers only a part of the celestial sphere, which poses problems for studying the arrival directions of EECRs and identifying their sources. As a new generation of EECR space detectors, TUS (Tracking Ultraviolet Set-up), KLYPVE and JEM-EUSO, are intended to study the most energetic cosmic-ray particles, providing larger, uniform exposures of the entire celestial sphere. The TUS detector, launched on board the Lomonosov satellite on April 28, 2016, from Vostochny Cosmodrome in Russia, is the first of these. It employs a single-mirror optical system and a photomultiplier tube matrix as a photo-detector and will test the fluorescent method of measuring EECRs from space. Utilizing the Earth's atmosphere as a huge calorimeter, it is expected to detect EECRs with energies above 100 EeV. It will also be able to register slower atmospheric transient events: atmospheric fluorescence in electrical discharges of various types including precipitating electrons escaping the magnetosphere and from the radiation of meteors passing through the atmosphere. We describe the design of the TUS detector and present results of different ground-based tests and simulations.

A wide-angle Cerenkov array TAIGA-HiSCORE (FOV \\(\\)0.6 sr), was originally created as a part of TAIGA installation for high-energy gamma-ray astronomy and cosmic ray physics. Array now consist on nearly 100 optical stations on the area of 1 km\\(^2\\). Due to high accuracy and stability (\\(\\)1 ns) of time synchronization of the optical stations the accuracy of EAS arrival direction reconstruction is reached 0.1\\(^o\\). It was proven that the array can also be used to search for nanosecond events of the optical range. The report discusses the method of searching for optical transients using the HiSCORE array and demonstrates its performance on a real example of detecting signals from an artificial Earth satellite. The search for this short flares in the HiSCORE data of the winter season 2018--2019 is carried out. One candidate for double repeater has been detected, but the estimated probability of random simulation of such a transient by background EAS events is not less than 10%, which does not allow us to say that the detected candidate corresponds to a real astrophysical transient. An upper bound on the frequency of optical spikes with flux density of more than \\(10^-4 erg/s/cm^2\\) and a duration of more than 5\\,ns is established as \\( 2 10^-3\\) events/sr/hour.