An extensive-air-shower-like event registered with the TUS orbital detector

Abstract

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.

arXiv comment24 pages; v2: important changes to address comments by the anonymous referee; main conclusions unchanged

References in corpus (7)

• An evaluation of the exposure in nadir observation of the JEM-EUSO mission
• The TUS detector of extreme energy cosmic rays on board the Lomonosov satellite
• ESAF: Full Simulation of Space-Based Extensive Air Showers Detectors
• Mini-EUSO: A high resolution detector for the study of terrestrial and cosmic UV emission from the International Space Station
• First results from the TUS orbital detector in the extensive air shower mode
• Cosmic dust grains strike again
• Early Results from TUS, the First Orbital Detector of Extreme Energy Cosmic Rays

Cited by in corpus (9)

• Ultra-High-Energy Cosmic Rays: The Intersection of the Cosmic and Energy Frontiers
• Mini-EUSO mission to study Earth UV emissions on board the ISS
• Observation of night-time emissions of the Earth in the near UV range from the International Space Station with the Mini-EUSO detector
• Development of a cosmic ray oriented trigger for the fluorescence telescope on EUSO-SPB2
• Developments and results in the context of the JEM-EUSO program obtained with the ESAF Simulation and Analysis Framework
• Kinematics reconstruction of the EAS-like events registered by the TUS detector
• Application of neural networks to classification of data of the TUS orbital telescope
• EAS observation conditions in the SPHERE-2 balloon experiment
• Prospects of observing gamma-ray bursts with orbital detectors of ultra-high energy cosmic rays