The Pulsating Aurora Imaging System (PAIPS) is being deployed at the Kola Peninsula and is aimed to conduct stereo measurements of pulsating aurora with high temporal resolution (1 ms). Photometers are lens telescopes using multi-anode PMTs as a photosensors operating in a single photon-counting mode, which provides extremely high sensitivity of the detectors. In this work we present the results of the search and analysis of the fastest emissions measured in a form of UV-microbursts. These events were found in data of the imaging photometer at the Verkhnetulomsky observatory during 2021–2023. All possible anthropogenic and atmospheric sources of UV-microbursts are excluded. The probable source of UV-microbursts are relativistic electron microbursts, which are observed in satellite experiments at the same geomagnetic latitudes and have similar temporal characteristics. Satellite electron detectors measurements demonstrate that relativistic electron microbursts appear as clusters or series of sharp peaks. The same is observed in the PAIPS photometer.

Mechanisms of formation and losses of radiation belts are the most important questions of magnetospheric physics, especially in a subsecond temporal scale. Energetic particles release their energy in the atmosphere producing fluorescent emission in characteristic wavelength bands. This emission is measurable and can be an additional information source on the spatiotemporal structure of particle fluxes and spectra. Here we present the world's first measurements of UV-microbursts during geomagnetic disturbance and pulsating aurora caused by high-energy electron precipitation. It demonstrates that fundamental questions of magnetospheric physics mentioned above can be addressed by using the optical measurements by highly sensitive photometers with high temporal resolution. Such a pho- tometer was installed at Verkhnetulomsky observatory at Kola Peninsula and measured a series of short (less than 0.5 s) pulses of emis- sion with an angular size of bright spot similar to 0.2 rad. Simultaneous measurements of high-energy electron fluxes made by the NOAA-19 satellite and fine temporal structure of geomagnetic pulsations demonstrate a magnetospheric origin of the observed events. (c) 2024 COSPAR. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

The TUS detector was a highly sensitive orbiting telescope. Due to the spacecraft’s polar orbit, the detector was able to observe the UV emission of the atmosphere above the polar auroral oval. Events with vintensity variations characteristic of pulsating auroras were detected along the equatorial boundary of the auroral oval. These variations occurred during prolonged geomagnetic disturbances. When compared to data from charged particle detectors, they revealed an increased flux of precipitating high-energy electrons with energies of more than 100 keV along with UV pulsations.

This paper presents the case study based on data processing of the high temporal resolution Pulsating Aurora Imaging Photometer System observations in the near-ultraviolet and optical measurements of all-sky cameras during one night (March 6–7, 2022). A long interval of aurora pulsations after midnight was observed and analyzed. A detailed frequency analysis, analysis of observational conditions and geomagnetic activity were carried out for this event. The day is characterized by slightly disturbed geomagnetic conditions. Characteristic two frequency pulsations are observed: main pulsation near 0.1 Hz and internal modulation with a period one order of magnitude less.

В сентябре 2021 года в обсерватории «Верхнетуломская» Полярного геофизического института был установлен оптический комплекс, включающий высокочувствительный изображающий фотометр. Детектирующая часть выполнена на основе многоанодных фотоэлектронных умножителей, что позволяет регистрировать свечение атмосферы в ближнем УФ-диапазоне (240–400 нм) с высокой чувствительностью и высоким временным разрешением (от 2.5 мкс). В работе представлены результаты частотного анализа пульсаций УФ-свечения, зарегистрированного 22 февраля 2022 года. Рассмотрены более 4 часов измерений, в течение которых наблюдаются различные пространственно-временные паттерны с квазипериодическими пульсациями. С 17:00 до 18:00 часов происходят вариации интенсивности на частотах около 1–2 Гц по всему полю зрения, с 19:00 до 21:00 часов появляется более высокочастотная компонента: 3.5–4 Гц, сочетающаяся с низкочастотными (0.3 Гц) прямоугольными импульсами.

Tracking Ultraviolet Set-up (TUS) on board the Lomonosov satellite measured the UV intensity pulsations in the auroral region. Sixty-four events with pulsations were registered during two measurement periods from 26 December 2016–10 January 2017 and 8–15 November 2017. During both periods, a high-intensity, long-duration, continuous auroral activity (HILDCAA) was detected. Simultaneous measurements in LEO by Lomonosov (DEPRON detector) and Meteor-M2 satellites show the enhanced fluxes of the trapped and precipitated energetic electrons in the region of the Earth’s outer radiation belt during these periods. We found that most of the UV-events correspond to energetic electron (E > 100 keV) precipitation. One can suggest that particles of these and higher energies cause a pulsating emission relatively deep in the atmosphere.

The Tracking Ultraviolet Setup (TUS) was the first orbital detector aimed to check the possibility of recording ultra-high energy cosmic rays (UHECRs) at E≳100 EeV by measuring the fluorescence signal of extensive air showers in the atmosphere. TUS was an experiment funded by the Russian Space Agency ROSCOSMOS, and it operated as a part of the scientific payload of the Lomonosov satellite since April 2016 till late 2017. During its mission, TUS registered almost 80,000 events in its main operation mode, with a few of them being sufficiently interesting to be more deeply scrutinized as they showed light profile and duration similar to UHECR events, even though much brighter. At the same time, the data acquired by TUS in different acquisition modes have been used to search for more exotic matter such us strangelets and nuclearites, and to measure occurrence, time profile and signal amplitude of different classes of transient luminous events among other scientific objectives, showing the interdisciplinary capability of a space-based observatory for UHECRs. In this paper, we report a selection of studies and results obtained with the TUS telescope which will be presented and placed in the contest of the present and future missions dedicated to the observation of UHECRs from space such as Mini-EUSO, K-EUSO and POEMMA.

The highly sensitive TUS telescope with high temporal resolution operated on board the Lomonosov satellite in 2016 and 2017. The detector measured UV pulsations in the auroral zone with a time resolution of 6.6 ms. Examples of joint observations by the TUS detector and all-sky cameras on the Kola Peninsula are analyzed. It is shown that the TUS field of view covered a wide region of pulsating auroras, and the fine temporal structure of pulsations is determined.

The Lomonosov satellite was launched into a 97.3° polar sun-synchronous orbit on April 26, 2016, and operated in orbit until December 2017. The TUS detector is a highly sensitive telescope, designed for both detection of ultra-high-energy cosmic rays and the Earth’s atmosphere UV-radiation in the 240–400 nm range. To measure variety of atmospheric phenomena the telescope has four modes of operation with different temporal resolutions (from 0.8 µs to 6.6 ms). Among the events recorded above 50° N in the mode with a temporal resolution of 6.6 ms, 66 were identified with an unusual spatiotemporal structure, representing local pulsations of glow in the field of view of the instrument. Geographical distribution was analyzed and it was shown that events are mainly located in the area of equatorial boundary of auroral oval (more than half of events were registered on L-shells 4–6). Characteristic frequencies of pulsations of glow intensity are of the order of 1–10 Hz, and areas of pulsating glow are localized in the space with characteristic horizontal size of 10–15 km. A comparison with the THEMIS ground-based all-sky cameras was made. 11 joint observations were found and the presence of aurora lights at the time of TUS events registration was shown by ground-based cameras, although no obvious coincidences of pulsations were found.

Observations of a faint pulsating UV emission from the atmosphere in the region of auroral oval were made by a highly sensitive satellite telescope TUS with a milliseconds temporal resolution. The TUS detector was launched in April 2016 on board the Lomonosov spacecraft. TUS was designed to register the extensive air shower (EAS) fluorescent signal from ultra-high-energy cosmic rays in the wavelength range 300-400 nm. EAS fluorescence is a weak and rapidly moving signal in the detector's field of view (FOV). Therefore, the TUS detector was equipped with a 2 m(2) mirror and high temporal resolution (0.8 mu s) photo detector. The FOV of the device is 6400 km(2), the angular resolution is 10 mrad, which corresponds to the 5 x 5 km square on the Earth surface. The Lomonosov satellite has a polar sun-synchronous orbit with an inclination of 97.3 degrees, which provides measurements up to the high latitudes on the night side of the orbit. The detector electronics implements several operating modes that differ in time resolution (from 0.8 mu s to 6.6 ms) and measure optical phenomena of different time scales. We analyze the near-UV glow in the northern polar region (50 degrees-80 degrees N), carried out in a mode with a temporal resolution of 6.6 ms and a waveform duration of 1.7 s. About 2500 observations were analyzed in a wide range of longitudes. A selection of events with the peculiar spatial-temporal dynamics of the signal was made. An analysis of the selected events structure and location relative to the auroral oval shows that fast pulsations are observed during disturbed geomagnetic conditions at the equatorial border of the auroral zone.

A technique is proposed for carrying out flight calibration of a photomultiplier tubes (PMTs) of the photodetector in the orbital TUS detector of ultra-high-energy cosmic rays in the absence of a calibration signal. The new technique consists in calculating two statistical characteristics of digitized signals from detected events (their mean value A and variance $$\sigma _{A}^{2}$$ ) and constructing the linear approximation $$\sigma _{A}^{2}$$ (A) for stationary signals. This technique has been tested in a laboratory experiment with a photodetector module, which is identical to the modules used in the detector. As a result, the gains of most photodetector channels of the TUS detector have been estimated again and the changes that occurred (in particular, the “aging effect”) have been analyzed.

A procedure for the in-flight calibration of the TUS photoreceiver is proposed and implemented, based on an analysis of stationary signal fluctuation. The procedure is tested using a laboratory mockup. New estimates of the gain are obtained for most TUS channels, and the changes that occur are analyzed.

Предложен и реализован метод полетной калибровки фотоприемника ТУС, основанный на анализе флуктуаций стационарного сигнала. Метод проверен на лабораторном макете. Получены новые оценки коэффициентов усиления большинства каналов ТУС и проанализированы произошедшие изменения.