Fast near-UV radiation pulsations measured by the space telescope TUS in the auroral region

Abstract

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 m2 mirror and high temporal resolution (0.8 μs) photo detector. The FOV of the device is 6400 km2, the angular resolution is 10 mrad, which corresponds to the 5×5 km square on the Earth surface. The Lomonosov satellite has a polar sun-synchronous orbit with an inclination of 97.3∘, 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 μs to 6.6 ms) and measure optical phenomena of different time scales.We analyze the near-UV glow in the northern polar region (50°–80° 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.