Kinematics reconstruction of the EAS-like events registered by the TUS detector

TL;DR

This paper presents a new method for reconstructing the kinematic parameters of EAS-like events detected by the TUS satellite, revealing potential anthropogenic origins and aiding future cosmic ray observations.

Contribution

It introduces an advanced reconstruction technique for low-resolution space-based EAS-like events, improving accuracy in determining their kinematic parameters and origin.

Findings

All six events had out-of-space arrival directions with low zenith angles.

Reconstructed tracks correlated with airport runways and VHF stations.

Method will enhance future space missions like K-EUSO.

Abstract

The Tracking Ultraviolet Set-up (TUS) is the world's first orbital imaging detector of Ultra High Energy Cosmic Rays (UHECR) and it operated in 2016-2017 as part of the scientific equipment of the Lomonosov satellite. The TUS was developed and manufactured as a prototype of the larger project K-EUSO with the main purpose of testing the efficiency of the method for measuring the ultraviolet signal of extensive air shower (EAS) in the Earth's night atmosphere. Despite the low spatial resolution ($\sim5\times5$ km$^2$ at sea level), several events were recorded which are very similar to EAS as for the signal profile and kinematics. Reconstruction of the parameters of such events is complicated by a short track length, an asymmetry of the image, and an uncertainty in the sensitivity distribution of the TUS channels. An advanced method was developed for the determination of event kinematic parameters including its arrival direction. In the present article, this method is applied for the analysis of 6 EAS-like events recorded by the TUS detector. All events have an out of space arrival direction with zenith angles less than 40{\deg}. Remarkably they were found to be over the land rather close to United States airports, which indicates a possible anthropogenic nature of the phenomenon. Detailed analysis revealed a correlation of the reconstructed tracks with direction to airport runways and Very High Frequency (VHF) omnidirectional range stations. The method developed here for reliable reconstruction of kinematic parameters of the track-like events, registered in low spatial resolution, will be useful in future space missions, such as K-EUSO.