Research Article

The detection of ultra-relativistic electrons in low Earth orbit

¹ Royal Observatory of Belgium, Solar-Terrestrial Centre of Excellence, Avenue Circulaire 3, 1180 Uccle, Belgium
² Royal Belgian Institute for Space Aeronomy, Solar-Terrestrial Centre of Excellence, Ringlaan 3, 1180 Uccle, Belgium
³ Université Catholique de Louvain (UCL), Centre for Space Radiations (CSR), Earth and Life Institute (ELI), Place Louis Pausteur 3, bte L4.03.08, B-1348 Louvain-La-Neuve, Belgium

^* Corresponding author: katsiyannis@oma.be

Received: 6 June 2017
Accepted: 8 December 2017

Abstract

Aims. To better understand the radiation environment in low Earth orbit (LEO), the analysis of in-situ observations of a variety of particles, at different atmospheric heights, and in a wide range of energies, is needed. Methods. We present an analysis of energetic particles, indirectly detected by the large yield radiometer (LYRA) instrument on board ESA's project for on-board autonomy 2 (PROBA2) satellite as background signal. Combining energetic particle telescope (EPT) observations with LYRA data for an overlapping period of time, we identified these particles as electrons with an energy range of 2 to 8 MeV. Results. The observed events are strongly correlated to geo-magnetic activity and appear even during modest disturbances. They are also well confined geographically within the L = 4–6 McIlwain zone, which makes it possible to identify their source. Conclusions. Although highly energetic particles are commonly perturbing data acquisition of space instruments, we show in this work that ultra-relativistic electrons with energies in the range of 2–8 MeV are detected only at high latitudes, while not present in the South Atlantic Anomaly region.