Relativistic and Ultra-Relativistic Electron Bursts in Earth's Magnetotail Observed by Low-Altitude Satellites

TL;DR

This paper reports the observation of relativistic electron bursts in Earth's magnetotail, showing that magnetic reconnection can accelerate electrons to several MeV, exceeding previous estimates, with data from low-altitude CubeSats.

Contribution

It provides the first observational evidence of relativistic electron bursts in the magnetotail using low-altitude satellite data, highlighting higher acceleration efficiencies than previously thought.

Findings

Relativistic electron bursts observed far poleward of the outer radiation belt.

Electron energies up to several MeV detected during substorms.

Power-law energy spectra characterize the bursts.

Abstract

Earth's magnetotail, a night-side region characterized by stretched magnetic field lines and strong plasma currents, is the primary site for the release of magnetic field energy and its transformation into plasma heating and kinetic energy plus charged particle acceleration during magnetic reconnection. In this study, we demonstrate that the efficiency of this acceleration can be sufficiently high to produce populations of relativistic and ultra-relativistic electrons, with energies up to several MeV, which exceeds all previous theoretical and simulation estimates. Using data from the low altitude ELFIN and CIRBE CubeSats, we show multiple events of relativistic electron bursts within the magnetotail, far poleward of the outer radiation belt. These bursts are characterized by power-law energy spectra and can be detected during even moderate substorms.