Characteristics of Energetic Electrons Near Active Magnetotail Reconnection Sites: Statistical Evidence for Local Energization

Abstract

Magnetic reconnection is a universal process where energy is transferred from magnetic fields to particles. However, it remains unclear whether this transfer of energy includes the direct energization of particles to high energies (i.e., >10s of keV). We compare the spectral indices of energetic (50–200 keV) electrons from six magnetotail electron diffusion region candidates encountered by MMS with those from “quiet-time” plasma sheet crossings to test whether energetic electron enhancements result from direct energization at/near the reconnection site or simply focusing high-energy populations that do not originate from the nearby X-line and already exist in the plasma sheet along the newly reconnected field lines. The study suggests that active reconnection can be a source of localized electron energization. However, the EDR spectra are not outside the range of those from the quiet-time plasma sheet, which surprisingly still often have very energetic (up to and beyond 200 keV) electrons present.