Abstract Earth's magnetotail and its plasma sheet are highly dynamic, influenced by both the solar wind and the inner magnetosphere. Periodically, energy is explosively released in the magnetotail during substorms. However, the extent to which electrons are accelerated in the magnetotail remains an open question, with recent observations revealing acceleration to energies exceeding all previous theoretical and simulation estimates. Here, we investigate the possible origin and spatial scale of relativistic electron bursts by combining in situ plasma sheet measurements taken by the Magnetospheric Multiscale (MMS) mission, with low Earth orbit electron precipitation measurements taken by the Electron Losses and Fields Investigation (ELFIN). On 17 July 2021 at 19:41 UT, ELFIN detected a transient and intense burst of 3 MeV electrons precipitating into the atmospheric loss cone. These relativistic electrons had energies higher than the surrounding plasma sheet, and had fluxes higher than the nearby Van Allen radiation belt. By comparing the electron spectra between MMS and ELFIN, we suggest the burst originated from the plasma sheet, which is supported by the SST19 magnetic field model. Lastly, MMS did not directly observe the burst, despite observing the central plasma sheet at . Altogether, these results suggest that the plasma sheet may be capable of effectively accelerating electrons to relativistic energies over a localized region.
Shumko et al. (Wed,) studied this question.