Exact spatial extent of the 17 July 2021 deep-tail relativistic electron burst

Determine the precise spatial extent, particularly the radial size, of the localized relativistic electron burst observed at 19:41 UT on 17 July 2021 by the ELFIN mission and mapped by the SST19 magnetic field model to equatorial distances of approximately 33–36 Earth radii, accounting for mapping uncertainties that currently prevent exact sizing.

Background

ELFIN observed a very intense and latitudinally localized burst of electrons with energies up to 3 MeV at 19:41 UT, while MMS, located Earthward at ~17 RE, did not detect the burst. Using the SST19 magnetic field model, the burst’s equatorial footprint mapped from 36 to 33 RE during a ~10 s interval, suggesting a radial size of ~3 RE.

Because the burst was not observed by MMS and the mapping relied on an empirical model during dynamic substorm conditions, the authors note that the exact size cannot be precisely determined from available observations, leaving the burst’s true spatial extent unresolved.

References

Considering model uncertainty, the exact size of the burst is unknown, but we conclude that the model maps the burst beyond MMS.

— A Localized Burst of Relativistic Electrons in Earth's Plasma Sheet: Low- and High-Altitude Signatures During a Substorm  (2410.16412 - Shumko et al., 2024) in Discussion and Conclusions (paragraph estimating burst size from magnetic mapping)