Abstract
This study investigates the energy spectrum of electron microbursts
observed by the Focused Investigations of Relativistic Electron Burst
Intensity, Range, and Dynamics II (FIREBIRD-II, henceforth FIREBIRD)
CubeSats. FIREBIRD is a pair of CubeSats, launched in January 2015 into
a low Earth orbit, that focus on studying electron microbursts. High
resolution electron data from FIREBIRD-II consists of 5 differential
energy channels between 200 keV and 1 MeV and a $>$1 MeV
integral channel. This covers an energy range that has not been well
studied from low Earth orbit with good energy and time resolution. This
study aims to improve understanding of the scattering mechanism behind
electron microbursts by investigating their spectral properties and
their relationship to the equatorial electron population under different
geomagnetic conditions. Microbursts are identified in the region of the
North Atlantic where FIREBIRD only observes electrons in the bounce loss
cone. The electron flux and exponential energy spectrum of each
microburst is calculated using a FIREBIRD instrument response modeled in
GEANT4 (GEometry ANd Tracking) and compared with the near equatorial
electron spectra measured by the Van Allen Probes. Microbursts occurring
when the AE index is enhanced tend to carry more electrons with
relatively higher energies. The microburst scattering mechanism is more
efficient at scattering electrons with lower energies, however the
difference in scattering efficiency between low and high energy is
reduced during periods of enhanced AE.