Particle and field characteristics of broadband electrons observed by the FAST satellite during geomagnetic storms

Broadband electrons represent remarkable flux enhancements of precipitating electrons over a broad energy range of 30eV-30keV near the equatorward edge of the aurora oval during geomagnetic storms. These flux enhancements were initially reported using particle data of the DMSP satellites, which did not measure pitch angle distribution of precipitating electrons. Here, we investigate broadband electrons using data from the FAST satellite. Sixteen events of broadband electrons were identified from the electron energy spectra for large geomagnetic storms between September 1996 and March 2004. We analyzed in detail energy, pitch angle distribution, and wave spectra during the broadband electron event of July 15, 2000, observed at an altitude of ~2000 km. This event was observed at ~ 10 minutes after the onset of a substorm during the main phase of a storm. The broadband electrons were not observed in one orbit (~ 133 min.) before and after the event at the same local time. These results suggest rapid particle acceleration occurring in the inner magnetosphere associated with a storm-time substorm. During this event, electron flux parallel to the local magnetic field tends to be higher than the perpendicular flux at a low energy range below 1 keV, suggesting parallel acceleration of low energy electrons at low altitudes near the satellite. At a high energy range above 1 keV, electron fluxes show isotropic or double loss-cone features. In the presentation, we show further details of the distribution function of broadband electrons and field characteristics.