A Conjugate Study of a Localized High-Energy Precipitation Event in the Evening Sector

During a substorm occuring in the recovery phase of the geomagnetic storm of August 6th 1998 a high-energy precipitation region appeared poleward of the auroral oval in the evening sector. The event lasted a few minutes and was seen in the northern hemisphere by the X-ray and UV imagers on-board the POLAR satellite. Due to very high fluxes, good time resolution of the X-ray data was obtained. The time and spectral evolution is studied and compared with ground-based radio-wave absorption measurements which show very strong absorption ({ ~}8 dB) in both hemispheres. Ground magnetometer data and data from other sources are invoked to characterize the event. We will discuss whether it should be considered a separate injection or a localized expansion with hardening and intensification of the ongoing precipitation, and we will look into possible source mechanisms.