X ray spectral images of energetic electrons precipitating in the auroral zone

X rays from the Earth's auroral zone are produced by the precipitation of electrons with kilovolt energies. We have used an imaging X ray spectrometer to observe this radiation over a ∼500-km field of view divided into 16 pixels. The observations were made by an experiment on the S81-1 satellite (SEEP: Stimulated Emission of Energetic Particles) during June 1982. Using high spectral resolution 4- to 40-keV X ray data, we have calculated the flux and spectral slope of the precipitating electrons. We have conducted, for the first time, a systematic survey of the characteristics of electrons spectra in a large number of individual X ray features. Most of the precipitation is confined to well-defined locations, arcs or isolated patches, separated by regions where no X ray flux was detected. Narrow features are typical for energetic electrons above 5 keV, in contrast to lower-energy electrons, which may produce relatively diffuse optical images. These X ray images have produced two-dimensional maps of precipitation which show no trends of spectral hardness with position, while on the same spatial scales there are order of magnitude changes in the flux of precipitating electrons. copyright American Geophysical Union 1988