Application of X-ray imaging techniques to auroral monitoring

The precipitation of energetic particles into the ionosphere produces bremsstrahlung X-rays and K-alpha line emission from excited oxygen and nitrogen. If viewed from a spacecraft in a highly elliptical polar orbit, this soft (0.3 - 3.0 keV) X-radiation will provide an almost uninterrupted record of dayside and nightside auroras. A grazing incidence X-ray telescope especially designed for such auroral monitoring is described. High photon collection efficiency will permit exposure times of approximately 100 seconds during substorms. Spectrophotometry will allow users to derive the energy spectrum of the precipitating particles. If placed in a 15 earth-radius orbit, the telescope can produce auroral X-ray images with 30 km resolution. Absolute position of X-ray auroras can be established with a small optical telescope co-aligned with the X-ray telescope. Comparison of X-ray and optical images will establish the height and global distribution of X-ray aurorae, relative to well-known optical auroras, thus melding the new X-ray results with knowledge of optical auroras.