THE POLAR IONOSPHERIC X-RAY-IMAGING EXPERIMENT (PIXIE)

The Polar Ionospheric X-ray Imaging Experiment (PIXIE) is an X-ray mul tiple-pinhole camera designed to image simultaneously an entire aurora l region from high altitudes. It will be mounted on the despun platfor m of the POLAR spacecraft and will measure the spatial distribution an d temporal variation of auroral X-ray emissions in the 2 to 60 keV ene rgy range on the day side of the Earth as well as the night. PIXIE con sists of two pinhole cameras integrated into one assembly, each equipp ed with an adjustable aperture plate that allows an optimum number of nonoverlapping images to be formed in the detector plane at each phase of the satellite's eccentric orbit. The aperture plates also allow th e pinhole size to be adjusted so that the experimenter can trade off s patial resolution against instrument sensitivity. In the principal mod e of operation, one aperture plate will be positioned for high spatial resolution and the other for high sensitivity. The detectors consist of four stacked multiwire position-sensitive proportional counters, tw o in each of two separate gas chambers. The front chamber operates in the 2-12 keV energy range and the rear chamber in the 10-60 keV range. All of the energy and position information for each telemetered X-ray event is available on the ground. This enables the experimenter to ad just the exposure time post facto so that energy spectra of each X-ray emitting region can be independently accumulated. From these data PIX IE will provide, for the first time, global images of precipitated ene rgetic electron spectra, energy inputs, ionospheric electron densities , and upper atmospheric conductivities.