TECHNIQUES FOR REMOVING NONUNIFORM BACKGROUND IN CODED-APERTURE IMAGING ON THE ENERGETIC X-RAY-IMAGING TELESCOPE EXPERIMENT

The coded-aperture technique for reconstructing images for a position-sensitive detector looking through a stationary URA mask requires that the background illumination be distributed uniformly across the surface of the detector. Non-uniformities in the background are typical of balloon and space-borne detectors, and introduce large artifacts into the reconstructed image, with a subsequent loss of signal-to-noise. Here we describe a technique, employed for the Energetic X-ray Imaging Telescope Experiment (EXITE) to remove the systematic effects of non-uniform background. We explore the time dependence of intensity and two-dimensional shape of the background detector image during the flight. We construct a "flat field" image from observations where x-ray sources were absent from the field of view. We demonstrate that this technique can successfully reduce RMS fluctuations to within a few percent of ideal Poisson statistics.