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J. Li, J.H. Kastner (Chester F. Carlson Center for Imaging Science, Rochester Institute of Technology), N.S. Schulz, H.L. Marshall (Center for Space Research, Massachusetts Institute of Technology)
Direct measurement of the charge cloud sizes and shapes generated by X-ray photons in charge-coupled devices (CCDs) shows that the typical cloud size is about 1 micron (e.g., Tsunemi et al. 1999, Nucl. Instr. Method A, 436, 32). This means the landing positions of photons that generate split events are near pixel boundaries, not at the pixel centers. The pixel size of Chandra CCDs is 24 microns, so algorithms designed to refine the positions of split events should significantly improve the spatial resolution of Chandra CCD (ACIS) imaging (e.g., Tsunemi et al., 2001, AJ, 554, 496). We are using archival Chandra/ACIS data obtained for the Orion Nebula Cluster (ONC) to evaluate subpixel event repositioning algorithms. We analyze the improvement in image FWHM for ONC sources as a function of total source counts, off-axis angle, and split event percentage, so as to establish the degree of image improvement achieved by (as well as limitations on the success of) subpixel event repositioning. We also present results of subpixel repositioning algorithms as applied to extended sources, such as the compact planetary nebula BD +30 3639 and the X-ray jet from the quasar 3C 273.
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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.