We have developed a method of improving the spatial quality of ROSAT
HRI data which suffer from two sorts of aspect problems. This
approach requires the presence of a source near the
field
center which has a count rate of 0.1
counts/s or greater.
Although the method does not fix all bad aspect problems, it produces
marked improvements in many cases.
Note added in proof: The "displaced OBI" example of 3C 120 appears to be caused by a bad boresight file since a recent reprocessed image does not have this problem. However, the original data still serve as a valid example.
AcknowledgementsWe thank M. Hardcastle (Bristol) for testing early versions of the software and for suggesting useful improvements. J. Morse contributed helpful comments on the manuscript. The 3C 120 data were kindly provided by DEH, A. Sadun, M. Vestergaard, and J. Hjorth (a paper is in preparation). The other data were taken from the ROSAT archives. The work at SAO was supported by NASA contract NAS5-30934.
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