How good are the relative positions?
On-axis the relative positions appear to be quite good. There is a definite problem with strong sources in the outer part of the PSPC. The quoted errors decrease in value with increasing count rate, reaching rather absurd levels of a few arc sec. Comparison with known identifications often shows a more reasonable 1 arcmin error at the probable 90 percent level. (This comment originates with E. Feigelson.) Also see question #1.
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