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Residual Pointing Uncertainty of 5 arcsec and Combined Images
(Fixed in current pipeline December 2005)
The attitude information reported by the spacecraft (instantaneous RA, Dec and Roll) can be
incorrect by up to 5 arcseconds. Earlier versions of the pipeline did not
perform a fine aspect correction to remove this uncertainty.
This means that when images from multiple pointings were
combined, the sources do not fall exactly on top of each other in the combined image.
The current Swift processing pipeline performs automatic UVOT aspect correction.
However data from earlier versions of the pipeline will still show the effects
of the pointing uncertainty. Until the data has been reprocessed,
users can do their own aspect correction with tools provided as part of the Swift
software package in Ximage. See our UVOT Aspect Correction Analysis Thread for a recipe on using
Swift software to apply aspect correction to UVOT data.
Automatic aspect correction
was added to the UVOT processing pipeline in the SDC in December 2005.
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