Caveats Regarding CIAO and Archive Data
Aspect offset of 0.4 arcsec in early 2007
ApplicabilityChandra observations taken after 2006-Dec-10 and processed on or before 2007-May-14.
IssueThese observations are subject to a systematic aspect offset of approximately 0.4 arcsec. This is believed to be the result of a changed thermal environment following the procedure to cool the ACA CCD from -15C to -19C that took place between late Nov-2006 and early Jan-2007. New calibration files to correct this offset were installed effective 2007-May-14 and affected observations were reprocessed to remove the offset.
ResolutionIf the processing date in data files for applicable observations is before 2007-May-14 then observers should retrieve the latest files from the Chandra archive. These will have the current aspect calibration applied.
Observations affected by temporal aspect drift
ApplicabilityObservations affected by temporal aspect drift
IssueUnder some circumstances the positions of X-ray sources can appear to drift by 0.1 to 0.4 arcsec during an observation. This occurs due to thermal alignment changes in the fiducial transfer system periscope related to overall spacecraft heating.
ResolutionContact the CXC Helpdesk for information on improving the aspect image reconstruction for an observation affected by this issue.
Last modified: 06/29/11