[vsnet-grb-info 3927] Swift XRT boresight update
GCN Circulars
gcncirc at capella.gsfc.nasa.gov
Thu Oct 26 01:22:45 JST 2006
TITLE: GCN CIRCULAR
NUMBER: 5750
SUBJECT: Swift XRT boresight update
DATE: 06/10/25 16:22:39 GMT
FROM: David Burrows at PSU/Swift <dxb15 at psu.edu>
D. N. Burrows (PSU), A. Moretti (INAF-OAB), M. Perri (ASDC), M.
Capalbi (ASDC), L. Angelini (NASA/GSFC) and J. E. Hill (USRA) report
on behalf of the XRT instrument team:
Approximately one month ago the XRT team reported a change in the XRT
boresight since about 1 May 2006 that resulted in decreased
positional accuracy (Burrows et al., GCN Circ. 5628). We have now
completed preliminary analysis of the XRT pointing accuracy over the
mission life and have derived a new boresight appropriate to current
conditions. The XRT team will immediately begin reporting refined
positions based on ground-processed data using the new boresight, as
part of our beta-testing process. This will return XRT refined
position accuracy to its previous level (typically 3.5 - 4
arcseconds, 90% radius.) Note that on-board positions have not yet
been corrected to the new boresight. We will notify the community
when this is done, but for the time being, on-board positions are
several arcseconds away from the actual location, and the error
circle included in automated XRT Position Notices should be increased
by about 50% to account for this systematic error. The new boresight
information will be included in an updated set of TELDEF files
covering different time periods (part of the Swift CALDB), which will
be made available to the rest of the community as part of the next
software release, currently scheduled for no earlier than 27 November, 2006.
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