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XMM­Newton CCF Release Note
XMM­CCF­REL­0099
EPIC PN Astrometry
Bruno Altieri
December 11, 2001
1 CCF components
Name of CCF VALDATE List of Blocks
changed
CAL VERSION XSCS flag
XMM BORESIGHT 0016.CCF 2000­01­01T00:00:00 NO
2 Changes
Based on a statistical analysis of correlations of pn sources with with USNO stars in the field­of­view
of 349 pointings, a residual of 0.3 degree in pn was found, by J. Tedds and M.Watson (SSC).
Reference : Aboslute astrometry of XMM­Newton fields: eposcorr results, SSC­LUX­
TN­0060 Techincal Note , issue 1.0, Date: 13 Nov. 2001 that can be found at : http://xmmssc­
www.star.le.ac.uk/pages/pubdoc.shtml
This was translated into a correction 0.3 degree of the EULER PSI rotation angle in the 3­2­1
rotation boresight matrix, which describes the misalignement of the respective instruments with
respect to the satellite coordinate frame. The PN EULER PSI angle has therefore been updated
from ­5.4326213896274678E­04 to 4.692730000000000E­03 radian.
3 Scientific Impact of this Update
This new CCF shall bring a better accuracy for PN images, correcting the pn source positions up
to 3­4 arcsec in the towards the very edge of the field­of­view (but much less towards the centre).
1

XMM­Newton CCF Release XMM­CCF­REL­0099 Page: 2
4 Estimated Scientific Quality
With this new BORESIGHT CCF the sky positions of XMM sources are believed to be consistent
between the 3 EPIC cameras to better than 1­2 arcsec across the whole field­of­view, without
applying any additional shift.
This doesn't prevent that a global shift ­ but no field rotation ­ of the MOS and PN images be
applied, to get absolute astrometry via correlations with external catalogues.
Note that the amplitude of this shift can be up to 4 arcsec but with a r.m.s. of the fluctuations
of only 2 arcsec (again see SSC­LUX­TN­0060 for more details). It is believed to be due either to
a limited accuracy of the reconstructed attitude as provided by the star tracker (e.g. dependence
on the position of the guide star in the STR CCD because of field­of view distorsion that could be
corrected in principle in the future) or by thermal deformations between the telescope tube and the
star tracker.
5 Expected Updates
6 Acknowledgements
Jonathan Tedds and Mike Watson for their extremely useful work on EPIC astrometry.