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XMM­Newton CCF Release Note
XMM­CCF­REL­277
2­D PSF spoke parameterization
A. M. Read & R. Saxton
December 1, 2011
1 CCF components
Name of CCF VALDATE List of Blocks changed Change in CAL HB
XRT1 XPSF 0013.CCF 2000­01­01 ELLBETA PARAMS YES
XRT2 XPSF 0013.CCF 2000­01­01 ELLBETA PARAMS YES
XRT3 XPSF 0013.CCF 2000­01­01 ELLBETA PARAMS YES
2 Change
The elliptical beta, 2­D PSF model (ELLBETA) consists of an elliptical King function plus a central
narrow Gaussian to model the core plus spoke structures (see [1] and CAL­SRN­0263 for a fuller
description). The spoke structure has been reworked in this release to vary the intensity along the
spokes such that
1. The spokes start at a radius, RTHRESH=4.4''. For smaller radii the spoke strength is zero.
2. The spoke strength increases linearly until reaching a peak at RLO=44''.
3. It then decreases linearly until attaining zero intensity at RHI=159.5''. The spoke strength is
zero beyond this radius.
These values are stored as keywords in the header of the ELLBETA PARAMS extension. In
addition some, previously hardcoded, values have been written as keywords into the same extension,
to allow possible future changes to be made within the CCF. The full list of added keywords is:
. RTHRESH ­ minimum radius to start azimuthal filtering (arcsec)
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XMM­Newton CCF Release XMM­CCF­REL­277 Page: 2
. RLO ­ radius at which the spoking peaks (arcsec)
. RHI ­ radius at which the spoking tails to zero (arcsec)
. NSP ­ number of spokes = 16
. CHNGFRAC ­ fraction of image to be filtered (0[none]­1[all]) which defines the strength of
the spoke = 0.375
. SECFRAC ­ strength of secondary spokes = 0.035
. OPHI ­ origin (o#set) angle of primary spoke (degrees) = 11.25
. U ­ azimuthal spoke filtering shape parameter = 0.165
. V ­ azimuthal spoke filtering shape parameter = 0.165
. M1FRAC ­ strength of MOS1 pentangle shape = 0.13
. M2FRAC ­ strength of MOS2 triangle shape = 0.45
For a full description of these parameters, see [1].
Note that the keywords related to the spoke structure currently have the same values for the
three cameras.
3 Scientific impact of this update
This change has been produced in response to a technical note [2] where the fidelity of the ELLBETA
PSF image was investigated by comparing it with a number of very bright piled­up sources. The
spoke structure, as represented in XRTn XPSF 0012.CCF, was found to be too strong. In this
release the spoke intensity, controlled by the parameter CHNGFRAC, has been reduced and made
radially­dependent. This matches better with real sources and hence leads to a reduction in the
number of spurious detections which are found in the wings of bright point sources during source
detection runs.
4 Estimated scientific quality
An analysis of the quality of this CCF has been presented in [3]. The conclusions are that the
on­spoke/o#­spoke ratio now gives a much improved fit to real data.
Nevertheless, in this reanalysis, it was found that one of the sources used for the comparison had
an X­ray scattering halo which biased the final results. A further tuning of the spoking parameters
will be necessary in a future CCF release to account for this.

XMM­Newton CCF Release XMM­CCF­REL­277 Page: 3
5 Test procedure and results
The new CCFs have been used within calview, psfgen and eregionanalyse to test that they
produce the correct PSF images and encircled energy values.
The modified SAS code needed to take advantage of the new CCF structure is not yet public.
To ensure that these changes do not adversely a#ect the current public SAS (v11.0) the same three
tasks, calview, psfgen and eregionanalyse were executed from the current SAS using the new
CCF elements. No problems were seen.
6 References
[1] Read, A., Rosen, S., Saxton, R. & Ramirez, J. 2011, A&A, 534, 34
[2] Owen, R. & Ballet, J. 2011, SSC­CEA­TN­1001, v1.1.
[3] Owen, R. & Ballet, J. 2011, SSC­CEA­TN­1001, v2.1. (http://xmm2.esac.esa.int/documents/CAL­
SSC­CEA­TN­1001­2.1.ps.gz)