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XMM-Newton CCF Release Note
XMM-CCF-REL-218
RGS Cool Pixels
C. Gabriel
June 29, 2006
1 CCF components
Name of CCF VALDATE EVALDATE Blocks changed XSCS ag
RGS1 COOLPIX 0001 2000-01-01T00:00:00 COOLPIX NO
RGS2 COOLPIX 0001 2000-01-01T00:00:00 COOLPIX NO
2 Changes
This is the rst release of a new calibration le for making possible the removal of columns char-
acterized by an anomalous large charge transfer ineфciency in the RGS chips. The eects of these
anomalous columns are not easily seen and are only perceptible by a combination of large amounts
of data and enough signal on the chip. Fig. 1 shows the eects both in space and energy plots on
one of the aected columns, probably caused by charge traps in the column producing large CTI.
The normal energy region selection, necessary for discrimination of the spectral orders, discards
consequently a large part of the signal. Removal of such suspicious "cool" columns should clearly
improve the quality of the spectrum.
Derivation of the "cool" columns set was performed by the RGS instrument group at SRON
using all the Mkn421 data observed in the rst 5 years of operations. The numbers of aected
columns by the RGS1 and RGS2 instruments are 55 and 32, respectively.
A new function accessing these calibration data has been put in place, which is called from the
SAS task rgsenergy, if the parameter "keepcool" is disabled (eg. set to "NO"). The agged columns
are then added to the agged bad pixels and bad columns and handled in the same way. These
changes are going to be eective with the release of SAS 7.0.
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3 Scientic Impact of this Update
A general improvement in the spectral tting quality can be expected, especially for the analysis of
small wavelength scale eects. This could be checked using the RGS rst order spectra from the
Mkn421 observation 0099280201, taken in revolution 165. Using a simple absorbed power law model
ts were conducted with and without agging the cool columns. In the latter case the chisquare
was reduced from 1.34/DoF to 1.11/DoF.
4 Estimated Scientic Quality
The inclusion of "cool" columns should improve the quality of spectral tting, since the eective
area for the channels containing them will be properly calculated. These channels appeared so far
very often as outliers in the tted signal distributions, if a signicant signal was expected.
Please take into account that:
 the "cool" columns were to a certain percentage recognized as "low count" columns in the past
and have been consequently agged as bad columns for certain periods of the XMM mission.
So the total number of 87 columns which can be agged through the inclusion of these new
CCFs is an upper limit, and the number of agged columns in addition to the defaults depends
on the epoch of the observation,
 this new correction should be applied mainly for the study of small wavelength eects and it
is therefore not implemented as a default choice,
 at the moment the SAS implementation does not allow the user to separate "cool columns" and
"bad columns" for further quality selection, eg. the "NEXT to BADPIX" agging (which is
the default) applies to both types in the same way. Further studies should show if disentangling
them is advisable.
5 Expected Updates
The evolution of "cool" columns should be monitored for establishment of periods of validity. This
is considered diфcult, however, due to the large amounts of data necessary to this purpose.
6 Test procedures
General checks:

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 use FV (or another ts viewer) for le inspection. It should contain 1 binary extensions
(COOLPIX)
 use the upgraded SAS (incl. rgsbadpix 2.18.2) for validating ingestion and use of the cool
columns information. Compare results with parameter keepcool="yes" and ="no").
7 Summary of the test results
The ts viewer fv was used to inspect the 2 CCF les, wrt their structure, validity dates and contents
of the extension. Everything OK.
rgsproc has been ran with and without the new correction on a Mkn421 dataset. Improvement
of the spectral tting was achieved, the columns were correctly agged.

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Figure 1: Spatial and energy plots detail, showing an aected column by large CTI