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XMM-Newton CCF Release Note
XMM-CCF-REL-184
EPIC MOS response
Steve Sembay, R.D. Saxton
10 December 2004
1 CCF components
Name of CCF VALDATE EVALDATE Blocks changed XSCS ag
EMOS1 REDIST 0043.CCF 1999-12-10 2000-07-15 CCD REDISTRIBUTION-n NO
EMOS1 REDIST 0044.CCF 2000-07-15 2000-11-09 CCD REDISTRIBUTION-n NO
EMOS1 REDIST 0045.CCF 2000-11-09 2001-04-18 CCD REDISTRIBUTION-n NO
EMOS1 REDIST 0046.CCF 2001-04-18 2001-08-18 CCD REDISTRIBUTION-n NO
EMOS1 REDIST 0047.CCF 2001-08-18 2001-09-26 CCD REDISTRIBUTION-n NO
EMOS1 REDIST 0048.CCF 2001-09-26 2001-11-25 CCD REDISTRIBUTION-n NO
EMOS1 REDIST 0049.CCF 2001-11-25 2002-05-01 CCD REDISTRIBUTION-n NO
EMOS1 REDIST 0050.CCF 2002-05-01 2002-11-07 CCD REDISTRIBUTION-n NO
EMOS1 REDIST 0051.CCF 2002-11-07 - CCD REDISTRIBUTION-n NO
EMOS2 REDIST 0043.CCF 1999-12-10 2000-07-15 CCD REDISTRIBUTION-n NO
EMOS2 REDIST 0044.CCF 2000-07-15 2000-11-09 CCD REDISTRIBUTION-n NO
EMOS2 REDIST 0045.CCF 2000-11-09 2001-04-18 CCD REDISTRIBUTION-n NO
EMOS2 REDIST 0046.CCF 2001-04-18 2001-08-18 CCD REDISTRIBUTION-n NO
EMOS2 REDIST 0047.CCF 2001-08-18 2001-09-26 CCD REDISTRIBUTION-n NO
EMOS2 REDIST 0048.CCF 2001-09-26 2001-11-25 CCD REDISTRIBUTION-n NO
EMOS2 REDIST 0049.CCF 2001-11-25 2002-05-01 CCD REDISTRIBUTION-n NO
EMOS2 REDIST 0050.CCF 2002-05-01 2002-11-07 CCD REDISTRIBUTION-n NO
EMOS2 REDIST 0051.CCF 2002-11-07 - CCD REDISTRIBUTION-n NO
2 Changes
The last release of EPIC-MOS current calibration les (CCFs) which describe the redis-
tribution function of the MOS detectors, i.e.,
EMOS1_REDIST_0035.CCF up to EMOS1_REDIST_0042.CCF and
EMOS2_REDIST_0035.CCF up to EMOS2_REDIST_0042.CCF
made public on 25/08/2004, contains errors. Response matrices (rmfs) for MOS timing
mode spectra, generated by rmfgen using these parameter les, are highly inaccurate.
MOS imaging mode rmfs contain a much smaller error.
1

Corrected canned timing and imaging response matrices were made available on the XMM
SOC website on 15/10/2004. This release contains a new set of CCFs which enable rmfgen
to generate the correct rmfs. The problems with the CCFs 0035 to 0042 are detailed below.
TIMING MODE
Figure 1 shows an example of the old and corrected timing mode rmf for an input energy
of 1 keV. The old rmf peaks at the wrong energy and has the wrong shape and would
produce large errors if used for spectral analysis.
IMAGING MODE
Figure 2 shows an example of the old and corrected imaging mode rmf for an input energy
of 1 keV. The problem here was a mis-setting of the level of the redistribution "shelf".
This shelf is created by photons interacting near the inactive/active layer between the
surface silicon-dixode electrode structure and the active silicon region below. Events can
lose up to 100% of their energy here. This is modelled by a shelf which at 1 keV contains
about 1% of the area under the normalised rmf. The shelf parameter was inadvertantly set
a factor of ten too low. In practice, spectral tting of low-absorption continuum sources
would not be seriously aected by this error as the area under the shelf is relatively low.
It is noticeable in high absorption sources if the user plots his spectra below the energy
at which the absorbing column would be expected to block all of the source ux.
In addition to the functional changes an extra epoch, from 01/05/2002 to 07/11/2002,
has been introduced for both cameras.
3 Scientic Impact of this Update
Figure 3 shows a MOS1 spectral t to the galactic source, 1E 2259+586. This source
has an apparent column of around 9:0 10 21 cm 2 . The underprediction of the shelf
in the old rmf is apparent, although the returned column densities in a simple absorbed
thermal model are 8:84 10 21 cm 2 and 9:04 10 21 cm 2 for the old and corrected rmfs
respectively, i.e. a dierence of about 2%.
Figures 4 and 5 show spectral ts with the corrected rmfs to the MOS1 and MOS2 spectra
of PKS 0745-19 and again 1E 2259+586. In the latter observation MOS2 was in full frame
mode and as the source was piled-up, a larger region of the core was extracted. Hence
the apparent dierence in source count rate between MOS1 and MOS2 in Figure 5. In
both observations the same model parameters were t to both MOS1 and MOS2.
PKS 0745-19, an extragalactic source, has a lower apparent column of around 5:0 10 21
cm 2 . The larger dierence between MOS1 and MOS2 in the predicted shelf levels in
1E 2259+586 may indicate that a further renement is required in either the energy
dependence or the epoch dependance of the level of the shelf. Calibration of this and
other epoch-dependent eects within the rmf is an ongoing process.
2

Figure 1: A comparison of the response functions for a 1 keV narrow line observed in Timing mode using
the old (EMOS1 REDIST 0035.CCF; black) and new (EMOS1 REDIST 0043.CCF; red) CCFs.
4 Estimated Scientic Quality
This update restores the redistribution to that intended with the previous release [1].
Derived columns should be accurate to a few times 10 19 cm 2
5 Expected Updates
The calibration of the MOS redistribution function is an ongoing process and further
updates are likely.
6 Test procedures and results
The new CCF les were used to produce redistribution matrices using rmfgen for imaging
and timing mode and several dierent epochs. These were compared with canned matrices
produced by the MOS instrument team and were seen to be nearly identical in all cases.
References
[1] Saxton, R.D. & Sembay, S. 2004, XMM-SOC-CAL-SRN-0169.
3

Figure 2: A comparison of the response functions for a 1 keV narrow line observed in Imaging mode
using the old (EMOS1 REDIST 0035.CCF; black) and new (EMOS1 REDIST 0043.CCF; red) CCFs.
4

Figure 3: A t to the strongly absorbed MOS-1 (Full Frame mode) spectrum of 1E 2259+586 using the
old (EMOS1 REDIST 0035.CCF; black) and new (EMOS1 REDIST 0043.CCF; red) CCFs.
5

Figure 4: A combined MOS-1 and MOS-2 spectral t (both cameras in Full Frame mode) to PKS 0745-19
using the new redistribution function
.
6

Figure 5: A combined MOS-1 (small window mode) and MOS-2 (Full Frame mode) spectral t to
1E 2259+586 using the new redistribution function
.
7