Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://xmm.vilspa.esa.es/docs/documents/CAL-TN-0018-2-2.pdf Äàòà èçìåíåíèÿ: Mon Jul 12 13:27:12 2004 Äàòà èíäåêñèðîâàíèÿ: Mon Oct 1 20:59:16 2012 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: annular solar eclipse

XMM-EPIC status of calibration and data analysis XMM-SOC-CAL-TN-0018 Page: Issue: M. Ki Date: -1­ 2.2 rsch 29.06.04

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EPIC status of calibration and data analysis
Marcus Kirsch with the inputs from the whole EPIC Consortium please send all comments to mkirsch@xmm.vilspa.esa.es

This document reflects the status of the calibration of the EPIC camera as implemented in SAS 6.0 with all available CCFs at 30/06/2004. Furthermore the outlook is considered for improvements of calibration which at the moment can be expected for the next SAS release.

Contents:
1 Calibration Overview _________________________________________________________ 2 1.0 Summary ______________________________________________________________ 2 1.1 Imaging _______________________________________________________________ 4 1.1.1 Astrometry _________________________________________________________ 4 1.1.2 Point Spread Function and Encircled Energy _______________________________ 5 1.2 1 1 1 1 .2 .2 .2 .2 Effective Area ____________ .1 Mirror collecting area ___ .2 Filter transmission _____ .3 CCD Quantum efficiency .4 Vignetting ____________ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 1 1 9 9 9 0 1

1.3 Energy Redistribution __________________________________________________ 13 1.3.1 MOS _____________________________________________________________ 13 1.3.2 PN _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 1 3 1.4 1.5 1.6 CTI/Gain _____________________________________________________________ 14 Background ___________________________________________________________ 15 Timing _______________________________________________________________ 16

1.7 Examples of EPIC spectra _______________________________________________ 18 1.7.1 PKS 0558-508 _____________________________________________________ 18 1.7.2 PKS 2155-304 _____________________________________________________ 19 1.8 2 2.1 2 2 2 2 Cross Calibration with RGS and other Satellites ____________________________ 20 New features in .1 SAS 5.3.0 _ .2 SAS 5.3.3 _ .3 SAS 5.4.1 _ .4 SAS 6.0.0 _ SA S ____ ____ ____ ____ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 2 2 2 2 2 0 0 0 0 1 Data Analysis ______________________________________________________________ 20 .1 .1 .1 .1

2.2 Data Analysis _________________________________________________________ 21 2.2.1 MOS _____________________________________________________________ 21 2.2.2 PN _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 2 2


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1

Calibration Overview

This section gives a short overview of the status of the calibration of the EPIC instruments MOS1, MOS2 and PN, operating on-board the XMM-Newton observatory. It summarises the quality of the calibration to the extent that this may influence the scientific interpretation of the results. The instrument calibration is based on a physical model of the various components including mirror response, filter transmission and detector response (energy redistribution, gain, CTI). During ground calibration various components were calibrated and the physical model for each component was optimised. These models were verified in flight and are, where relevant, continuously monitored (e.g. contamination of the detector, changes in gain and CTI due to radiation damage). Where applicable, corrections which are needed for these time-variable changes will be applied to the Current Calibration Files (CCFs) and/or the processing software. For more detailed information see the release notes of the CCFs at: http://xmm.vilspa.esa.es/ccf/releasenotes/ Blue coloured text gives distilled information or html links. Red coloured text marks current problems.

1.0

Summary

We give in the next table a summary of the status of the calibration:

Effect Absolute Astrometr y Relative Astr. within 1 camera Relative Astr. between 2 cameras Point Spread Function Relative Effective Area Absolute Effective Area Absolute Energy scale Relative Timing Absolute Timing

Max. Error 1''(r.m.s.) 1.5''(r.m.s) 1.5''(r.m.s) 2% 5% 10 % 10 eV P/P<1E-8 250-500 µs

Energy dependent NO NO NO YES YES YES YES NO NO

Off axis angle dependent YES YES YES YES YES YES YES NO NO

Improvements since the last issue of that document: · Vignetting and Boresight: One of the most important outstanding problems of the calibration is a possible offset of around 1' in the telescope axis from nominal. This does not affect the astrometry but could be the reason for flux discrepancies between MOS and PN caused b y the vignetting correction which has not yet been adapted to this offset. The offset was determined and implemented in the corresponding CCF (XMM_MISCDATA_0020). The new consideration of the right optical axis position improves the vignetting correction, such that it is now applied for correct off axis angles, that could not be calculated correctly before due to the wrong information for the optical axis. This improves differences in flux for off axis sources for each camera from ±14 % to ± 5 %. Detailed information at: (see: XMM-SOC-CAL-SRN-156). The new optical axis position required also a new XMM_BORESIGHT CCF which holds for each instrument a triple of three angles describing the alignment of the respective instrument boresight with respect to the satellite coordinate frame. Using the OMC2/3 field new boresight alignment angles for all the three cameras have been calculated.


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In a further analysis the XMM_BORESIGHT CCF in combination with the MOS LINCORD CCFs has been refined in order to improve the astrometry. (see XMM-SOC-CAL-SRN-168 and XMM-SOC-CAL-SRN-166) · PSF: New analysis has refined the values stored in the King function parameterisation of the 3 EPIC telescope point spread functions (PSFs), i.e. XRT1, XRT2 and XRT3. They are stored in the KING_PARAMS extension of the CCF, and are tabulated as functions of ENERGY and THETA (off-axis angle). The linear dependencies of the PSF core radius r0 and slope with energ y, obtained through earlier studies, have been found to be incorrect; in actuality, the r0 and curves are seen to be initially much flatter with energy, at least out to ~ 8-10 keV, where they then become rapidly steeper. Usage of the new PSFs yields consistent spectral fits for various different annular extraction regions such as they are used in the analysis of piled-up sources. A consequence of improvements to the model of the PSF is that, in the case of piled-up point sources, excising the piled-up core is now considered to be a valid analytical strategy. Users should use the epatplot SAS package to assess the presence and level of pile-up (see: XMM-SOC-CAL-SRN-0167). MOS Low Energy: Observations of calibration targets confirm a significant change in the low energy redistribution characteristics of the MOS cameras with time. This change is probably due to an increase in the surface charge loss property of the CCDs which degrades the low energ y resolution. Epoch dependant calibration files have been produced which reflect these changes, but users should be aware that uncertainties in the model of the redistribution function of the MOS cameras remain. Spectral fitting can be performed down to 150 eV, but in these cases it is recommended that a systematic error of 2 % be applied. (see: XMM-SOC-CALSRN-169). MOS Gain: An improvement in the epoch dependent CTI and Gain correction in SAS 6.0.0 has reduced the uncertainty in the energy calibration from 10 to 5 eV for the imaging modes of the MOS cameras. (see: XMMSOC-CAL-SRN-161). MOS CTI: For MOS-Timing mode the CTI correction was changed improving earlier over correction by debugging some erroneous code in SAS. MOS Timing mode energ y accuracy does now agree with the imaging modes within 0.3 %. (source code change in SAS 6.0).

·

·

·

Important ongoing calibration topics: · PN CTI: The EPIC pn Small Window mode currently shows a Gain/CTI under correction of ~2-3 % most prominent around the O-edge. This can lead to residuals in the fitted spectra of up to 20 %. A better CTI correction will be provided as soon as possible with a new CTI CCF release. The internal calibration source shows an over correction of up to 15 eV at Mn-K in pn Extended Full Frame mode, that is related to imperfect Gain/CTI correction. This is currently under investigation with special calibration observations. PN redistribution: o EPIC-pn spectra from zeta Puppis have shown that the spectral response below about 400 eV might not yet be correctly reproduced. In particular the re-distribution as modelled in SAS 6.0.0 might be higher than seen in the data. This can lead to large (30%) systematic errors in the absolute flux of very soft spectral components (kT<100 eV). Further observations with different read-out modes are planned to investigate the problem. EPIC-pn spectra show an excess below 500-1000 eV of about 20 % in SW mode. Current investigations point in the direction of a redistribution problem above the O-edge. On-going work on the pn redistribution is expected to bring down the discrepancy below 10%.

·

o

· ·

EPIC-MOS cameras show for energies above 3keV an excess up to 15 % with respect to EPIC-pn that might be related to various system components and is under investigation. PSF core: The improved King function of the PSF is a good but not perfect fit to the PSF of the the core of the PSF is very slightly underestimated. This effects the MOS more than the pn (as the pixels are much smaller than the pn pixels). This can produce an error in the enclosed energy of depending on instrument, energy and extraction radius. Work is currently underway to model combination of a King function plus a Gaussian function (the latter to model the slight excess at th telescopes, as MOS detector at most ~2 %, the PSF as a e core).

·

Astrometry: investigation. This could lead to an uncertainty of up to 1.5'' at the edge of the XMM-Newton field of view.


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1.1

Imaging

1.1.1 Astrometry Astrometry means: The precision with which astronomical coordinates can be assigned to source images in the EPIC focal plane. We distinguish between: Absolute Astrometry (relative to optical coordinates, without taking into account possible shifts due to spacecraft miss-pointing), Relative Astrometry per camera (within one camera after applying possible shifts due to spacecraft miss-pointing) and Relative Astrometry between cameras (positions in one camera relative to an other one) The XMM-Newton absolute astrometry accuracy is limited by the precision of the Attitude Measurement System. Fig. 1-1 shows that the shift from the XMMNewton-EPIC to the optical frame is on average 0'' with a standard deviation of less than 0.8'' per axis. Hence the Absolute Pointing Accuracy is considered to be better than 1" (r.m.s.). The relative astrometry within each camera is accurate to 1.5" for all cameras and over the full field of view. The MOS metrology has been revised with SAS6.0, searching for systematics in the offsets of MOS peripherical CCDs with respect to the central CCD by using observations on rich stellar fields. CCD offsets of up to 2.7" have been corrected in the MOS LINCORD CCF issue 17. With this new CCF the MOS relative astrometry accuracy has been assessed to be 1.5" (r.m.s.) while it is as good as ~1.0" (r.m.s.) for EPIC-pn. Among all three EPIC cameras the relative astrometry is also estimated to be better than 1.5" across the whole field of view. Note that for faint MOS sources the detection limit the statis accuracy of the measurement li the 90 % confidence contours t 4". near tical mits o 2i on der an t he

Figure 1-1: Histogram of the distribution of offsets for each EPIC camera with respect to the 2MASS reference frame projected on to the two spacecraft axis. Top: MOS1, Middle: MOS2, Lower: pn (Details at XMM-SOC-CAL-SRN-168)

A possible residual in the posit angle rotation order of 0.1 deg is un investigation. This could lead to uncertainty of up to 1.5'' at XMM-Newton field of view.


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1.1.2 Point Spread Function and Encircled Energy Point Spread Function: The spatial distribution of light in the focal plane in response to an observed (monochromatic) point source. The PSF integrates to 1 over the infinite focal plane. Encircled Energy: The fraction of the energy of a point source collected within a certain radius. Though the shape of the PSF is quite complex, the radially averaged profile can be adequately represented b y an analytic function - a King function - whose parameters, core radius r0 and index , are themselves functions of energy and offaxis angle:

PSF

=

r A 1 + r 0



2



-

It is worth noting that both this function and its integral are analytic. Earlier work (EPIC-MCT-TN-011, EPIC-MCT-TN-012, XMM-CCF-REL-116) used many bright point and off axis to determine the energ y dependent PSF. This resulted in a linear dependency of r0 and off-axis angle. It is shown in XMM-SOC-CAL-SRN-0167 that this linear dependency is not valid - the r0 and are seen to be flatter (almost constant) with energy (at least out to ~ 8-10 keV). Thereafter t rapidly turn steeper. sources both on with energ y and dependencies of he dependencies

Figure 1-2: Surface brightness radial profiles (crosses) plus fitted King profiles (lines) for two examples: (left) MCG-06-30-15 Rev. 303 pn at 6 keV (right) MCG-06-30-15 Rev. 302 MOS2 at 0.475 keV.

Two threads of analysis using data from very long and clean Small Window mode observations of very bright non piledup sources were followed: One involved the forming of narrow-energy-band images, and fitting the surface brightness radial profiles obtained from these images with a King function to obtain r0 and as a function of energy. A second analysis thread involved the extraction of spectra from narrow annuli around point sources, and once ARF files had been


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generated (this involving the actual form of the PSF), the spectra were fitted with standard spectral models, to see how (if at all) the spectral parameters obtained varied with extraction radius. This whole process was repeated for several sets of PSF parameters (including those obtained from the surface brightness radial profile fitting described above). Two examples of surface brightness radial profiles plus fitted King profiles are shown in Fig.1-2. The resultant dependencies of r0 and are seen to be flatter (almost ~constant) with energ y, at least up to ~ 8-10 keV (where the r0 and relationships turn over) than in the previous parameterisation of the PSFs as shown in Fig. 1-3. The new PSFs were used in the analysis of spectra extracted from narrow annuli around a number of bright point sources, as described above. Fig. 1-4 shows how the fitted normalization and power-law index vary as a function of the radial distance of the extraction regin (0-5", 5-10" etc.) for the old CCF PSFs and the new CCF PSFs described here, for the MCG-06-30-15 Rev.302 data. A point source, of course, should show no variation in fitted spectral parameter whether the spectrum is extracted from the very centre of the distribution or from the wings, but usage of previous PSFs result in a very wide range in spectral parameters for different radii. Usage of the new PSFs gives rise to a very significantly improved situation, with the fitted normalization and power-law index remaining constant and 'flat ' with radius. Figure 1-3: r0 ­ Energy (top) and ­ Energy (bottom)dependencies for the MOS1, MOS2 and pn on-axis PSFs.

Figure 1-4: Plots showing how the fitted normalization (top) and power-law index (bottom) vary as a function of the radial distance of the extraction region (left to right: 0-5" (circle), 5-10" ( annulus) etc), using the current CCF PSFs (left) and the new CCF PSFs (right) for the MCG-06-30-15 Rev. 302 data.


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A major problem with the previous parameterisation was its inability to produce consistent spectral fits for annular extraction regions such as those for instance used for the analysis of piled-up sources. Hence MCG-6-30-15 (from Rev 302) has been extracted from annuli of 5-40", 10-50" and 15-60" and fits compared to those of a circular extraction (030"). This has been performed using the old and the new PSFs, and the results are presented in Fig. 1-5. Whereas usage of the old PSFs results in a per instrument normalization variation of up to 40%, and changes in the fitted spectral slope of 0.2, the new PSFs give rise to normalization variations of nearer 5% and a spectral slope change of at most 0.03. Note that the King function is a good but not perfect fit to the PSF of the telescopes, as the core of the PSF is very

Figure 1-5: Plots showing how the fitted normalization (top) and power-law index (bottom) vary as a function of extraction region (left to right: 0-30" circle, 5-40" annulus, 10-50" annulus, 15-60" annulus), using the old CCF PSFs (left) and the new CCF PSFs (right) for the MCG-06-30-15 Rev.302 data. slightly underestimated. This effects the MOS more than the pn (as the MOS detector pixels are much smaller than the pn pixels), and can be seen in Fig. 1-2, the MOS PSF (right) fit lying underneath the data points at the very centre. This can produce an error in the enclosed energy of at most ~2 %, depending on instrument, energy and extraction radius. Work is currently underway to model the PSF as a combination of a King function plus a Gaussian function (the latter to model the slight excess at the core).


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Off-axis PSF As yet, no sources bright enough for this new type of analysis to be performed off-axis have been observed. As such, the general off-axis results of previous work (EPIC-MCT-TN-011, EPIC-MCT-TN-012, XMM-CCF-REL-116) have been used to transform the new on-axis parameters presented here to projected off-axis values.

How the PSF varies off-axis is only known reasonably well for small off-axis values. The following two plots show the details for the reliability:

Figure In the green region: For low energies and nearly statistics for these measurements is good. Error evaluations for these curves are not very "far" from

1-6: Reliability for PSF on-axis positions a large quantity of data is available and in general bars are in general small (/r0 (or ) <~ 1 %) and the r0 and the final fit (r/ r < 5% is the worst case).

In the yellow regions: for some off-axis angles few measurements are available (< 2-3) at the different energies. In general these measurements have large errors (/rc0 ~ 10%) and the r0 and parameters for these sources sometimes are "far" from the final best-fit values (r /r can be as large as 10-20%). In the red region: no calibration data are available, and best-fit values coming from the model are an extrapolation, not a real calibration.

Addendum: Off-axis PSF While the EPIC-pn PSF is azimuthally symmetric, the placing of the CCDs in the MOS cameras to follow the focal plane results in a chip-to-chip variation in the MOS PSF (ref Saxton, R.D., Denby, M., Griffiths, R.G., Neumann, D.M., 2003, Astron.Nach., 324, 138.). This is not currently modelled in the SAS calibration but will result in an azimuthal variation in the encircled energy fraction which is dependent on the extraction radius and the off-axis angle. This variation is not yet quantified but is estimated to be ± 4% for a source circle of radius 25" at an off-axis angle of 7'.


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1.2

Effective Area

Effective Area means: the effective collecting area of the optical elements and detector s ystem of the EPIC cameras as a function of energy. For on-axis sources an internal accuracy of better than 5% in the determination of the total effective area is reached over the spectral range from 0.4 - 12 keV for each instrument separately. The cross calibration between MOS1 and MOS2 agrees within 5 %. The MOS/PN cross shows a up to 10 % the PN (see 1.7.2). CCD-Quantum-Effi calibration agrees to 10 % from 0.4 keV to 12 keV. In the range from 0.3-1.0 keV the PN camera higher flux than the MOS, while for energies above 1.5 keV the MOS flux is up to 10 % higher than This is currently under intens investigation and could be due to uncertainties in the vignetting and ciency.

1.2.1 Mirror collecting area Mirror collecting area means: the face-on area of the mirror s ystem that reflects X-rays to the focal region The mirror collecting area has been measured on ground and verified in orbit. 1.2.2 Filter transmission Filter transmission means: the fraction of X-ray photons that through pass the filter The filter transmission has been measured on ground. The following plot shows filter transmission curves for all the cameras. For the thick filter the green curve shows the single transmission function currently used in the CCFs for MOS1, MOS2 and PN. Later the CCFs will be refined to reflect the small differences among the three thick filters.

Figure 1-7: Filter transmissions in CCF and ground calibration filter measurement data points. green - thick, red - medium, blue- thin (Thin1 & Thin2 have the same CCF) ground: squares-PN, star-M1, diamond M2 , CCF: dashed lines


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1.2.3 CCD Quantum efficiency Quantum Efficiency means: the fraction of photons that generate an event in the CCD. Ground calibration measurements have shown that the quantum efficiency of MOS CCDs is spatially uniform above 400 eV. Below this energy spatial variations within a CCD are seen as patches in the outer parts of the CCDs where the response is degraded. This inhomogeneity is currently not taken into account by the SAS.

Figure 1-8:QE ground measurements and CCF (upper MOS1 CCD1, lower PN)


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Figure 1-9: QE spatial inhomogeneities within MOS1 appearing only at very low energies (left 150 eV, right 400 eV). The regularly spaced "hot pixels" seen in the 400 eV image are not hot pixels at all, they have been interpreted as false events generated by the reset-on-demand mechanism.

1.2.4 Vignetting Vignetting means: reduction in the effective area with radial distance from the telescope's axis. The telescope vignetting is well determined for off-axis angles of up to more than 10'. One of the most important outstanding problems of the calibration was an offset of around 1' in the telescope axis from nominal. This did not affect the astrometry but could have been the reason for some of the flux discrepancies between MOS and PN caused by the vignetting correction which has not yet been adapted to this offset in SAS versions earlier than 6.0.0. The offset was determined and implemented in the corresponding CCF (XMM_MISCDATA_0020). With SAS 6.0.0 and the current available CCF the new consideration of the right optical axis position improves the vignetting correction. However the vignetting correction itself has not changed at all, the only difference is, that it is now applied for correct off axis angles, that could not be calculated correctly before due to the wrong information for the optical axis. This improves differences in flux for off axis sources for each camera from ± 14 % to ± 5 %. Detailed information can be found in XMM-CAL-TN-54 and XMM-CAL-SRN-0156.


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Figure 1-10: Average vignetting measured over 4 azimuths at an off-axis angle of around 10's derived from Calibration measurements of the SNR G21.5-09


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1.3

Energy Redistribution

Energy Redistribution means: The energy profile recorded by the detector system in response to a monochromatic input. 1.3.1 M OS The same energy redistribution matrices can be used for all MOS imaging modes. Since SAS 5.4.1, rmfgen supports all MOS modes and takes the observed change in energy resolution with time into account. Also ready-made redistribution matrices, addressing this, are available at http://xmm.vilspa.esa.es/external/xmm_sw_cal/calib/epic_files.shtml.

Figure 1-11: Energy resolution MOS 1 CCD1 in eV. The drop after rev 532 is caused by the cooling of the cameras

1.3.2 PN The energ y redistribution is mode dependent for the PN camera. That means that different response matrices are needed for the different modes. Since SAS 5.4.1 rmfgen supports all modes. Also read y-made matrices can be used, which can be obtained at: http://xmm.vilspa.esa.es/external/xmm_sw_cal/calib/epic_files.shtml. The response is mainly studied for on-axis sources. The and BURST only the CCD containing the focal point is resolution) is the RAWY dependence (see 2.2.2). Other vignetting is part of the effective areas computed by arfg More information on rmfgen and arfgen are available at: http://xmm.vilspa.esa.es/sas/current/doc/arfgen/index.html http://xmm.vilspa.esa.es/sas/current/doc/rmfgen/index.html. response matrices are for all CCDs (note that for SW, TIMING used); the only dependence of the redistribution (i.e. the energ y off-axis (radial) dependencies do not exist in the re-distribution, en.

We do not see any significant degradation of energy resolution with time in PN. EPIC-pn spectra from Zeta Puppis have shown that the spectral response below about 400 eV is not yet correctly reproduced. In particular the re-distribution as modelled in SAS 6.0.0 is higher than seen in the data. This can lead to large (30%) systematic errors in the absolute flux of very soft spectral components (kT<100 eV). Further observations with different read-out modes are planned to investigate the problem.


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1.4

CTI/Gain

CTI means: Charge Transfer Inefficiency is the imperfect transfer of charge as it is transported through the CCD to the output amplifiers during read-out. Gain means: Gain is the conversion (amplification) of the charge signal deposited by a detected photon, from ADU (Analogue to digital unit) charge into energy (electron-volts). For the instruments in normal conditions, the Gain and CTI are known well enough such that the line energy can be determined with an uncertaint y of 5 eV over the full energy range for all MOS imaging modes and with an uncertainty of 10 eV over the full energ y range for all pn imaging modes except pn Extended Full Frame where for the internal calibration source an over correction of up to 15 eV can be seen. This is currently under investigation with special calibration observations. An improvement in the epoch dependent CTI and Gain correction in SAS 6.0.0 has reduced the uncertainty from 10 to 5 eV for the MOS cameras. Abnormal conditions include the eclipse seasons and solar flares (marked by the vertical lines in figures 1-11, 1-12), where the gain at the beginning of an orbit (i.e. during calibration observations) can vary significantly from the gain for the remainder of the orbit, due to temperature variations in the onboard electronics. No correction has been achieved yet for this, but the effect of the EMAE (EPIC MOS Analogue Electronics) temperature excursions during scientific observations are usually small (MOS1: < 10eV at Mn-K and < 5eV at Al-K).

Figure 1-12: MOS 1 CCD 1 Calibration source line positions at Al-K (upper) Mn-K (lower) The relative accuracy of the Timing modes compared to the imaging modes is better than 0.3 % over the full energy range. For the PN, deviations in the gain occurred during the first eclipse season (revolutions 60-80) and during occasions when the RGS was first turned off to diagnose a CCD chain failure (revolutions 136-146, and 149-150), when the platform temperature changed significantly and 10 - 30 eV discrepancies were occasionally observed. The PN team has established a good correlation to implement a temperature dependent gain correction, which is already implemented in the SAS, but not yet activated, since full consequences of the correction have not yet fully been investigated. The feature however is currently regarded as low priority. Fortunately the temperature excursions are now dramatically reduced. Revolution 60 ­ 80 136-146 149-150 Note: For Problem 1st Eclipse RGS off RGS off

PN a lower temperature means a lower gain (too low energies) while for MOS it is vice versa


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Figure 1-13: Cas-A spectra in different PN-Modes (count rate spectra are scaled for clarity)

1.5
1.

Background
The astrophysical background dominated by thermal emission at lower energies (E<1 keV) and a power law at higher energies (primarily from unresolved cosmological sources). This background varies over the sky at lower energies. Soft proton flares where the spectrum varies from flare to flare. For weak sources the only option is to select quiet time periods from the data stream for analysis. To identify intervals of flaring background the observer should generate a light curve of high energy (E > 10 keV) single pixel (PATTERN = 0) events. To identify good time intervals use the selection criteria: · · MOS: < 0.35 cts/s (#XMMEA_EM && (PI>10000) && (PATTERN==0) on the full FOV PN: < 1.0 cts/s (#XMMEA_EP && (PI>10000) && (PATTERN==0) on the full FOV

There are three different types of background:

2.

Note: These selection criteria assume that sources above 10 keV do not contribute significantly to the overall intensity.


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The high-energ y proton induced background. These events are created directly by the protons penetrating the CCDs and indirectly by the fluorescence of satellite material to which the detectors are exposed. This background is being actively investigated and there are two samples of blank sky high galactic latitude background event files available at http://xmm.vilspa.esa.es/external/xmm_sw_cal/calib/epic_files.shtml for use as templates. The goal is to provide a generic-modelling tool for all observation scenarios.

The following two images show the strong metal line features that make the background subtraction complex, especially for large clusters and radial temperature determination. Explanatory notes for background subtraction are given: http://xmm.vilspa.esa.es/external/xmm_sw_cal/calib/epic_files.shtml.

Figure 1-14: MOS-Al-K at 1.48 keV (left) and PN Cu-K at 8.04 keV (right) internal background caused by X-ray fluorescence lines correlated with the structures of the electronic board (pn-Cu-K) and the more distant camera itself (MOS Al-K)

1.6

Timing

Absolute timing means: Locating events in time with reference to standard time defined by atomic clocks or other satellites. Relative timing means: The capacity to measure time intervals and periodicity reliably The release of SAS 5.3.3 included for the first time all necessary components to support timing analysis with outstanding time resolutions down to 29 and 7 microseconds for PN Timing and Burst modes respectively. Tests on data from the Crab pulsar taken during XMM-Newton's performance verification campaign in early 2000 indicate that the relative deviation in the observed pulse period w.r.t. the most accurate radio data available (P/P) is now considerably less than 10-8, with an absolute timing accuracy of < 500 microseconds. For the Crab pulsar the new results now conform with estimates of the theoretically attainable accuracy with XMMNewton and the expected statistical errors. Further investigations of periodicity of other objects are currently underway. Because of anoth with all the Data to the EPEA that second of OBT), not only with the er improvement in converting the onboard time (running counter, kept by the CDMU and synchronised Handling units. 48 bits, resolution (LSbit) is 1/65536 secs) to the event time (time in a counter internal timestamps each frame. This timer is reset to 0 at the beginning of each observation, at a sharp (integer) the user should make sure that the data are fully reprocessed with the SAS higher than SAS 5.3.3 and new "barycen" task of SAS 5.3.3 in order to achieve the highest timing accuracy.


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Figure 1-15: 2-distribution of epoch folding period search (upper) folded light curve for the Crab


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1.7

Examples of EPIC spectra

This section gives only two examples of spectra, since we will publish in the near future a special document of XMMNewton Cross Calibration, that will in detail elaborate the current status of XMM-Cross-Calibration. 1.7.1 PKS 0558-508 This section presents a comparison of EPIC results for the radio-loud narrow-line Seyfert 1 galax y PKS0558-508. Figure 1-17 shows the simultaneous fits to EPIC data where the only independent parameter was a scale factor between the different instruments. The refined PSF correction brings now a much better agreement for the three cameras for that overall normalization. Whereas in previous versions the EPIC cameras agreed within ± 10-12 % in that overall normalisation we see now more values like ± 5 %. For details see XMM-SOC-CAL-TN-0052 (to be released soon).

Figure 1-16: Simultaneous spectral fits to PKS0558-508. Black: pn, red, MOS1, green: MOS2. The zoomed ratio (lower panel) has been binned more for clarity.


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1.7.2 PKS 2155-304 The following plot shows a simultaneous fits to EPIC PKS2155-304 data where the only independent parameter was a scale factor between the different instruments. Also her the new PSF correction improved the overall normalization from ± 10-12 % to ± 5 %. The larger residuals below 600 eV are due to uncertainties arising from the complicated shape of the redistribution function and the low energy effective area in combination with a gain problem of the pn-SW mode, that is currently under investigation. Above 7 keV the residuals probably arise form uncertainties in the background subtraction method.

Figure 1-17: Simultaneous spectral fits to PKS2155-304. Black: pn, red, MOS1, green: MOS2. The zoomed ratio (lower panel) has been binned more for clarity.


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1.8

Cross Calibration with RGS and other Satellites

These sections have been removed since in the near future a dedicated Cross Calibration Document will be available at the XMM-Newton Science Operations Center web portal.

2

Data Analysis

This section provides an overview of what the SAS is able to do with the V6.0.0 release. Also included is a guideline of how to work with the different modes of the cameras.

2.1
2.1.1 · · · · ·

New features in SAS
SAS 5.3.0 The MOS CTI correction has been improved to take into account the changes which have occurred since launch. A new task, evigweight, assigns a vignetting correction to each individual event. This allows extraction of vignetting-corrected images and spectra directly. A new task, epatplot, is available to identify pile up. The PN background rejection and CTI correction have been significantly improved. The tasks rmfgen and arfgen now reproduce the canned matrices to within 1%. Also, the full range of event patterns is supported. Further, rmfgen supports the major observing modes. SAS 5.3.3 The latest CTI correction for PN SW and LW mode has been implemented. EPIC-PN Timing and Burst mode response files are available SAS 5.4.1 MOS CTI correction has been modified in order to compensate the stepwise degradation after solar flares Degradation of the MOS intrinsic spectral resolution due to the larger noise component of the degraded CTI has been modelled. Refined calculation of the MOS gain as a function of observation epoch has been implemented. epatplot now also indicates the distribution and amount of invalid PN patterns to ease flux comparison in the case of pattern pile-up. New PN quantum efficiency function which is based on measurements of the thickness of the SiO2 layer on top of the CCD.

2.1.2 · · 2.1.3 · · · · ·

Figure 2-1: New (red) and old ( green) PN QE


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Refined spectral redistribution for PN (concerns all readout modes) at energies below 600 eV. The redistribution was adjusted to achieve agreement in column density derived from PN and Chandra LETG spectra of RXJ1856.3-3754. calpnalgo now receives all quantities from CCFs. The SW/LW mode CTI-correction function for PN has been modified. arfgen and rmfgen now support all modes (incl. TI and BU modes). SAS 6.0.0 The new SAS task epreject corrects shifts in the energy scale of specific pixels due to high-energy particles hitting the EPIC PN detector during offset map calculation and suppresses the detector noise at low energies by statistically flagging events based on the known noise properties of the lowest energ y channels. In the case of timing mode data, flagging of soft flare events may be performed. An additional function is added to emevents that performs a blanking of bad-energy columns and handles those now correctly as dead areas. emevents is now doing a filtering & removal of flickering pixels decreasing significantly the noise at lowenergies. The new SAS tasks ebadpixupdate allows operations on bad pixels at the level of the calibrated events list epatplot: The optional input of a background eventset now allows the determination of background-subtracted pattern fractions. This is useful, e.g., in the case of extended source analysis or close to spectral background features. badpixfind: The task now permits bad pixel searching on calibrated multi-chip (i.e. final pipeline product) eventsets. Previous versions only operated on raw event sets.

· · · 2.1.4 ·

· · · ·

·

2.2

Data Analysis

In the next section some general recommendations for conservative data analysis are provided. This includes: · · · · Where should data be taken from the CCD Which energy range should be used Which pattern range should be used Which response matrix should be used

For detailed guidelines of XMM data analysis please use the SAS Users ' Guide at http://xmm.vilspa.esa.es/external/xmm_sw_cal/sas_frame.shtml

2.2.1 M OS Imaging modes Source region: where appropriate Background region: · · point source - From the same observation another region of the same area off-axis, away from source counts. extended source - This is more complicated. Please have a look at explanatory notes available on the XMM web site at http://xmm.vilspa.esa.es/ccf/epic/#background.


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Energy range: 0.2-10.0 keV (However, because of calibration uncertainties, care must be taken when interpreting data below 0.3 keV.) In general the user should use patterns 0-12. (see XMM Users Handbook section 3.3.10 available at http://xmm.vilspa.esa.es/external/xmm_user_support/documentation/index.shtml). However, pattern 0 events can be used to minimise the effects (e.g. spectral distortion) of pile-up. Pattern 0 events can also be used for observations in which the best-possible spectral resolution is crucial and the corresponding loss of counts is not important. In addition the user should only use events flagged as "good" b y using (#XMMEA_EM) in the selection expression window of xmmselect. When analysing spectra the user should use arf files produced b y the SAS (version 5.3.0 or above) task arfgen in conjunction with canned redistribution matrices or produce those with the SAS task rmfgen. Timing modes Source region: where appropriate Background region: background subtraction will not usually be an issue for sources observed in timing mode. However because the timing strip is only 100 pixels wide background regions should be taken from the outer CCDs. Energy range: 0.3-10.0 keV Pattern 0 only. As for imaging mode, canned redistribution matrices valid for timing mode will be made available and should be used with arf files produced by the SAS. 2.2.2 PN Imaging modes Source region: where appropriate Background region: · point source - From the same observat tance to the readout node (RAWY) subtracted, because it increases toward out-of-time events from the source, i.e. extended source - see 2.2.1 ion but away from source. Ideally the region should have the same disas the source region. This ensures that similar low-energy noise is s the readout-node. Do not use the columns passing the source to avoid do not use an annulus around the source region.

·

Energy range: 0.15 keV - 15 keV, however both limits depend on readout mode and aim of the analysis. For imaging purposes pattern 0-12 can in principle be used. Since doubles (1-4), triples (5-8) and quadruples (9-12) (see XMM Users Handbook http://xmm.vilspa.esa.es/external/xmm_user_support/documentation/index.shtml) are only and four times the low-energy threshold, respectively, cleanest images are produced by exc above the thresholds. E.g. to produce a 0.2 - 10 keV image one may select singles from doubles only from 0.4 keV. FLAG == 0 omits parts of the detector area like border pixels, etc. This may be not desired (and is unnecessary) in the case of broad-band images. section 3.3.10 availabl created above twice, t luding the energ y range the whole energy band columns with higher of e at hree j us t and fset,

For spectral analysis, response matrices are available only for singles, doubles and singles+doubles. Higher order pattern types are of low statistical significance, have degraded spectral resolution and are therefore not useful. Best spectral resolution is reached by selecting singles for the spectrum. FLAG == 0 should be used for high accuracy to exclude border pixels (and columns with higher offset) for which the pattern type and the total energy is known with significantly lower precision. At high energies the fraction of doubles is however almost as high as that of singles and to include doubles is recommended to increase the statistics. If a sufficient number of counts is available single- and double-spectra can be created separately and fitted simultaneously in XSPEC (with all parameters including norm linked together). One exception is the timing mode (see below). To choose the valid energy band for the spectral fit it is highly recommended to use the task epatplot. It uses as input a spatially selected (source region) event file and plots the fractions of the various patterns as function of energ y. Spectral analysis should only be done in the energ y band(s) where single- (and double-) fractions match the expected curves. In some observations the low-energy noise can be high, restricting the useful band at low energies. Deviations at medium energies indicate pile-up (more doubles than expected) and in such cases the inner part of the PSF in the source region


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should be excluded for spectral analysis. (More information on that topic is available in the XMM Users Handbook at http://xmm.vilspa.esa.es/external/xmm_user_support/documentation/index.shtml). The user should use arf files produced by the SAS (version 5.3.3 or above) task arfgen in conjunction with canned redistribution matrices (which are compatible to the CTI correction used in 5.3.3 or above) or produce those with the SAS task rmfgen. For each readout mode of the PN a set of rmf files is available (for singles, doubles, singles+doubles. Except timing mode where only singles+doubles must be used). The CTI causes a dependence of spectral resolution with distance to the readout node. Therefore the 200 lines of each CCD are divided into areas of 20 lines each (Y0 at readout, Y9 at opposite side, which includes the nominal focus point) and for each area an rmf file is available Timing and Burst modes Source region: Columns around source position Background region: Columns away from source The RAWY coordinate is related to a fine-time, selection timing mode no such selection on RAWY is recommended; by the source. For timing mode only singles+doubles should 0.5 keV to avoid the increased noise. For burst mode singles/doubles as in the window modes. on RAWY will therefore exclude certain time periods. For in burst mode use RAWY < 160 to avoid direct illumination be selected for a spectrum and the fit restricted to energies > energies > 0.4 keV can be used with combinations of