In-Orbit Performance of the EPIC-PN CCD-Camera on Board XMM-.Newton Ulrich. G. Briela, B. Aschenbach'1, M. Ba1asinF, H. Brauningera, W. Burkerta, K. Dennerla, M. Eh1e' F. Haberla, R. Hartmanna, G. Hartner', . Hollc, P. Massad, N. Meidingera, J. Kemmerc E. Kendziorrab, M. Kirsch', N. Krause', M. Kusterb, D. Lumbe, E. Pfeffermann', J. Paib w. Pietsch", M. Poppa, A. Read', C. Reppin", H. Soltauc, R. Staubertb L. Strüdera, J. Trümpera, G. Villad, Ch. v. Zanthier', V. E. Zavlina aMaxplaflckjflstjtut für extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, Germany blnstitut für Astronomie und Astrophysik der Universität Tflbingen, Abteilung Astronomie, Waldhäuser Strasse 64, 72076 Tübingen, Germany CKETEK GmbH, Am Isarbach 30, 85764 Oberschleif3heim, Germany dlstituto di Fisica Cosmica "G. Occhialini" Via Bassini 15, 20133 Milano, Italy eEuropeafl Space Research and Technology Center 2200 AG Noordwijk zh, the Netherlands ABSTRACT On December 1999, the European X-ray satellite XMM, now called XMM-Newton, was successfully put into orbit. After initial commissioning of the satellite's subsystems, the EPIC-pn camera was switched on and tested thoroughly in the period Jan./Febr. 2000. After refining of some of the parameter settings and the on-bord pn- computer programs, we started the Calibration and Performance Verification Phase, which will last until the end of May 2000. In this paper we report on the results of the EPIC-pn Commissioning Phase with respect to the in-orbit perfor- mance of the camera. We also show some of the early results with the pn-camera, the first light image of a region in the Large Magellanic Cloud, and an observation of the Crab Nebular. Keywords: XMM-Newton, pn-CCD, X-ray detector 1. INTRODUCTION XMM-Newton, the X-ray Multi Mirror Mission1 is the second cornerstone project of ESA's Horizon 2000 program. It was successfully launched at the 10th December 1999 from Kourou/French Guyana with the first commercial Ariane V launch vehicle. The X-ray payload essentially consists of 3 imaging Wolter type I telescopes, operating in the energy range from 0.1 to 15 keV. The highly nested mirror modules2 have a focal length of 7.5 m, a half energy width of better than 15 arcsec and a total effective area of 4400 cm2, both for 1.5 keV. About 50% of the X-ray light of two telescopes is dispersed by reflection grating spectrometers3 to achieve higher spectral resolution. The European Photon Imaging Camera (EPIC)4 collaboration supplied the focal plane instrumentation for XMM, which is based on CCD technology. Two MOS CCD detectors5 are placed in the focus of the two telescopes equiped with the reflection gratings. In the focus of the third telescope is a pn-CCD detector making use of the full aperture of the mirror system. This camera was designed, developed and tested in our institutes. In X-Ray Optics, Instruments, and Missions III, Joachim E. Trumper, Bernd Aschenbach, Editors, 154 Proceedings of SPIE Vol. 4012 (2000) • 0277-786X/00/$1 5.00 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/27/2014 Terms of Use: http://spiedl.org/terms
Transcript
In-Orbit Performance of the EPIC-PN CCD-Cameraon Board XMM-.Newton
Ulrich. G. Briela, B. Aschenbach'1, M. Ba1asinF, H. Brauningera, W. Burkerta, K. Dennerla, M. Eh1e'F. Haberla, R. Hartmanna, G. Hartner', . Hollc, P. Massad, N. Meidingera, J. Kemmerc
E. Kendziorrab, M. Kirsch', N. Krause', M. Kusterb, D. Lumbe, E. Pfeffermann', J. Paibw. Pietsch", M. Poppa, A. Read', C. Reppin", H. Soltauc, R. Staubertb
L. Strüdera, J. Trümpera, G. Villad, Ch. v. Zanthier', V. E. Zavlina
aMaxplaflckjflstjtut für extraterrestrische Physik,Giessenbachstrasse, 85748 Garching, Germany
blnstitut für Astronomie und Astrophysik der Universität Tflbingen,Abteilung Astronomie, Waldhäuser Strasse 64, 72076 Tübingen, Germany
CKETEK GmbH, Am Isarbach 30, 85764 Oberschleif3heim, Germany
eEuropeafl Space Research and Technology Center2200 AG Noordwijk zh, the Netherlands
ABSTRACTOn December 1999, the European X-ray satellite XMM, now called XMM-Newton, was successfully put intoorbit. After initial commissioning of the satellite's subsystems, the EPIC-pn camera was switched on and testedthoroughly in the period Jan./Febr. 2000. After refining of some of the parameter settings and the on-bord pn-computer programs, we started the Calibration and Performance Verification Phase, which will last until the end ofMay 2000.
In this paper we report on the results of the EPIC-pn Commissioning Phase with respect to the in-orbit perfor-mance of the camera. We also show some of the early results with the pn-camera, the first light image of a region inthe Large Magellanic Cloud, and an observation of the Crab Nebular.
Keywords: XMM-Newton, pn-CCD, X-ray detector
1. INTRODUCTIONXMM-Newton, the X-ray Multi Mirror Mission1 is the second cornerstone project of ESA's Horizon 2000 program. Itwas successfully launched at the 10th December 1999 from Kourou/French Guyana with the first commercial ArianeV launch vehicle. The X-ray payload essentially consists of 3 imaging Wolter type I telescopes, operating in theenergy range from 0.1 to 15 keV. The highly nested mirror modules2 have a focal length of 7.5 m, a half energywidth of better than 15 arcsec and a total effective area of 4400 cm2, both for 1.5 keV. About 50% of the X-raylight of two telescopes is dispersed by reflection grating spectrometers3 to achieve higher spectral resolution. TheEuropean Photon Imaging Camera (EPIC)4 collaboration supplied the focal plane instrumentation for XMM, whichis based on CCD technology. Two MOS CCD detectors5 are placed in the focus of the two telescopes equiped withthe reflection gratings. In the focus of the third telescope is a pn-CCD detector making use of the full aperture ofthe mirror system. This camera was designed, developed and tested in our institutes.
In X-Ray Optics, Instruments, and Missions III, Joachim E. Trumper, Bernd Aschenbach, Editors,154 Proceedings of SPIE Vol. 4012 (2000) • 0277-786X/00/$1 5.00
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2. DETECTOR DESCRIPTION AND READ-OUT MODESThe heart of the pn camera is a 4 inch silicon wafer divided iii an array of 12 rn()ilolit iiicallv iiitegiat ed pii—CCDdeveloped and manufactured in our semiconductor laboratory •c The sensitive area of the (anieril is 6 ciii x (i ciiieach single CCD has a dimension of 1 cm x 3 ciii. The pixel size of the CCDs is 50 tni x 150 tin, trruigedin 200rows by 64 channels. At a focal length of 7.5 rn of the XM\1 mirror module the pixel size (orrespoilds to an angularresolution element of 4.1 arcsec. Tue CCD is run iii the back—illuiuiiiatioii mode. has ii very thin elitrinice wiiidwand is fully depleted with a depletion depth of 300 tim. This results in a quantum effl(ielIcV of iriore tlaui St ) iii I lieenergy range from 0.2 to 10 keV. A detailed description of the wafer as well as of the camera (au be hund iii Ref. 7and 8 Figure 1 is a photograph of the assembled camera.
Figure 1. Photograph of the assembled EPIC-pn camera.
A variety of read-out modes allow to adjust the detector performance to the observational requirements of thecelestial sources: imaging modes utilizing the highest positional resolution, arid fast, modes to achieve a better timeresolution at the expense of the coordinate in shift direction.
In full frame mode all 12 CCDs are read out sequentially in about 73 msec, winch also is the time resolution ofthis mode. Point, sources not brighter than 0.7 mCrah can be observed without, running into the problem of pile-up.Since the pn detector is not a 'frame store' device, the CCD is sensitive to X-rays also (luring read-out times, causingthe so called 'out-of-time' events. These are events recorded during the read-out phase of time CCD when the chargecontent of the registers is shifted towards the read-out anodes. Given by the ratio of read-out to integration time.the fraction of the out-of-time events is approx. 7%. The integration time in the full frame mode can be extendedto 200 msec, reducing this fraction to nearly 2.5%.
Two window modes allow to simulate a frame store operation: in the Large Window mode 100 rows of each CCDare read out after they have been fast shifted into the 'store region', the 100 rows near the read-out, anode. Thisoperation reduces the out-of-time fraction to about 0.3%. Reading out all 12 CCDs in Large Window mode, the readout area of the detector is reduced to 3 cm x 6 cm. Because of an integration time of 48 msec. the possible pointsource strength without pile-up is 1.1 mCrab. In the Small \Vindow mode 64 rows of CCD 0 of quadrant 1 are readout after an integration time of only 5.7 msec. This allows a source strength of about 11 rnCrab at an out-of-tunefraction of about 2%. The read out area is only 1 cm2, but still large enough to collect more than 98% of the flux ofa point source.
For the observation of even brighter point sources and/or if a time resolution of better than a few mnsec is required,the pn-CCD can be operated in special fast read-out modes, where the shorter read-out times are acluevel on theexpense of a loss of spatial resolution along the shift direction. Two different fast, read-out, modes are iniplemriented,the so-called Tuning and Burst modes. In both cases only CCD 0 of quadrant 1 is read out.
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In Timing mode the CCD is read continuously, while integrating the charges from groups of 10 pixels for eachcolumn along the shift direction, resulting in 64 macro pixels of 0.15 mm x 1.5 mm each per line. These macro linesare further processed like normal lines. After 200 macro lines a time word is generated, which records the frame timerelative to the space craft time with 5.96 msec resolution. Using the position information along the shift directionone can further increase the time resolution of events from point sources to 29.5 ,usec. The allowed source strengthis about 0.15 Crab.
To avoid pile-up for very bright sources (> 0.2 Crab), they must be observed in Burst mode, where the CCDis used like an analogue transient recorder for very short observation intervals separated by much longer read-outintervals. In each cycle 200 lines are fast shifted towards the anodes at a speed of 0.72 ,usec/line. Afterwards theCCD is read out at normal speed (like in imaging modes), resulting in an effective exposure time (life time) of only3%. Like in Timing mode one can use the position along the shift direction to increase the time resolution of eventsfrom point sources to 2.9 sec. During read-out, the area under the PSF is exposed for a much longer time, thusgiving rise to pile-up. Therefore only the first 180 lines of the CCD are read. A more detailed description of thepn-CCD read-out modes can be found in Ref. 9 and 10.
3. EPIC-PN COMMISSIONING PHASESoon after the launch of XMM-Newton, the commissioning of the instruments was started. Following an initialswitch-on of the EPIC-pn electronics, a functional check-out was successfully performed. After the first critical task,the opening of the internal camera door, the CCD temperature was raised to about 0°C for more than 48 hours toallow for outgassing. At the 16th of January 2000, the CCDs were cooled down to their operating temperature of-90°C and subseqently switched on for the first time in orbit, monitoring the internal calibration source, a Fe-55radioactive source (Mn-K at 5.9 and 6.4 keV) with an additional Al-target (yielding fiourescent Al-K photons at1.5 keV). Despite some problems with CCD1 of quadrant 2 we had experienced prelaunch during warmtests, all 12CCDs worked nominally. We exercised all different read-out modes and fine-tuned some of the set-up sequences. Inaddition, observations were performed in the so-called "low gain mode" ,in which spectra of events up to 300 keV canbe recorded. The goal was to investigate the soft proton flux during solar flares, an potential risk for front-illuminatedCCDs like the EPIC MOS camera. These tests are described and discussed in the paper by Strflder et al.1'
The particle environment in space is different from that on ground. The flux of minimum ionising particles(MIPs) is about 2.5 particles/cm2/sec, more than a factor of 2 higher than expected. Furthermore due to thedifferent particle composition and energy spectra in orbit we have events with much higher energy losses in theCCDs than seen on ground. These events disturb the onboard calculation of the offset maps, which are needed forthe on-board event detection (see previous paper by Kendziorra et al9),leading to numerous regions in the maps withan incorrect (too low by up to 50 eV) offset value. As result, these regions produce many noise events which normalyare below the event threshold, and hence lead to a too high counting rate (telemetry rate) . They also reduce theenergy resolution of the CCD, because the difference between the wrong and the correct offset is added to the eventsignal. Secondly, the on-board MIP rejection efficiency was only about 80%, leading again to an increase in telemetryrate. The transmitted events, caused by particles, can of course be rejected on ground, using the same criteria fortheir rejection (see previous paper by Kendziorra et a19).
Fortunately, the spare EPIC pn-camera was setup and running in the Panter test facility and immediate testscould be performed, exposing the CCDs to 5 MeV alpha particles. The same behaviour of the camera was found anddetailed investigations resulted in a modified software program for the calculation of the offset maps. The new s/w-patch produces clean offset maps while exposing the CCD to the 5 MeV alpha particles. In addition, the processingparameters of the particle rejection program could be optimized during the tests. The new s/w-patch was successfullyloaded to the space-craft and, together with the new parameter setting, tested in time for the calibration/verificationphase of XMM-Newton. As described in the next chapters, the performance of the camera is now nearly identicalto the pre-flight results, except that we have to discard the first 10 rows (of 200) close to the read-out node. Thisagain is caused by the much higher energy losses from low energy particles in the MeV energy range.
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4.1. Background4. IN-ORBIT PERFORMANCE
i3esicles the background produced by particles as descibed above. there are different additional sources of backgroundin the detector. Intruisic to the CCDs are 'hot pixels or even hot columns, which produce noise events iii e;uh read-out fraiiie. During ground calibration, we determined these pixels/columns and created a so called 101(1 piXel/(0liiIililniap" (BPM) whicli is loaded into the experiment computer arid used to prevent events froni those pixel/ioluniristo be t ransinitted to ground. First in—orbit tests verified that this BPM is still valid, and we consequently (dli 1151' iialso iii orbit. 0niy 12 single pixels have to be renioved, dull in S (oluIiilis we have to introduce an offset shift (evKern iziorra ci al for a detailed description).
We performed long observations with the filter wheel in closed position to gather the reso lual backgrouroi in I in'detector, partly caused by flourescent X—ravs front the material of the (let ectOr housing etc. Iii Fig. 2 WI' show I in'distribution of singles plus recombined events across the detector. (Split events are recoriibined tI I 0111 ('\'('ilt aridassigned to the pixel with the rnaxirnuni amplitude). The border pixels between the top and hoti on (1I1adri1it showii higher density of events since these pixels, for technical reasons, have a SiZe of 150iiii x 2U0ini. Besides t Intl .till'background events are spread homogeniousiv across the detector.
Figure 2. Image of residual background, taken with the filter wheel in closed position.Indicated is the dimension of the detector in cm as well as in arcrnin, using the focal lengthof the XMM mirror.
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C0c\j0000()a)Cl)CCCl)
C)Cl)
E 1 [key] 10
cJCEC)
>a)
Cl)
(1)G)C)CCl)
Figure 3. Spectrum of residual background, taken with the filter wheel in closed position.Indicated are energies of characteristic X-ray lines.
In Fig. 3 we show the spectrum of the single events. We find three components: a flat spectrum between 0.3 and15 keY with an intensity of less than i03 singles/sec/keV/arcmin2, an up to two orders of magnitude increase ofintensity towards smaller energies, and a series of intense resonant scattered X-ray lines from the material around theCCDs, the strongest being Al-K and Cu-K. Aluminum is the material of the housing of the camera. An image usingjust photons of Al-K energies show no variation in intensity over the CCDs. Different is an image using photonsof Cu-K energies: those photons mainly come from the printed circuit board (with contains copper) located closelybehind the CCD-wafer. For outgassing reasons this board has an approx. 15mm diameter whole in the middle, whichis seen in the Cu-K photon image.
500
400
300
200
100
0
Figure 4. EPIC-pn counting rate of the XMM-EPIC pn observation of the Hickson Group16. Shown is the number of single events/lOOsec of the CCD2 of quadrant 0, which containsessentially no X-ray source.
10000 20000 30000 40000 50000
time [sec]
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\Vith the filter wheel positioned to use one of the filters, the background increases: We find the galactic/ext ra—galactic X—ray background and in addition a background component which is strongly varying in t line. Figure 4is a graph of the counting rate of the XMM-EPIC pn observation of the Hickson Group 16. Shown is the numberof single events/ lOOsec of the CCD2 of quadrant. 0, which tor that observation contains essetmtiallv no X—ray source(see Fig. 5). As can be seen, the background rate varies hr moore than a factor of 50. Figure 5 left panel. is anpn—image of this Hickson field. accuminulated only during times with the low background rate, as it is imidicatedin the rate plot (Fig. 1) by light—hatched times. Besides the strong sources in the center of time field, whelm aregalaxies from the Hickson group. we find more than 80 faint. sources. In o'ont rast . t lie ililage aecuitimimmulated duringhigh background ( bold—hatched times iii Fig. 4) unIv shows the 10 strongest sources, as seemi in Fig. 5, right panel)Cutting out of both images the regions of all the visible sources in Fig 5. we directly ('an ('olumpame the I aekgrourmdspectra. Both spectra, normalized to sec. keV and arcmiun are shown iii Fig. 6. During low ho'kgrotmiul. we fin(l anaverage intensity of about 2 x lo3singles/sec/kev/arcmniri2 at 1 keV, whereas during high background. this averageimiteiisity went up hr a factor 10. \Vlule we still see all the instrument background lines during l( )W ha.ekgmotmnd , onlyhe strung Cu—K is seen during lugh background.
Figure 5. EPIC-pn image of the Hickson Group 16 field in detector coordinates, accummulated duringtimes with low background rate (left panel) and high background rate (right panel).
Figure 6. EPIC-pn spectra of the Hickson Group 16 field, accummulated during tiimies with low back-ground rate (left panel) and high background rate (right panel).
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We have several indications to believe that this additional background is mainly caused by soft protons, reachingthe detector through the telescope. Binning the background in concentric rings, centered at the telescope on-axisposition, we find the telescope vignetting in the galactic/extragalactic background as a drop in flux of about 35%between 7 and 14 armin, consistent with theoretical expectations of the vignetting (closer to on-axis we probablysee both, vignetting and source emission). These ring-fluxes are plotted in Fig. 7 as the lower crosses of the plot.For high background we find a different vignetting curve: the upper crosses are the corresponding ring-fluxes aftersubtracting the flux during low background. The drop in flux of this additional component is still significant, but onlyabout 15%, again comparing 7 and 14 arcmin off-axis. If this component was made of X-rays, then their vignettingcurve should be the same as for the galactic/extragalactic background, hence most of it cannot be X-rays. Butsince this component does show vignetting, it has to come trough the telescope, but is not specularly reflected offthe mirror. Protons with energies up to 300 keV experience scattering on surfaces: they are scattered in a finiteangle, hence their vignetting is less pronounced compared with photons. Therefore low energy protons (of variableintensity) could explain this additional background component. More indications for protons being the cause of thisbackground can be found in the paper by L. Strüder et al."
10 I—.- I
_14off-axis angle [arcmin]
Figure 7. Vignetting curve of different backgrounds: lower crosses from background duringlow background rates; upper crosses from background during high background rate, valuesof lower curve subtracted. The hight of the crosses indicate a
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4.2. Charge Transfer EfficiencyThe charge transfer efficiency (CTE) of the pn camera is not as good as the GTE of the MOS CCDs. By a hugecalibration effort we were able to measure, understand and model the GTE in order to correct for GTE losses (formore information refer to the papers by N. Krause et al'2 and K. Dennerl et al'3). After the experience with theUs satellite Ghandra, where especially the front illuminated GGDs are very susceptible to soft protons which causetheir GTE to degrade we are also concerned about any degradation of the pn GGDs. Although the pn GGDs areback-side illuminated, we took any possible counter measures to prevent high proton doses: during the satellite'spassages through the radiation belts, we close the filter wheel. And in addition we also close the filter wheel incase the on-board radiation monitor detects a flux above a certain value. With the on-board calibration source wemonitor regularly the GTE of our GGDs. So far we have not detected any degradation of the GTE. The correctionfiles, obtained at ground during the calibration campains, are still valid.
C
C
.'0
C
C00
Figure 8. EPIG-pn spectrum of single events of a very long (s43hours) exposure with theinternal calibration source shining at the detector with the filter wheel in closed position.
4.3. Detector Response MatrixAs for the GTE, the detector response matrix (DRM) was extensively calibrated on ground during our calibrationcampaign at the synchrotron facility in Orsay (for more information refer to the paper by M. Popp et al14) Wecan use the internal calibration source and the additional, instrument related flourescent lines to verify the DRM. InFig. 8 we show the spectrum of single events of a very long (43 hours) exposure with the calibration source shiningat the detector and with the filter wheel in closed position. The events are corrected for GTE losses. Besides thecharacteristic lines of the source (AL-K, Mn-KC,) we find flourescent lines of all the material around the detector.In addition we see the escape peak of the strong Mn-Ku and a continuum radiation up to about 10 keV. Altogetherwe find a reasonable good fit of the data to a model spectrum including 11 lines folded with the DRM. The resultingmodel is also plotted in Fig 8 as line. The current version of the DRM does not yet take into account the slightlyhigher event threshold used in orbit (100 eV instead of 80-90 eV used for the ground calibrations), which influencesthe number of "pseudo" singles (doubles are recognized as singles when the smaller companion falls below the energythreshold). Deviations of the model from the data, especially at the foot of the strong lines, are caused by thepseudo singles (on the low-energy part of the lines) and by "out-of-time" events, which do not have the correctGTE-correction. We used only the central 40 lines of the GGDs (maximum distance to the electronic read-out) tominimize the number of out-of-time events which in this case are found on the high-energy part of the lines.
161
Z() OC)
0.5 1 2 5 10Channel Energy (keV)
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5.1. First Light5. EARLY RESULTS
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During the commissioning phase, after we had the first tests with the internal calibration source, we performed theso-called "first light", the first observation done with XMM-EPIC. A suitable target to show the power of XMM is aregion in our neighbouring galaxy, the Large Magellanic Cloud (LMC), because of its variety of different objects: itcontains Stars, Supernova Remnants, the well known Supernova 1987A and in addition diffuse X-ray emission fromthe hot gas in the LMC.
Figure 9. EPIC-pn first light: color image of the Large Magellanic Cloud.
The color image (Fig. 9) is the preliminary result of our first light observation of about 15 hours integration time,taken at the 1gth of January 2000. The field of view corresponds to about the size of the full moon. In order toshow the power of XMM, we display the different X-ray energies in different colours. Red corresponds to soft X-rayenergies (0.3 - 0.75 keV), green to medium energies (0.75 - 1.5 keV) and blue to hard energies (1.5 - 5 keV). If theX-rays originate from hot plasma, these colours span a range of plasma temperatures from about 106 °C to 108 °C
One of the exciting sources in the field is the Supernova 1987A, seen as point source at the lower right side inthe image. This source is the youngest Supernova in our immediate neighbourhood, at a distance of only 160000Lightyears. The brightest source in the field, left from the middle, is a very old Supernova Remnant with a fastrotating Neutron Star inside. Such a Neutron Star is also expected in 1987A, but so far has not been detected yet.
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Tue big colourful ringlike struct ure iii the center of the ililage is especially interestiiig for its different o1oiir.The blue part must he much hotter than the red part. This object is probably also a Supernova Reriiiiiuit., hut tinastonishing fact is. that it. shows different temperatures in its ring. \Vit,h t lie ver good spectrosc(piclll capal)ili iesof XMM regions like those can now be investigated ill (let au.
Also new are the blue (X—ray hard) point, sources iii the center of t lie image. '\e can see t Iueiii Dilly because ofthe large collecting area of tile telescopes. especially at. the higlier X—ray energies. 'lliese s nirces pro})luhlv (1(1 no!belong tic the [MC. They are likely to be active galaxies or quasar. located ver deep in space behind t lie 1.'\l('.5.2. Observation of the Crab Supernova Remnant in Burst Mode(in Feb. 2€0 t lie Crab has been successfully observed wit ii t lie EPIC pn-CC'D c;uner;u iii Burst iuic eli for 7 ksec.Figure 10. left panel, shows an intensity image of all event s from this exposure. ( )iue nlearlv sees the expect ed out —of—tune signature of an extended object with a brighter point source (the pulsar). It is also obvious from this iiuiilgcthat at least the first 20 lines close to the focal point are still contaminated by Pile—ui) (luring read—out - Iii ordero sei ) arat e events fran i the pulsar as much as poss 11)1 e froi n t. I iose fron i t.I a ii ('1) ul t. we ha v ccii lv select ((1 c veii Is
froiui lines 1 to 160 from the three most intense coluniiis. \Vc have perforruied a preliminary (applying no baryccnt iiccorrection) timing analysis for these events. Ihe whole observation was divided ilito i parts of I ksec diii at ion each.The pulse periods derived from a maximum period analysis vary bet weeti 33.510196 ins arid 33.510229 ins, whichis Consistent wit Ii a constant period. giveli the expected statistical accuracy of t).00007 ins. Thin right panel of Fig. 11)shows the resulting pulse profile for a period of 33.51 (t2t) ins, which ciearly (lemons! rates the excellent t.iiiie resolutionof the pni-CCD camera.
Figure 10. Left panel: Intensity image of the Crab Supernova Remnant, observed with thin EPIC-pucamera in Burst Mode. Right panel: Deduced pulse profile of the Crab pulsar.
6. CONCLUSIONSThe EPIC-pn detector, one of the imaging cameras of the recently launched XMM-Newt.on X-ray satellite, is stic-cessfully commissioned. Its in—orbit perforniance is as excellent as is was predicted frorii ground calibrations andtests. Only minor modifications of the on—board soft—ware aiid of some of t lie inst.runient set—ups hinl t,o In' iuiitde.Although the in—orbit background is somewhat, higher than expected, the first—light, image of a region in the LargeMagellanic Cloud and the observation of the Crab pulsar show the great power of the instrunuent.
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7. ACKNOWLEDGEMENTSMany people have contributed to the design, manufacturing, test and calibration of the pn-CCD camera. We wouldlike to thank all our colleagues from all participating institutions. We especially thank the staff of the XMM-NewtonScience Operation Center at VILSPA (Spain) and the Mission Operation Center at ESOC (Germany) for theirsupport during the commissioning phase.EPIC-pn is supported by the Deutsches Zentrum für Luft und Raumfahrt (DLR) under contract No. 50 OX 93025/-XMM-EPIC and by the EUROPEAN SPACE AGENCY under contract No. 8873/90/NL/PB(SC).
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