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XMM-Newton-NEWS
XMM-Newton-NEWS #26, 15-Nov-2002ESA, XMM-Newton Science Operations Centre atEuropean Space Astronomy Centre (ESAC) P.O. Box - Apdo. 50727, 28080 Madrid, Spain
Contents:
New version of the XMM-Newton Science Archive is now availableVersion 1.5 of the XMM-Newton Science Archive (XSA) is now available. To start the Java-based user interface, please connect to the following URL:http://xmm.esac.esa.int/xsa/ The user interface includes several new functionalities:
http://xmm.esac.esa.int/xsa/docs/tour.shtml together with a list of the known caveats for the current version: http://xmm.esac.esa.int/xsa/docs/xsa_caveats.shtml Since an overwhelming majority of the XMM-Newton data users community has been using the XSA as primary gateway to access their data, XMM-Newton proprietary data will be distributed to their Principal Investigators (PIs) through the science archive only, as of January 1, 2003. PIs interested to have their data on hard media as well can trigger the generation of a CD-ROM through the XSA user interface. The development of the XSA is an ongoing effort. The next public version (2.0) is scheduled for spring-summer 2003. New functionalities expected to be available in future near-term versions of the XSA include:
Do not hesitate to address any questions on the XSA content and functionalities to the XMM-Newton HelpDesk (xmmhelp@sciops.esa.int). We wish you exciting science with the XMM-Newton data! Status of the RGS/MOS coolingIn XMM-Newton News #25, dated 7-Nov-2002, plans to lower the operating temperature of the RGS and MOS CCDs were described, the purpose of the cooling being to move important detector characteristics back towards the values which they had earlier in the mission.Since then, excellent progress has been made in the cooling campaign, with evidence of major improvements in detector performance. The RGS2 instrument was cooled on revolution 532, the MOS1 and MOS2 instruments on revolution 533, and the RGS1 instrument on revolution 537. All operations to change instrument operating temperatures are now completed. An initial appreciation of the results of the cooling can be had by viewing the animated gif movies presented on the XMM-Newton web pages at: http://xmm.esac.esa.int/external/xmm_news/items/cooling02/index.shtml These illustrate the evolution of a number of key parameters during cooling. RGS coolingThrough the night of Sunday to Monday, November 3 to 4, the RGS2 CCDs were cooled towards a new operating temperature of -115 degrees C (RGS Cool_A). The target Mkn 421 was observed through the night to track the effects of the cooling. Towards the end of the night there were strong indications that a slightly higher operating temperature might in fact be needed in order to keep the detectors within the range of active control by the heaters under the full range of possible thermal loading on the instrument radiators. After careful subsequent assessment of the data it was decided to establish the new RGS operating temperature at -110 degrees C.During perigee passage some excursion of the CCD temperature is now seen to a few degrees above the set-point. But the nominal temperature is re-established before resumption of science observations. The main result of cooling for RGS2 is a huge reduction in the incidence of flickering pixels. The CTI has been restored to close to its pre-flight values. Previously poor CTI near the edges of the detectors, where it had been x100 worse than for the inner regions, has been almost eliminated. The CCD noise has been greatly lowered, and the width of the noise distribution peak is now narrower than before launch. There is now just one hot column and one hot pixel in RGS2. During the night of Wednesday to Thursday, November 13 to 14, the RGS1 CCDs were also cooled to -110 degrees C (RGS Cool_B). After preliminary analysis of the data, the improvements in RGS1 performance are found to be entirely consistent with the RGS2 experience. During Cool_B, re-tuning of the RGS CCD transfer clock voltages was also concluded, completing the reconfiguration of the instrument. Where necessary, small refinements of the calibration files needed to handle data obtained in the period between Cool_A (rev.532) and Cool_B (Rev.537) will be provided to users. EPIC MOS coolingThrough the night of Wednesday to Thursday, November 6 to 7, the CCD benches of both MOS instruments were cooled down to the new operating temperature (-120 deg.C), reaching the new value within 2.75 hours.The movies presented on the XMM-Newton web illustrate the reduction of MOS line energy-width as a result of improved charge transfer efficiency and show the decline of thermal defects during cooling. The number of hot pixels has dropped by a factor of 7 (from 167 to 24) for MOS2, and a factor of 2.6 (from 98 to 38) for MOS1. Now, on average only 3 bad pixels are seen per CCD. The charge transfer efficiency has improved by a factor of between 2 and 3, depending on the CCD. The line-width and peak-height of spectral lines has improved markedly. (Note: while the line widths are still being quantified for the Rev.534 post-cooling measurements, the earlier trial cooling of MOS2 in June of this year showed, for example, that the Mn K-alpha line FWHM changed from 160eV to 140eV upon cooling). Currently, the MOS CCDs undergo a temperature excursion during perigee passage. They return to the new nominal operating temperature of -120 degrees C before the re-opening of the science window. There is a seasonal variation in the thermal excursion and we are near, but not at, the peak. This is unlikely to pose any problem for the instrument science operations. Redefinition of the calibration is proceeding on schedule. Impacts of cooling on product distribution from SSCIn planning the cooling exercise, we have striven to keep any consequent impacts on product distribution to a minimum. There is a scheduled hold on product distribution from SSC in the period from mid-November to mid-December to allow the derivation by the SOC and PI teams of new, post-cooling, calibration files (CCFs) and consequent revalidation of the processing chain. (The latest pre-cooling ODFs (those from Rev.531) were exported from SOC to SSC on November 12, and these will be the last ODFs processed with the pre-cooling calibration files.)The definitive re-calibration for the cooled RGSs will now come from scheduled calibrations on Rev.546 (December 1 to 2). SSC product distribution is expected to resume before Christmas, using preliminary "cold" CCFs for RGS. Monitoring for contaminationSpecific contamination monitoring observations are underway to address the remote possibility that, after cooling the detectors, any low level ambient contaminants within the telescope/focal-plane subsystem might start to freeze out onto the cold detector surfaces, although these are still NOT the coldest points in the system by a significant margin. In the event of any contamination appearing counter-measures will be taken immediately.Prospects for the end resultWhile intensive work is ongoing to fully evaluate changes in the instrument performances following cooling, all indications are that the exercise has been, as anticipated, extremely beneficial, with major improvements in several key performance parameters.The original hope that the RGS and EPIC MOS instruments would see key performance characteristics restored to values which they had early, or much earlier, in the mission, appears to be borne out. Yours sincerely, XMM-Newton SOC |
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