Thickness of the contamination of XIS0
The XIS team has found that the contamination of XIS0 is increasing more rapidly than expected.
Figure 1 shows the history of the contamination thickness evaluated from the regular observations of E0102-72.3, including the latest one on December 1st-2nd 2007. Solid curves represent the model for the time evolution of the contamination thickness in files ae_xi?_contami_20070920.fits in the CALDB. The contamination thickness of XIS0 shows more rapid increase than that expected from this model. Accordingly, arfs generated with xissimarfgen with CALDB versions 2007-12-04 and older might underestimate the efficiency degradation by the contamination for the XIS0 data obtained after April 2007. The amount of the underestimation can be estimated from Figure 1.
Figure 1. History of the contamination thickness evaluated from repeated observations of E0102-72.3. Solid lines represent the model of contamination evolution in ae_xi?_contami_20070920.fits files found in the CALDB, while the dotted lines the earlier model of ae_xi?_contami_20061016.fits. Note that all the data points in the figure are based on the analysis of ver2.x products and slightly differ from those shown in the Technical Description for AO-3 proposers.
We have delievered the updated calibration files, which are now available as part of the 2008-01-13 release of CALDB. Users analyzing XIS data taken since 2007 Apr should regenerate the ARF file using this release of CALDB.
Figure 2. Same as Figure 1, except the solid lines represent the updated model of contamination evolution in ae_xi?_contami_20071224.fits files found in the 2008-01-13 release of CALDB.
We have further delivered an updated calibration file for XIS0 as part of the 2008-06-02 release of CALDB. This update is unrelated to the problem of quantum effieincy calibration files and is still available and should be used.
Figure 3. Same as Figure 1 and 2, showing the change in XIS0 contamination calibration file.
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