Thickness of the contamination of XIS0
Updated 2008-06-18
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.
![Updated Contamination History](/Images/astroe/performance/e0102_rates_20071212.png)
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.
![Updated Contamination History](/Images/astroe/performance/e0102_rates_20071219.png)
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.
![Updated Contamination History](/Images/astroe/performance/contami_20080427.gif)
Figure 3. Same as Figure 1 and 2, showing the change in XIS0 contamination calibration file.
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