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To confirm the source of the quantum efficiency reduction, here is the same plot, but for fits from the data in the lower corners of the CCD - closest to the framestore. There is no reduction in quantum efficiency for these data, indicating that the drop is due to increased CTI. Increased CTI leads to more charge trailing and more events morphing from acceptible to bad grades. CTI correction (the default in standard processing but not used here), would remove most of the QE drop.
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May 4, 2011
XIS peak location vs Cut Off Rigidity for recent times (201101).
while the last points of xis3 (FI) seem a bit odd, but neither the FI nor the BI are well fit with a line. The peak locations are not a function of the background variations.
Here are plots of the xis1 (BI) high energy count rate vs cut off rigidity to compare to the ACIS s3 (BI) high energy reject rates used to track the background levels for ACIS.
For January 2011: 
For November 2006:
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