Accumulated radiation damage inevitably compromises the performance of CCD chips in-orbit. This can be mitigated by operating the CCDs with Spaced-row Charge Injection (SCI), which was made available to Suzaku observations starting in the fall of 2006 and is now (since start of the AO-2 observations) the default.
Although the improvement in spectral resolution was confirmed during the test period, Version 1.X processing was carried out with older versions of software and calibration files that cannot account for the effects of SCI on XIS data. In particular, the PI values in Version 1.X XIS files are incorrect for observations with SCI.
Version 2 processing incoroporates the calibration of SCI, so that PI values are correct, and a keyword has been added to indicate whether XIS was operated with or without SCI. The response generator, xisrmfgen reads this keyword and automatically generates appropriate RMF files. Moreover, the reduction in effective area that accompanies improved spectral resolution can be reflected in the ancilary response files by using xisexpmapgen (new tool) and xissimarfgen (updated).
More details will be found in the Suzaku Memo 2007-06.