Major Improvements in Version 2 Processing
Version 2.X processing of Suzaku data incorporates following two major updates. Other, more detailed, improvements of Version 2.X processing are described in the V2.0.6.13 documentation page.
1. Calibration of XIS data with Spaced-row Charge Injection (SCI)
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).
In Version 1.X processed data, there is a time-dependent attitude
wobble of 30-60 arcsec, which is synchronized with the orbital period
of the Suzaku satellite (96 min). This is thought to be
due to thermal distortion affecting the relative orientations of the
scientific instruments and the star trackers. This thermal wobbling
significantly broadens the image core and leads to errors in derived
source positions.
An empirical correction method has been developed, and coded in the
form of a new tool, aeattcor. In Version 2.X processed data,
this tool has been run on the attitude file before it is applied to
the event data. That is, users of Version 2.X processed data need not
take any additional action, while Version 1.X data users can apply this
correction by updating the attitude file using aeattcor and applying
it to the event files. This method has been verified to sharpen the source
images and reduce the source position errors from 60" to 20". More
details of the empirical correction can be found in
Suzaku Memo 2007-04.
2. Empirical Modelling of Thermal Wobbling of Attitude
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