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Suzaku Guest Observer Facility

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).

2. Empirical Modelling of Thermal Wobbling of Attitude

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.

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This file was last modified on Wednesday, 20-Oct-2021 08:41:31 EDT

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