XIS Contaminant Calibration Updates
Oct 15, 2012
Latest Update
The 20120902 version of Suzaku XIS CALDB includes updated calibration files (ae_xi?_contami_20120719.fits) for the XIS contaminant build-up. These represent a significant improvement in the calibration of the low energy response of the XIS.
For the center of the XIS FOV, the time dependence of the chemical composition of the contaminant was revised now including nitrogen for XIS1. The XIS team has revised the spectral models for E0102-72 and RX J1856.5-3754, included PKS 2155-304 observations, and analyzed newer calibration observations obtained since the previous release.
Figure showing 2011 Apr 26 observation of PKS 2155-304 fitted using (a) old and (b) new models of the contaminant.
The model of the spatial distribution of contaminant was also updated. In addition to the use of the new model for the contaminant build-up at the center of the instrument, and the use of the recent calibration observations, the parameter for the spatial distribution is now allowed to vary over time.
Figure showing 2012 Jun 11 observation of the Cygnus Loop fitted using (a) old and (b) new models of the contaminant.
xissimarfgen and xisarfgen both use the latest contamination calibration files automatically default. All users, particularly those analyzing data obtained within the last year or two, are strongly urged to re-generate the arf files (no other steps need to be repeated) which will improve the fit accuracy and may allow use of the data to lower energy than was possible previously.
Note that the functional form of the contamination model, used by xissimarfgen and xiscontamicalc, was updated in Version 18 of Suzaku FTOOLS, released in 2011 June. Users of older versions of FTOOLS (which assumed a fixed contaminant composition, with C/O=6) cannot take advantage of the newer calibration files.
For the record - Older update (2008 Jun 18)
The thickness of contamination for XIS0 is increasing more rapidly than the model in the calibration file in CALDB releases 07-12-04 (XIS Calibration Files: 20071122) and older. Spectral fits to recent XIS0 data using response files created using these contamination calibration files will therefore "detect" excess NH.
Updated calibration has been released in the 2008-01-13 release of CALDB (XIS Files 20080113), and a further update for XIS0 is in the 2008-06-02 release of CALDB (this is unaffected by other problems). Read details.
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