Things to Watch Out For
Last Updated Mar 28, 2008
Most V1.x to V2.x transition issues are believed to have been solved.
- All Suzaku observations have been (re)processed with V2.x.
- HXD/PIN background files have been released. Although most observations are covered by the released files, there area few periods for which V1.2 background files are recommended over the V2 files (see note below). (updated 2007 Dec 27)
- HXD/GSO background files have been released.
- XIS night earth background database and tool have been release.
- There is a new version of the ABC guide that corresponds to V2.x data anlysis, although it does not yet include the description of GSO data analysis.
The remainder of this page documents the known calibration and software issues.
1. Calibration Issues
ISAS maintains the calibration status and caveats pages.
In addition, we note the following items:
- HXD/PIN - XIS Cross Normalization (Updated 2007 Nov 29)
- With Version 2 data, the normalization of PIN data relative to XIS0 data is 1.06-1.09 for observations of the Crab at the XIS nominal position, and 1.11-1.13 for those at the HXD nominal position. The rangees are for use of different energy bands for the PIN data. See Suzaku Memo 2007-11 for details.
- XIS: Energy scale and resolution calibration as verified using the 55Fe calibration soruce
- SCI data processed using V2.1.6.15 and earlier versions: After 2006 September, the gain at Mn K alpha line decreased at a rate of 30 eV/year in the FI chips and 50 eV/year in the BI chip. See notes on V2.0/2.1 processed XIS data for more. Also read about updated calibration.
- Non-SCI data: The energy scale is well calibrated untill July 2006 in FI units, but systematically higher by 10 eV in XIS1. After this time, gain gradually increased in XIS3, rapidly decreased in XIS0 and XIS2, and gradually decreased in XIS1.
- 2x2 mode (non-SCI): With the current calibration, there is an offset in the 2x2 mode energy scale relative to the 5x5 mode. This offset is sensor, time, and energy dependent.
- For full details, see XRT/XIS Energy scale page at ISAS.
- XIS: Flux calibration for small extraction regions (users of data with
1/4 Window or 1/8 Window options are likely to be affected).
- XIS flux calibration is most accurate for large, circular
extraction regions centered on the source. For example, a radius
of 250 pixels (260 asrcsec) ensures that 99% of the flux of a point
source is included in the extraction region. Users should use a
large extraction region if at all possible.
The current calibration is noticeably less accurate for small extraction regions. This is not a major issue for r>150 arcsec (agreement among sensors to better than a few %), but becomes serious for r<100 arcsec. For 50 arcsec region, XIS1 in particular will measure fluxes that are 20-30% lower than it should (XIS0 appears most reliable in this respect, followed by XIS3 and XIS2).
The XRT and XIS teams are working on refinement of the PSF and the effective area calibrations that will improve the situation. However, because of the interaction of two instruments and two calibration items, this is proving to be a time-consuming process.
- XIS flux calibration is most accurate for large, circular
extraction regions centered on the source. For example, a radius
of 250 pixels (260 asrcsec) ensures that 99% of the flux of a point
source is included in the extraction region. Users should use a
large extraction region if at all possible.
- XIS: Contaminant thickness for XIS0 (Updated 2008 Jan 16)
- The thickness of contamination for XIS0 is increasing more
rapidly than the model in the calibration file in CALDB releases
2007-12-04 (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). Read details.
- The thickness of contamination for XIS0 is increasing more
rapidly than the model in the calibration file in CALDB releases
2007-12-04 (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.
- PIN responses by epoch:
- With V2.x processing, data from all PIN units should be analyzed together. However, due to the changes in bias voltage and the software threshold, response matrices appropriate for the epoch of the observation should be used in spectral fitting.
- V2 PIN background files selected periods (Revised 2007 Dec 27)
- There are two epochs (the initial operation period, up to 2005 September 1, as well as the period 2006 March 23 to May 13, both within epoch 1) during which the V2 PIN non X-ray background (NXB) files are known to show ~10% systematic offset, caused by minor changes of operational parameters. See PIN background page for details.
- Please note that the bgd_d background files to be used for these period need to be deadtime-corrected, unlike PIN background files generated using other models. (added 2008 March 28)
- V2 GSO gain correction for selected period (Added 2008 Jan 16)
- The HXD team has discovered that the GSO gain correction using the current version of hxdpi shows a small discontinuity around 2006 March 3 - 2006 May 9; the energy scale of reprocessed data becomes different by several % from that of response and background. HXD team is now developing the new version hxdpi.
- Reproducibility of HXD non X-ray background (NXB) (Updated 2007 Dec 27)
- Current reproducibility of the PIN NXB is +/-3.2% (1 sigma) in (15-40 keV) (see Suzaku Memo 2007-09). The effect of this should be taken into account in the data analysis. The Technical Description for proposers contains a recipe for how one might do so.
- As to the GSO background, a similar description will be prepared after the release of the V2 NXB files.
- Cosmic X-ray background (CXB) in HXD data
- The background files provided by the team only accounts for the NXB component. Whereas the cosmic background makes a very small contribution to the GSO data, it is not negligible for PIN data. We have provided a recipe for including the CXB in the data analysis.
2. Software Issues
- XIS: arf generation
- The software to generate ancilary response files (ARFs) for XIS is based on the ray-tracing software. We provide hints on how to speed up ARF generation.
- We provide a simple script, xisresp which runs xisrmfgen and xissimarfgen for point source cases without the users having to know the details of these tools. (xisresp pha_file_name fast/medium/slow reg_file_name extended? echo?) (A new version, with minor updates, of xisresp was released on 2007 Dec 27). Note added on 2008 March 21: also note that xisresp users should use the new version of addascaspec that can handle a situation in which only the .rsp files exist.
- XIS: rmf generation
- While the process of generating XIS rmf is fast, there are tricks one can use in this stage, or immediately thereafter, to speed up the spectral fit.
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