Things to Watch Out For
Last Updated Apr 26, 2016
This page contains the brief summaries of important issues that all Suzaku users should be aware of. It will be updated frequently to reflect our latest understanding of real and potential issues in Suzaku data analysis.
1. Calibration Issues
ISAS maintains the calibration status and caveats pages.
In addition, we note the following items:
- PIN NXB files for observations since 2012 August (2014 Jun 9)
- The HXD team has produced a new version of PIN "tuned" non X-ray background (NXB) files for data taken during or after 2012 August. This is because the accuracy of the version 2.0 tuned NXB has gradually deteriorated for these recent observations, underestimating the true background by 3-4% in 2013 December. For observations up to 2012 July, users should continue to use version 2.0 NXB files (in pinnxb_ver2.0_tuned directory, with METHODV keyword value of 2.0ver0804); for observations since 2012 August, users should use the files in pinnxb_ver2.2_tuned (with METHODV value of 2.2ver1403).
- Due to a change in operational parameters, PIN quick background files for observations between 2012 August and 2013 September were either not produced, or produced with errors (with 0 rows of good-time intervals). Users should only use the tuned NXB files for these observations. The HXD team plans to re-start generations of quick background files for observations since 2013 October, although this has been delayed due to technical issues.
- Effects of increasing low-level flickering pixels in estimating the XIS NXB
(Updated on 2016 Apr 26)
- The XIS team recommends a new recipe for weak, low surface brightness sources observed during the latter phases of the mission.
- The standard method to remove flickering pixels is statistical in nature: therefore, the longer the exposure, the activity level at which flickering pixels can be identified and removed becomes lower. Late in the mission, the number of such pixels increased to the point that the different efficiency of flickering pixel removal for the individual observations and the NXB background data base became noticeable.
- NXB database in the 2013-01-10 release of the XIS CALDB (Updated 2013 Mar 20)
- There was a problem in this version of the NXB database (files ae_xi?_nxb*_20121201.fits), such that xisnxbgen will produce a background map for the 1/4 window region only, regardless of the option used for your observation.
- The XIS CALDB has since been updated. The 2013-03-05 release (files ae_xi?_nxb*_20130228.fits) corrects the above problem.
- See this ISAS page for the details.
- Updated gain history file for HXD/GSO (2011 Sep 19)
- The HXD team has released an updated gain history file for the GSO that reduces the gain fluctuation for data taken since 2010 March (see the release note for further details). Affected users should reprocess their data.
- The corresponding GSO NXB files will be delivered soon.
- New gain calibration of HXD/GSO (Updated on 2010 Aug 20)
- This extends the usable energy range down to 50 keV.
- Users must choose a consistent set of software, calibration files, background files, and response files. See explanation (updated on 2010 Aug 20). A set of emprical arf files for the new gain calibration are also available (2010 Aug 20).
- HXD/PIN - XIS Cross Normalization (Updated 2008 Jul 31)
- With the 2008-07-09 release of CALDB used with Version 2 data,
the normalization of PIN data relative to XIS0 data is 1.16 for
observations of the Crab at the XIS nominal position, and 1.18
for those at the HXD nominal position (uncertainty is ~0.015). See
Memo 2008-06 for details.
With older calibrations, 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.
- With the 2008-07-09 release of CALDB used with Version 2 data, the normalization of PIN data relative to XIS0 data is 1.16 for observations of the Crab at the XIS nominal position, and 1.18 for those at the HXD nominal position (uncertainty is ~0.015). See Suzaku Memo 2008-06 for details.
- PIN - GSO Cross Normalization (Posted on 2008 Jun 27)
- With the current calibration, in the 2007 March 20 observation
of the Crab at the HXD nominal position, there is a cross-normalization
problem at the 20% level (1.0:0.80, PIN:GSO) and ~10% residuals in
the GSO data.
The HXD team is working on resolving this issue. In the mean time, empirical arfs can be used to reduce both problems significantly.
- With the current calibration, in the 2007 March 20 observation of the Crab at the HXD nominal position, there is a cross-normalization problem at the 20% level (1.0:0.80, PIN:GSO) and ~10% residuals in the GSO data.
- XIS: Increased non
X-ray Background for XIS1 with CI=6 keV
(2012 Mar 28)
- XIS: Energy scale and resolution calibration as verified using the 55Fe calibration soruce
- SCI data processed using V184.108.40.206 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) (Updated 2008 Oct 22): There was an offset in the 2x2 mode energy scale relative to the 3x3/5x5 modes. This is believed fixed with the release of ae_xiN_makepi_20080825.fits files in 2008 September. Users should apply the new calibration using the same procedure as for SCI-on data processed with V220.127.116.11 or earlier.
- 2x2 mode (SCI-on): (Added on 2008 Oct 22): The energy scale for 2x2 mode with charge injection is expected to be similar to those of the 3x3/5x5 modes. However, this expectation has not yet been verified with actual calibration. Users of 2x2 mode data with SCI should carefully check for gain discrepancies.
- Window mode data: (Added on 2009 Jun 4): The energy scale calibration for XIS data with the 1/4 and 1/8 window mode options has been updated. Users analyzing window mode data should update the energy scale using xispi in Version 12 of Suzaku FTOOLS.
- 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.
- With the release of XRT CALDB 20080709, regions as small as 1 arcmin radius can be used without noticeably affecting the flux calibration (Posted 2009 Dec 4)
- 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: New contamination model (Updated 2012 Oct 15)
- The 20120902 version of XIS CALDB includes updated calibration files (dated 20120719) for the contaminantion build-up. See this page for further details.
- Note that the contamination model formula, used in xissimarfgen and xiscontamicalc, was updated in Version 18 of Suzaku FTOOLS. Users of older versions of FTOOLS (which assumed a fixed contaminant composition, with C/O=6) cannot take advantage of the newer calibration files.
- XIS: Calibration around the Si K edge (Updated on 2013 Mar 5)
- There has been a calibration problem in the 1.6-2.0 keV region at the +/-10% level, which is noticeable in bright source data. See details.
- The XIS team has released a new set of quantum efficiency files in 2012 June, which are believed to improve the calibration in this energy range.
- They have also updated the response generator, xisrmfgen, released in 2012 December, which is believed to improve the calibration at these energies for the BI chip. This is now also described on the same page mentioned above.
- XIS: Problem in non X-ray background database for XIS1 without SCI (2008 Sep 15)
- The XIS team has discovered a problem in the latest NXB database for XIS1 for SCI-off observations (ae_xi1_nxbsciof_20071226.fits); the database includes data before the XIS1 door opened. Please refer to the detailed explanation on this ISAS page.
- XIS: Burst mode exposure time (2009 Dec 4)
- Until now, the good time interval (GTI) of the XIS event files did
not contain the detailed GTI information for burst mode data
(e.g., one line for each 2 second exposure separated by 8 seconds).
This led to inaccuracy in the exposure times after data screening
The XIS team has released a new version of xistime, with a new option "bstgti=yes," as part of Suzaku software V14 in HEASoft v6.8. This will produce the detailed GTIs. Note that the GTI extension may then contain a large number of rows, potentially causing problems in donw-stream software. Also note that this option works even when the data were taken without burst mode, but this is not recommended.
- Until now, the good time interval (GTI) of the XIS event files did not contain the detailed GTI information for burst mode data (e.g., one line for each 2 second exposure separated by 8 seconds). This led to inaccuracy in the exposure times after data screening and/or selection.
- Expanded Area of Charge Leakage on XIS0 (Updated 2015 May 21)
- Since some time between 2014-05-15 and 2014-06-02, the charge leakage area of XIS0 expanded. Starting on 2014-10-01, an expanded area discrimination area will be used for XIS0 data. See this page at ISAS for further details.
- The expansion of charge leakage area also led to a sudden change in the energy scale. The data should be (re)processed using makepi file dated 20141222 and rmf file should be generated using rmfparam file dated 20141224, both of which are included in CALDB release 2015-01-05 or later.
- To run aepipeline on data taken recently, it may be necessary to use the newest version of aexisconf.list (last updated: 2016 Mar 2). This will be included in a future release of Suzaku FTOOLS; in the mean time, users can download this file and install it in the refdata area of their FTOOLS installation.
- New OBF Holes in XIS1 and XIS3 (2013 Aug 16)
- A total of 10 new bright spots were found in the frame dump images of XIS1 and XIS3 in 2013, likely caused by small holes in the optical blocking filters. No effects on the X-ray data are expected in most cases. See Suzaku memo 2013-01 for further details.
- XIS1: Light Leak in a small area of XIS1 (2010 Jul 12)
- A small area of XIS1 has developed a light leak, presumably due to a micrometeorite hit. This is obvious in bright Earth data, but should not impact most observations of celestial X-ray sources. The XIS team is nevertheless investigating if there are any changes in calibration due to this. See Suzaku Memo 2010-03 for further details.
- Unlike the situation for XIS2 or XIS0, the full area of XIS1 continues to be available for X-ray observations.
- PIN responses by epoch (Revised 2009 Dec 4):
- 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.
- PIN epoch 6: In particular, HXD/PIN data taken since 2008 Oct 1 have been processed using an updated low energy threshold file. Users of these data should use an "epoch 6" PIN response file, but there is no need for reprocessing of PIN data because of this change.
- V2 PIN background files (Revised 2008 Jun 17)
- There are now two types of PIN non X-ray backgroun (NXB) files, "tuned" and "quick." The tuned model has an estimated 1-sigma systematic uncertainty of 1.3%, which is significantly better than for the quick model. Therefore, the tuned NXB files should be used whenever available.
- However, production of the tuned NXB files takes 1-2 months after the processing of observations. The quick NXB files can be produced with a much shorter delay of 1-2 weeks. Therefore, the HXD team will continue to produce NXB files using both methods.
- Dead-time correction is not necessary for the tuned or the quick NXB files. In this respect, the tuned NXB files differ from the V1.2 bgd_d NXB files, even though both are based on the same family of models.
- 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.
- 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
- Perl version mismatch (Added May 12, 2010):
The binary distribution of HEAsoft includes pre-compiled perl libraries.
For each operating system, they are created using a specific version of
perl. If a user's system has a different version, this can lead to
problems. The user needs to install the same version of perl as used
in building the HEAsoft binary, or build from source. See
the HEAsoft page on this issue
for further details, including a table of OS-perl version pairings.
- HXD: hxdpinxbpi in Suzaku
FTOOLS Version 14 (Added Feb 4, 2010):
- When pinnom_rsp=CALDB is specified, it failed to
select the PIN response file based on the pointing position
of the source (HXD nominal or XIS nominal) to be written in
the RESPFILE keyword of the output spectrum. The former was
automatically selected. Users analyzing observations at XIS
nominal pointing position using this would have obtained
an incorrect normalization.
This has been corrected in Suzaku FTOOLS Version 15, which is available as part of the HEAsoft V6.8 distribution as of January 29, 2010. Those who installed HEAsoft V6.8 between the original date of release (December 3, 2009) and January 29, 2010 can install a patch avaialble via the HEAsoft v6.8 bugs page.
- When pinnom_rsp=CALDB is specified, it failed to select the PIN response file based on the pointing position of the source (HXD nominal or XIS nominal) to be written in the RESPFILE keyword of the output spectrum. The former was automatically selected. Users analyzing observations at XIS nominal pointing position using this would have obtained an incorrect normalization.
- HXD: hxdtime and hxdpi on Fedora (Linux) machines
(Updated Nov 6, 2009):
- Mysterious memory faults seen in hxdtime and hxdpi, along with other (non-Suzaku) software, have been attributed to the early GCC 4.x compiler series (GCC 4.0.x, 4.1.x, shipped with operating systems such as Fedora 7, 8, 9). The software seems to behave properly when built with newer compilers (4.2.x, 4.3.x, 4.4.x) or older compilers (3.4.x).
- XIS: xisnxbgen for XIS1 data taken with CI = 6 keV (2012 Nov 29)
- Due to the current structure of the CALDB, xisnxbgen
is unable to pick the correct file automatically for XIS1 data taken
with CI = 6 keV. For such data, please explicitly specify the
nxbevent calibration file:
If you have a copy of the Suzaku CALDB locally installed, this file can be found in the CALDB data/suzaku/xis/bcf directory. If you are using the HEASARC version of the CALDB remotly, it is probably best to download this specific file from: ftp://legacy.gsfc.nasa.gov/caldb/data/suzaku/xis/bcf/
Read more about the NXB increase with CI=6 keV.
- Due to the current structure of the CALDB, xisnxbgen is unable to pick the correct file automatically for XIS1 data taken with CI = 6 keV. For such data, please explicitly specify the nxbevent calibration file:
- XIS: xissimarfgen and xiscontamicalc (2011 Jun 10)
- These tools in Version 17 or older are incompatible with the default contamination calibration files in the latest XIS CALDB (20110608). Users are strongly encouraged to obtain Version 18 of Suzaku FTOOLS, since they incorporate the new model of contaminant.
- XIS: xissim and xissimarfgen (Added Jul 31, 2008)
- The 2008-07-09 release of CALDB requires these two tools, both of which rely on the raytracing library, to be updated to those found in Version 8 or higher of Suzaku FTOOLS. The new software is backward compatible with older calibration files. However, older versions of software will not run with the latest CALDB.
- XIS: xispi with remote CALDB access (Updated Jul 31, 2008)
- The bug in xispi reported below has been fixed with the
Version 9 release of Suzaku FTOOLS.
The older version of xispi has a bug in the code that judges whether PARARELL_CTI parameters should be re-read from the calibration file, for observations with SCI. The bug makes xispi read the calibration file many times unnecessarily. While the results of the calculations are correct, there is a high overhead particularly with remote CALDB access.
- The bug in xispi reported below has been fixed with the Version 9 release of Suzaku FTOOLS.
- 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.
- Updated 2008 Jul 31: in the simple case (point source centered on the extraction region), it is simplest to generate the response when extracting the spectrum within xselect. Simply use the resp=yes option with the extract spectrum command. This will leave a combined .rsp file, having run both xisrmfgen and xissimarfgen.
- 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.
- addascaspec (Updated 2009 Dec 7)
- The new version of addascaspec released with HEASoft v6.8 corrects the buG contained in the previous version.
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