Updated Gain Calibration for SCI-on Data

Nov 15, 2007

The XIS team has updated the CALDB files ae_xiN_makepi_20071031.fits, which are used by xispi which calculates the PI values. The files include time-dependent CTI paramters for the SCI-on data, and thus eneble us to correct the decrease in the gain after 2006 September.

The processed pipeline version 2.1.6.16 is the first version to use these revised "makepie" files. Users should check the pipeline version used for processing their data by reading the PROCVER keyword in their data files.

Version 2 processing pipeline used older versions of the "makepi" files up to V2.1.5.15. For SCI-on XIS data taken 2006 September, this resulted in the gain of Mn K alpha calibration line decreasing at a rate of about 30 eV/year in the FI chips (read this page for further details).

Users can reprocess their own SCI-on data (processing version 2.x) as follows.

Install the latest version of CALDB (or download the contents) from the CALDB page at GSFC or from the CALDB page at ISAS.
Run xispi to recalculate the PI values. Note that the XIS HK files are in the xis/hk subdirectory.
```
example% xispi infile=ae101005070xi0_0_3x3n066z_uf.evt.gz \
               outfile=ae101005070xi0_0_3x3n066z_uf_new.evt \
               hkfile=../hk/ae101005070xi0_0.hk.gz
```
Hidden paramter, makepifile should be set to CALDB if accessing the latest CALDB, or explicitly specify ae_xi0_makepi_20071031.fits.

Notes:

We recommend Suzaku FTOOLS Version 6 (HEAsoft v6.3 or later).
Since the grade determination is based on the CTI-corrected pulse height values in the PHAS column, users should reprocess starting with the unfiltered event files. The standard screening criteria are summarized here.
Currently, xselect does not treat the PHAS column correctly when merging 3x3 and 5x5 files. They should be reprocessed separately.

Added on Dec 6, 2007: Once all unfiltered event files are reprocessed with xispi, they must be screened. For convenience, we provide an xselect script xisrepro.xco (NB this script assumes that you are running xselect in a subdirectory of xis), which references event selection criterion file xis_event.sel and the standard good-time interval selection file xis_mkf.sel. Users should download these three files into the current working directory, make sure the filter file (.mkf in ../../auxil directory) is uncompressed, read in the updated unscreened event file(s) into xselect, then type

xsel > @xisrepro

This will cause xselect to apply the event selection, remove flickering pixels (using cleansis), and apply the standard GTI selection. If desired, users can edit xis_mkf.sel to adjust the screening criteria. Xselect will pause and ask the users to give the output (screened) event file name.

We have checked that the time variability of the energy gain is <0.2% for the Mn K alpha line for the reprocessed data up to 2007 February. Note that the CTI parameters after 2007 May are extrapolated. Thus, we cannot gurantee the same level of accuracy for more recent observations. The CTI parameters will be updated in future releases of the CALDB.

Energy Scale for XIS2

The gain parameters have been updated for all XIS units, including XIS2. However, we have few SCI-on data for XIS2 because of the anomaly. Please note that the gain uncertainty for XIS2 is probably large below the Si edge.

If you have any questions concerning Suzaku, visit the Feedback form.

This file was last modified on Thursday, 17-Jan-2008 16:15:58 EST