Energy Scale of XIS Taken with a Window Option
2009-06-04 by the XIS team and the GOF
The XIS team has updated the energy scale assignment tool, xispi,
in Version 12 of
This revision incorporates an update of the CTI correction formula
that is important for users analyzing XIS data taken with a (1/4 or 1/8)
window option. All such users should install Version 12 of Suzaku
FTOOLS, and reprocess the data with the new version of xispi.
Although it is a good practice to always use the latest calibration
files through the Suzaku
CALDB, this update of xispi is independent of CALDB update
and is not tied to specific versions of calibration files.
Explanation of the Change
We have noticed a discrepancy in the energy scale of window option
data, compared with the full window data. For observations with SCI
off, the 1/4 window mode data are offset by about
40 eV at 6 keV for the FI CCD, and 60 eV for the BI CCD (=XIS1).
This discrepancy has been resolved by considering the different
types of charge transfer. Radiation damage has created charge traps,
leading to charge transfer inefficiency (CTI), reducing the pulse
height that is out for the same amount of charge originally created
by an X-ray photon. However, CTI per transfer is different between
fast charge transfers and slow charge transfers. Because the numbers
of fast and slow charge transfers are different between the full window
mode and the window mode, this leads to differences in energy scales.
The new xispi incorporates a new formula that takes the
two types of charge transfer fully into account. With this,
the energy scale of the FI and BI data in 1/4 window mode with SCI-off
are in agreement to within +/-20 eV at 6 keV with that of the full window
Although this is also believed to improve the agreement between
the full window and the 1/4 window modes for SCI-on data, a detailed
evaluation has not yet been completed.
ISAS/JAXA Department of High Energy Astrophysics
Last Modified: Wednesday, 10-Jun-2009 14:03:31 JST