Notes on V2.0/2.1 processed XIS Data

2007-10-31 by the XIS team
Updated 2007-12-06

1. Changes from V1.x to V2.0/2.1

Major changes incorporated in v2.0/2.1 processing are described in the processing description page.

2. Data screening criteria used in ver2.0/2.1

The standard screening criteria used in the processing pipeline are listed here. Users can produce their own cleaned event files by applying a slightly modified set of criteria.

Frequently seen examples of frequently modified screening criteria are:

a. Weaker constraint on the DYE_ELV for the hard sources,
b. Application of one of the alternative criteria listed in Table 4 for extracting night/day-earth events.

Limitations of Calibrations

Now we know several limitations of calibration for the SCI-on normal mode data, as follows.

Energy Resolution

When we fit Mn Kalpha line taken around 2006 September using the current response (either using the files provided for AO-2 proposers, or generaing new ones using xisrmfgen), an additional line width of 30eV is foudn for both FI and BI data.

Energy Scale (CTI and Gain) for data processed with pipeline V2.1.6.15 and older

We have calibrated the energy scale of both FI and BI chips so that the center energy of the Mn Kalpha line is 5.895keV in 2006 September
For the FI chips, we have not tuned the energy dependence of the CTI, nor have we calibrated the gain at low energies. Thus, (a) the systematic uncertainty of the gain is 15eV at most for the Fe XXV Kalpha line, and (b) there may be a positional dependence of the gain in the low energy band^*.
The CTI calibration for the BI chip has not been carried out. Therefore, we cannot gurantee the accuracy of the gain except at the Mn Kalpha line
We have not yet implemented the time variability of the CTI for the FI or the BI chips. Hence, the gain of the Mn Kalpha line after 2006 September decreases with time. The rates of the energy shift are about 30eV/year for the FI chips and 50eV/year for the BI chip.

^*Note: We started the SCI to improve the CTI on 2006 September. Thus, the positional dependence of the gain due to the CTI was rather small at that time

It is believed that the calibration files used in processing pipeline v2.1.6.16 eliminates the above problems. Users can apply the new calibration to their data.

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This file was last modified on Thursday, 06-Dec-2007 11:48:10 EST