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HRC Degap Corrections

For the latest information on the degap files, see the HRC Calibration page at cxc.harvard.edu/cal/Hrc/detailed_info.html#degap

As of Apr 2006, the degap products in the CALDB were:

A description of the polynomial degap solution, as was used prior to CALDB 3.0.4, can be found on the old degap page.

Summary of the new (v2) HRC-S degap
We have derived corrections to the wavelength scale based on analysis of sources with strong line emission (Chung et al. 2005). This was first made available via a Perl script corrlam and has now been incorporated directly into the degap solution (Kashyap et al. 2005). The new degap, which is the polynomial solution modified by corrections derived from line-emission data, is available from CALDB 3.2.0 onwards in the file


This solution improves the performance of the LETGS significantly, but does not account fully for all the systematic errors in the dispersion relation. The rms deviation of the wavelength differences drop from 0.014 (0.010 over just the central plate) prior to the correction, to 0.010 (0.006 over the central plate).

Further reading:

HRC Degap Coefficients

The software for generating the degap coefficients has been developed by the HRC IPI team as part of their "unix" tools. In addition, Mike Juda has made modifications to the software (for example, to derive coefficients from 1 long HRC-S projection file and generate 1 complete HRC-S degap table, instead of 1 table for each segment).

Version 2 for the I and version 3 for the S did not run with the software available from this site. These versions have been replaced with versions 2.1 and 3.1 respectively. They derive from the same data, but are in standard CXC format.

Version 3 for the I was developed after applying the de-ringing software developed by the IPI team to the sub-assembly flat field data.

For instructions on making degap corrections, please see the appropriate CIAO analysis thread. There is one for the HRC-I and another for the HRC-S.

Information about recently addressed LETG and HRC-S data processing problems is available through the LETG Observer Information page.

[**NOTE: to download files, hold down "Shift" key and click on the link**]


HRC-I HRC-S notes
best-fit coefficients
FITS Format (for ASCDS)


Comments to cxccal@cfa.harvard.edu

Last modified: 06/11/18

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