Last modified: December 2022

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AHELP for CIAO 4.16


Context: Tools::Utilities


Update file header with various keywords to match latest archive processing


Most data in the Chandra archive was reprocessed starting in January 2012 -- an effort to bring uniformity to the calibrations and data products. The internal designation was known as Repro-4. All but the first few months of data in the mission were included in this bulk processing. The ASCDSVER keyword will be '8.4.2' or higher for data that has been through repro-4. In addition to capturing the latest standard calibrations, there were several calibration improvements to astrometry and absolute timing. At the same time, two sets of keywords were added to the Chandra event files and derived products that make data analysis easier and more self-contained (ie requiring fewer auxiliary files).

For ACIS and HRC, three new keywords were added to capture the mean SIM offsets during an observation: DY_AVG, DZ_AVG, and DTH_AVG. These numbers are needed by tools like dmcoords, mkacisrmf, and mkwarf to correctly map detector coordinates back to the location on the instruments. Previously each tool used the information in the asolfile parameter to compute the mean value, every time the tool was run. With the mean values now simply encoded as header keywords, the tools can run more efficiently.

For ACIS, the information in the Level 0 parameter block file, pbk0, needed to compute the dead area calibration was also added to the event file headers. The new keywords include: SUM_2X2, FEP_CCD, ORCMODE, and OCLKPAIR. This information together with some existing keywords, is used by ARF and Exposure map tools when creating response.

The r4_header_update script will examine the header of the infile, determine which of the above keywords are missing, and will add them to the header.


Example 1

unix% dmkeypar my_old_evt.fits ASCDSVER echo+
unix% r4_header_update my_old_evt.fits
unix% dmkeypar my_old_evt.fits FEP_CCD echo+

This example shows and older version of an event file created with ASCDSVER=7.6.8. This file will not have the keywords necessary to run all CIAO 4.6 tasks.

The script will attempt to locate the auxiliary files it needs, the parameter block and aspect solution files. The file is updated in place.

Example 2

unix% r4_header_update my_old_evt.fits pkb=orig_pbk0.fits

If data are very old, then the information relating an event file to the parameter block and aspect solution may not be available in the event file header. In that case users will need to specify the auxiliary files explicitly.


There are no known bugs for this tool.