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Last modified: 9 April 2014


CalDB Public Release Notes

Public Release Date: 09 APR 2014

Not installed in SDP


CalDB is patch correction to the Chandra CalDB, and includes the following item only:

  • HRC-I BKGRND 2012, 2013 Validity Date Corrections

For the CIAO 4.6.1 / CalDB release notes see How CalDB Affects Your Analysis.


A. HRC-I BKGRND 2012, 2013 Validity Date Corrections

Location: $CALDB/data/chandra/hrc/bkgrnd/
Filenames: hrciD2012-01-01bkgrndN0002.fits

The CalDB Manager has found an error in the index listings of the 2012 and 2013 HRC-I BKGRND files that were released in CalDB 4.6.1 on 26 March 2014. While the error does NOT affect Standard Data Processing (SDP) in any way, it does affect those with HRC-I data who want to use the CIAO contributed script "fluximage" (or a manual procedure similar to that) with observations taken since 2012-01-01T00:00:00 UTC. The error occurs because the Calibration Validity Start Date (CVSD) and Calibration Validity End Date (CVED) values are reversed between two of the HRC-I BKGRND event files listed above.

The result is that the 2013 file above is selected for 2012 OBS_IDs, and the 2012 file is selected for 2013 and beyond OBS_IDs.

The fix is to correct the CVSD0001 and CVED0001 values in the two named files, and then rebuild the HRC branch index file. This has been done and verified CalDB as detailed in the technical details section below.


For OBS_IDs taken since 2012-01-01T00:00:00 UTC only:


HRC-I Exposure Map and Exposure-corrected Image


A. HRC-I BKGRND 2012, 2013 Validity Date Corrections

The problem with the HRC branch index and the 2012 and 2013 HRC-I BKGRND event lists occurs when one is using the CIAO 4.6.1 script hrc_bkgrnd_lookup or the contributed script fluximage, for any OBS_ID with DATE-OBS after 2012-01-01T00:00:00 (UTC). This can be illustrated with three OBS_IDs in particular from calendar years 2012, 2013, and 2014. Note that the HRC-I BKGRND event lists are valid one full calendar year beginning with the date in their respective filenames. The table below gives the OBS_IDs, their starting dates and times (DATE-OBS), and the files selected by hrc_bkgrnd_lookup with CalDB 4.6.1 (third column) and CalDB (fourth column).

HRC-I BKGRND event list
CalDB 4.6.1
HRC-I BKGRND event list
CalDB patch
14262 2012-08-10T20:40:36 hrciD2013-01-01bkgrndN0002.fits hrciD2012-01-01bkgrndN0002.fits
14916 2013-10-03T22:51:57 hrciD2012-01-01bkgrndN0002.fits hrciD2013-01-01bkgrndN0002.fits
15473 2014-01-14T01:20:28 hrciD2012-01-01bkgrndN0002.fits hrciD2013-01-01bkgrndN0002.fits

As shown in the table (third column), the wrong BKGRND event list is selected for CalDB 4.6.1 in all three cases. However, as given in the fourth column above, the correct file is selected in all three cases with the corrected index in CalDB Hence the CalDB patch upgrade fixes the problem.