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Filtering HRC Data



May 2002: An error in some pipeline reprocessing of HRC-S/NONE data has been identified. Only level 2 files processed before before July 2001 are affected. Update: As of 19 August 2002, all affected data have been reprocessed.


Data from the HRC go through several levels of processing. In level 1 processing, the results of filters evaluated on orbit and tests performed during automatic processing are recorded in a status flag for each event. The flag is 32 bits long, with each bit representing the result of a test. Definitions for each status bit can be found here. In level 2 processing, this status flag is used to filter out "bad" events. Here are the default status flags used in standard processing:

HRC-I: status=xxxxxx00xxxx0xxx00000000x0000000
HRC-S: status=xxxxxx00xxxx0xxx0000x000x00000xx

Some of the HRC filtering tests require that coefficients be supplied to set limits on acceptable events. The coefficients currently in use by Chandra automatic data processing can be found here.

In addition to filtering on the status flag, event lists are also filtered on the good time intervals (GTIs), and, for HRC-S data, PHA=0:300.

The standard filtering done by pipeline processing software as described above is considered to be the optimal solution by the CXC calibration and HRC IPI teams. Custom filtering on status=0 is strongly discouraged.


Level 1

Like Level 2, But No H-test

Level 2

Level 1 No H-test Level 2


The quality of HRC data has evolved over time due to improvements of Calibration Database (CALDB) Products and the Standard Pipeline Processing. As an example of how the revisions have improved image quality, we display an original HRC-I observation of ArLac done in October 1999 along with three reprocessings, shown in chronological order from left to right. The top row shows the level 1 images, and the bottom row shows the level 2 images. Note the improvement of the filtered (i.e. level 2) images with time.

# 1 - Nov 99

# 2 - Aug 00

# 3 - Dec 00

# 4 - Apr 01

Level 1

Version 1, Level 1 Version 2, Level 1 Version 3, Level 1 Version 4, Level 1

Level 2

Version 1, Level 2 Version 2, Level 2 Version 3, Level 2 Version 4, Level 2

Note that the numbers (1-4) above the images indicate the number of times this observation has been reprocessed, not the pipeline or CALDB version numbers used in reprocessing. To determine the pipeline and CALDB versions used in processing your observation, look for the ASCDSVER and CALDBVER keywords in the header of the data file. Release notes for each pipeline revision are available grouped by instrument, so one can track processing changes affecting HRC data products. CALDB release notes are also available.


The HRC IPI Team has developed a software tool (revised Nov 2001), screen_evt1, to allow users to screen their own data manually. See "HRC Event Screening" for more information about the tool, including how to download and run the code.

Contact CXC Calibration (cxccal@cfa.harvard.edu)
for further information

Last modified: 09/27/12

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