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CalDB Release Notes
Effective Date: 09 August 2006
Version: 3.2.3
Release Type: SDP + PUBLIC


CalDB 3.2.3 is a patch upgrade to version 3.2.2, which includes two new files affecting only the HRC-I configuration, and both of which are used only by the pipeline/CIAO tool "hrc_process_events". One is an upgrade to the "degap" correction data table (GAPLOOKUP), and the other is a correction to the HRC-I gain map (GMAP) applicable to observations taken before UTC=1999-10-04T12:00:00, i.e. applicable only to the first two months of the Chandra mission.

CalDB 3.2.3 will be installed in Standard Data Processing, and released to the public as a cumulative upgrade to any and all preceding versions back to CalDB 3.0.0 (released in December 2004).


A. HRC-I GAPLOOKUP Table version N0002

This new GAPLOOKUP table will improve the encircled energy fraction modestly but significantly for any on-(optical-)axis point sources. As such it represents the latest and best degap correction data available for the Chandra HRC-I. The data were derived from numerous Capella imaging observations taken throughout the mission, and verified against point sources such as AR Lac, 3C273, and Cen A.

An illustration of the improvement in the encircled energy fraction versus radius from the source position is given in Fig. 1 below:

HRC-I encircled energy fraction OBSID 1385 Ar Lac
Fig. 1: Illustration of the encircled energy (COUNTS) fraction versus radius for the N0001 (black curve) versus the new N0002 (red curve) HRC-I GAPLOOKUP tables.

Pipes/Threads affected:
SDP HRC L1/CIAO tool hrc_process_events

Create a New Level=2 Event File

HRC-I Degap Correction

B. HRC-I 1998-10-30 gain map (GMAP) version N0002 (correction)
Location: $CALDB/data/chandra/hrc/bcf/gain/
Filename: hrciD1998-10-30gainN0002.fits

The HRC team has informed us that the early mission gain map for HRC-I, released with CalDB 3.2.0 in November 2005, is in error. The image in the file hrciD1998-10-30gainN0001.fits is shifted in the horizontal (U) axis, and will generate errors in the calculated PI's in hrc_process_events. The HRC team has provided an correction to this file for immediate testing, inspection and release. The CalDB manager has complied, releasing the N0002 version of the same CalDB file type.

NOTE: This gain map is applicable only to HRC-I observations taken within the first two months of the mission, specifically before UTC 1999-10-04T12:00:00. Only the PI values are adversely affected by the errant GMAP file. If you have reprocessed observations within this period since November 2005, in order to use the PI information included for quantile color-color mapping, you will need to repeat that reprocessing with the corrected GMAP in CalDB 3.2.3.

Pipes/Threads affected:
SDP HRC L1/CIAO tool hrc_process_events

Create a New Level=2 Event File


A. HRC-I GAPLOOKUP Table version N0002

The derivation of the new GAPLOOKUP table is presented in the memorandum "HRC-I Degap Lookup from Capella Data" http://hea-www.harvard.edu/~juda/memos/hrci_degap_lookup/capella/degap/degap_lookup.html. It was developed using twenty Capella observations taken during the Chandra Cycle 7 observation period. The method that was to be used was presented in an earlier memorandum, "HRC-I Degap Lookup Table"
at http://hea-www.harvard.edu/~juda/memos/hrci_degap_lookup/index.html. Fig. 1 above illustrates the improvement made using version N0002 versus version N0001 of the GAPLOOKUP table for HRC-I.
B. HRC-I 1998-10-30 gain map (GMAP) version N0002
We have been alerted of an errant HRC-I Gain Map (GMAP) installed and released in CalDB 3.2.0 in November 2005 has an errant shift in it which will adversely affect PI's calculated from it. That GMAP (filename: hrciD1998-10-30gainN0001.fits) contains the following image:

HRC-I errange GMAP N0001 (early in mission)
Fig. 2: The shifted GMAP image in the horizontal (U) axis direction contained in the N0001 GMAP file, which is being replaced. The dark maroon vertical stripe on the right side of the image is a region of zero image values, which would corrupt the calculated PI values generated therefrom. The scale is linear, with minimum image value of "0" and maximum of "4.5748"

The new map, minus the shift, is shown in Fig. 3 below:
HRC-I GMAP N0002 (corrected)
Fig. 3: The image from the corrected GMAP version N0002. The image minimum value is now "0.8508" and the max is the same as the above, "4.5748".

The image value is used pixel-for-pixel to convert PHA values in the level 1 events file EVENTS table into the PI (pulse-invariant) values, via the formula PI = PHA * GMAP. Hence having zero values in the GMAP, as in Fig. 2 above, would produce PI's of "0" over a portion of the data, which would sabotage the use of the quantile color-color mapping recommended for the derivation of hardness ratio estimates for those events.

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