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Last modified: 24 February 2012


CalDB 4.4.8 Public Release Notes

Public Release Date: 23 FEB 2012

SDP Installation Date: 2012-02-17T12:30:00 (UTC)


CalDB 4.4.8 is an upgrade to the Chandra CalDB, which includes the following items:

  • ACIS T_GAIN Epoch 48

For the CIAO 4.4 / CalDB 4.4.8 release notes see How CalDB 4.4.8 Affects Your Analysis.


A. ACIS T_GAIN Epoch 48

Location: $CALDB/data/chandra/acis/t_gain
Filename: acisD2011-08-01t_gainN0006.fits

The periodic ACIS T_GAIN correction upgrade for Nov 2011-Jan 2012 has been released. The corrections are at nominal/expected levels of less than 2% of the energy value. This upgrade as usual affects observation data taken over Epoch 48 and 47, and so would update PHAs for OBS_IDs taken since 01 AUG 2011. Users with such datasets are encouraged to revalidate their analysis results after reprocessing their data with the upgraded CalDB files. Also, REPRO 4 will be reprocessing those data to update the archive essentially immediately, upon installation in the Standard Processing CalDB. For specific details of the new calibrations in this release, see the technical details section below.

See the ACIS Time-dependent Gain why page for more information.


DS and CIAO level 1 (re)processing tool acis_process_events.

Also: CIAO reprocessing script chandra_repro for ACIS data with DATE-OBS after (UTC) 2011-02-01T00:00:00.


Reprocessing Data to Create a New L2 Events File


A. ACIS T_GAIN Epoch 48

The ACIS time-dependent gain corrections (T_GAIN) have recently been updated for current changes from the previous T_GAIN epoch, specifically Epoch 48, which was Nov 2011 through Jan 2012. With the addition of these new corrections, derived from ACIS External Cal Source (ECS) data taken during radiation zone passes, the CalDB files extending from Aug 2011 through Oct 2011 (i.e. Epoch 47) have been finalized, and new non-interpolating T_GAIN files are now implemented for Epoch 48.

The magnitudes (in eV) of the new gain corrections, versus photon energy, are given in Figs. 1-3 below. The corrections are of the usual order in magnitude, specifically less than 2.0% of the photon energy value. Fig. 1 below gives the corrections for the ACIS-I aimpoint on chip ACIS-3, for the CTI-corrected case, which is the only one applicable to FI chips. Figure 2 gives the corrections for the ACIS-S aimpoint on ACIS-7, for the case where the BI chips are CTI-corrected. Finally Fig. 3 gives the corrections for ACIS-7 for NON-CTI-corrected BI chips. These would be relevant to GRADED DATAMODE observations with ACIS-S, for example.

Fig. 1: ACIS-I3 aimpoint T_GAIN corrections in eV versus photon energy.

Fig. 2: ACIS-S3 CTI-corrected aimpoint T_GAIN corrections in eV versus photon energy.

Fig. 3: ACIS-S3 non-CTI-corrected aimpoint T_GAIN corrections in eV versus photon energy.