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CalDB PUBLIC Release Notes
Effective Date: (UTC) 2008-03-24T16:00:00
Public Release Date: 31 March 2008
Version: 3.4.3
Release Type: SDP + PUBLIC

I. Introduction

CalDB 3.4.3 includes two T_GAIN upgrades. The first is for the usual current epoch update to Epoch 32 (Nov 07 through Jan 08), and the second part is the -110C upgrade to include a single T_gain file for 16 Sep 1999 effective through 28 Jan 2000. This latter includes TGAIN corrections ONLY for ACIS-S1 and -S3, and requires an upgrade to the S1 and S3 GAIN file as well. There is a particular advantage here for these two chips, because users may now reprocess their own -110C ACIS data, and use mkacisrmf for S3 and S1 RMFs. Also, for gratings observations, they get the new improved S1 GAIN function we
introduced for the -120C data with CalDB 3.3.0.

II. Summary of Changes

A. ACIS -120C T_GAIN Epoch 32

LOCATION: $CALDB/data/chandra/acis/bcf/t_gain/
FILENAMES: acisD2007-08-01t_gainN0005.fits (A-P-E "apply_cti=no")
        acisD2007-08-01t_gainN0006.fits (A-P-E "apply_cti=yes")
        acisD2007-11-01t_gainN0002.fits (flat, A-P-E "apply_cti=no")
        acisD2007-11-01t_gain_biN0002.fits (flat, A-P-E "apply_cti=yes")

Epoch 32 includes the 01 Nov 2007-31 Jan 2008 period. The T_GAIN interpolation files effective for 2007-08-01 include both Epochs 31 and 32. The new files effective on 2007-11-01 are non-interpolating or "flat" files including only Epoch 32. The four datasets follow the current convention for T_GAIN upgrades, in that the first and third files include data for S1 and S3 (the BI chips) that are NOT CTI corrected. The second and fourth files have CTI-corrected BI chip data.
For the FI data, the CTI correction is always applied, as no calibration for T_GAIN exists for the FI non-CTI case.

Pipes/Tools affected:
SDP/CIAO ACIS L1 processing tool "acis_process_events"
(ACIS data at FP_TEMP=-120C, DATE_OBS=2007-08-01T00:00:00 or later)

Threads affected:
"Reprocessing Data to Create a New Level=2 Event File
"
http://cxc.cfa.harvard.edu/ciao/threads/createL2/

See also the CIAO 4.0 release notes at:
http://cxc.cfa.harvard.edu/ciao/releasenotes/ciao_4.0_release.html#HowCALDB3.4.3AffectsYourAnalysis

B. ACIS T_GAIN -110C (16 Sep 1999 through 28 Jan 2000 *PLUS* Summer 2000 -110C CAL ObsIDs) and associated GAIN file

LOCATION: $CALDB/data/chandra/acis/bcf/t_gain/
FILENAME:       acisD1999-09-16t_gainN0005.fits

LOCATION: $CALDB/data/chandra/acis/bcf/gain/
FILENAME:       acisD1999-09-16gainN0006.fits

Pipes/Tools affected:
SDP/CIAO ACIS L1 processing tool "acis_process_events"
(ACIS data at FP_TEMP=-110C, DATE_OBS=1999-09-16T00:00:00 through 2000-01-29T20:00:00;
Also, Calibration Observations taken on 2000-07-03, 2000-07-05, and 2000-08-11 with FP_TEMP at -110C)

Threads affected:
"Reprocessing Data to Create a New Level=2 Event File
"
http://cxc.cfa.harvard.edu/ciao/threads/createL2/

See also the CIAO 4.0 release notes at:
http://cxc.cfa.harvard.edu/ciao/releasenotes/ciao_4.0_release.html#HowCALDB3.4.3AffectsYourAnalysis


III. Technical Details

A. ACIS Epoch 32 T_GAIN files

The new -120C T_GAIN data were derived from ACIS External Calibration Source (ECS) data taken during radiation zone passes during Nov 2007- Jan 2008. Here are the plotted corrections, showing the changes from the previous files and the new ones, for the aimpoint of ACIS-I3 (Figure 1).


Figure 1: A comparison of old and new T_GAIN corrections for the CTI-corrected FI chip I3 at the aimpoint. There is not much of change with the new files.


Likewise, below is the comparison between old and new T_GAIN data for the aimpoint of ACIS-S3, with the BI chip CTI correctors applied.


Figure 2: A comparison of old and new T_GAIN corrections for the CTI-corrected BI chip ACIS-S3 at the aimpoint. The changes here are minor as well, though a bit larger than the other two illustrated cases.


Now consider the non-CTI corrected case for ACIS-S3, applied to data for which the CTI correction is unavailable.

Figure 3: A comparison of old and new T_GAIN corrections for the CTI-corrected BI chip ACIS-S3 at the aimpoint. The changes here are minor as well.


Hence the new Epoch 32 T_GAIN corrections are basically necessary for optimal application of the time-dependent gains for the most recent Chandra ACIS data. Hence the continued need for our period upgrades to these data.


B. ACIS Epoch 0 (-110C, Sep 1999-Jan 2000) T_GAIN and GAIN files

Below is an illustration of the time-dependent correction to be applied to all -110C data taken between TT=1999-09-16T00:00:00 and 2000-01-29T20:00:00 at the aimpoint of ACIS-S3 (a BI chip). See figure 4. In fact, we will apply the same correction for all of these data, because it is meaningless to interpolate them with -120C data. The sense of the correction is the opposite for the -120C T_GAINs illustrated.


Figure 4: The T_GAIN corrections for -110C ACIS-S3 data at the aimpoint, compared with Epochs 1-4 -120C data. Note that the fix is in the opposite sense, i.e., that the correction in the energies is NEGATIVE for the -110C cases.


We also illustrate the effect for the midpoint of Chip S1 (ACIS-5). A very similar effect is seen, though the degree of change is somewhat larger for S1 than for S3 above.


Figure 5: The T_GAIN corrections for -110C ACIS-S1 data at the MIDpoint, compared with Epochs 1-4 -120C data. Here, too, the fix is in the opposite sense, i.e., that the correction in the energies is NEGATIVE for the -110C cases.


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