CalDB PUBLIC Release Notes

Effective Date: (UTC) 2008-06-16T16:30:00
SDP Installation Date: (UTC) 2008-06-16T17:00:00

Public Release Date: 23 June 2008

Version: 3.4.5

Release Type: SDP + PUBLIC

I. Introduction

CalDB 3.4.5 includes only the ACIS T_GAIN Epoch 33 upgrades. No other changes are included.

II. Summary of Changes

ACIS -120C T_GAIN Epoch 33

LOCATION: $CALDB/data/chandra/acis/bcf/t_gain/
FILENAMES: acisD2007-11-01t_gainN0005.fits (A-P-E "apply_cti=no")
        acisD2007-11-01t_gainN0006.fits (A-P-E "apply_cti=yes")
        acisD2008-02-01t_gainN0002.fits (flat, A-P-E "apply_cti=no")
        acisD2008-02-01t_gain_biN0002.fits (flat, A-P-E "apply_cti=yes")

Epoch 33 covers the 01 Feb through 30 April 2008 period. The T_GAIN interpolation files effective for 2007-11-01 include both Epochs 32 and 33. The new files effective on 2008-02-01 are non-interpolating or "flat" files including only Epoch 33. 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"

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

User Documentation:
"How CalDB 3.4.5 Affects Your Analysis"
http://cxc.cfa.harvard.edu/ciao/releasenotes/ciao_4.0_release.html#HowCALDB3.4.5AffectsYourAnalysis
Why Topic: "ACIS Time-dependent Gain Correction (T_GAIN)"
http://cxc.harvard.edu/ciao4.0/why/acistgain.html

III. Technical Details

A. ACIS Epoch 33 T_GAIN files

The new -120C T_GAIN data were derived from ACIS External Calibration Source (ECS) data taken during radiation zone passes during Feb - April 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 33 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.