CalDB PUBLIC Release Notes

Effective Date: (UTC) 2009-09-16T13:45:00
SDP Installation Date:2009-09-16T13:45:00

Public Release Date: 17 September 2009

Version: 4.1.4

Release Type: PUBLIC

I. Introduction

CaldB 4.1.4 is an upgrade to all previous CalDB4 versions 4.1.x. It includes the following upgrades:

ACIS T_GAIN Epoch 38 (01 May through 30 July 2009)
Header changes for ACIS -90C Level 1 calibration files applicable to engineering data from July-Aug 1999.
Addition of new ACIS -120C Level 1 calibration files applicable to CTI calibration data only.

Only the new ACIS T_GAIN affects current science observations and processing in any immediate way. See the technical details (Section III below) for information regarding effects of these new calibrations on analysis.

User Documentation:
"How CalDB 4.1.4 Affects Your Analysis"
http://cxc.harvard.edu/ciao/releasenotes/ciao_4.1.2_release.html#HowCALDB4.1.4AffectsYourAnalysis

II. Summary of Changes

A. ACIS T_GAIN Epoch 38

LOCATION: $CALDB/data/chandra/acis/t_gain/
FILENAMES: acisD2009-02-01t_gainN0005.fits
acisD2009-02-01t_gainN0006.fits
acisD2009-05-01t_gainN0002.fits

acisD2009-05-01t_gain_biN0002.fits

acisD2009-05-01t_gain_secN0002.fits

The Epoch 38 (May- Jul 2009) have now been released as indicated above; hence the Epoch 37 interpolations (the 2009-02-01 filenames above, applicable for observation dates Feb through May 2009) are now finalized. The previous epoch N0002 files have been demoted to "BAD" status, though they are still in the circulation with the CalDB, just in case they are needed for comparison to earlier analyses. See the Tech Details below for information on the degree of effect versus energy that the new corrections will have on your particular ACIS datasets. These new files will only affect data with DATE-OBS after 2009-02-01T00:00:00. All earlier data are unaffected by this change.

Users analyzing observations with DATE_OBS later than 2009-02-01 are encouraged to reprocess their Level 1 events data through Level 2, to verify whether or not their previous analysis results are at all affected by these new data. The plots in Tech Details section III.A give some a priory indications of how these data will affect them.

Pipes/Tools affected:
SDP/CIAO tool acis_process_events

Threads affected:
Any thread that employs acis_process_events with the parameter apply_tgain set to "yes", which is the default state. Specifically,
"Reprocessing to create a new (ACIS) L2 events file"
http://cxc.harvard.edu/ciao/threads/createL2/index.html#acis

B. ACIS -120C SECONDARY Level 1 calibration files

BRANCH: $CALDB/data/chandra/acis/
CODENAME: BADPIX
FILENAMES: acisD2000-11-28badpixN0005.fits

acisD2000-11-28badpix_secN0005.fits

CODENAME: CTI

FILENAMES: acisD2002-08-01ctiN0006.fits

acisD2002-08-01cti_secN0006.fits

CODENAME: DET_GAIN

FILENAME: acisD2000-01-29gainN0006.fits

acisD2000-01-29gain_cti_secN0006.fits

For the pre-existing files (the ones without “_sec” in their filenames, the only change is to add the boundary condition for OBS_MODE in the headers, set to allow OBS_MODEs POINTING, RASTER, SCAN, and SLEW, i.e., everything but SECONDARY. For the “_sec” files, the FP_TEMP boundary condition is extended to include all applicable ACIS FP_TEMPS (148.15-188.15 Kelvin), and OBS_MODE is limited to SECONDARY. Hence only the ACIS CTI ECS exposures taken during radiation zone passes on each orbit will use these datasets, unless some other SECONDARY mode observations are set up in the loads. This excludes the problem of occasional processing errors where a CTI check was done with FP_TEMP drifting high in the rad zone due to bright earth exposure on the ACIS passive radiator.

Pipes/Tools affected:
CIAO tool acis_process_events

Threads affected (for ACIS OBS_MODE=SECONDARY data only)
"Reprocessing to create a new (ACIS) L2 events file"
http://cxc.harvard.edu/ciao/threads/createL2/index.html#acis

C. ACIS -90C Level 1 calibrations affecting OAC (July-Aug 1999) ERs

BRANCH: $CALDB/data/chandra/acis/
CODENAME: BADPIX

FILENAME: acisD1999-07-22badpixN0005.fits

CODENAME: DET_GAIN

FILENAME: acisD1999-07-22gainN0002.fits

CODENAME: FEF_PHA

FILENAME: acisD1999-07-22fef_phaN0002.fits

CODENAME: OSIP

FILENAM: acisD1999-07-22osipN0004.fits

These changes affect reprocessing of ACIS data with the focal plane temperature set to either -90C or -120C during the Orbital Activation and Checkout (OAC) phase of the Chandra mission, during July and early August 1999. The alterations were made to the boundary conditions for FP_TEMP, to allow the two different temperature ranges (148.15-158.15 and 178.15-188.15 Kelvin) for the files above, as well as to reset the calibration validity end date (CVED0001) to the exact date (UTC) 1999-08-13T05:45:45, the same value as DATE-END for ER Obs_ID 62566, the final ER taken at -90C during OAC. These changes do not affect any science observations, as they affect data taken before the Chandra Sun Shade Door was opened.

Pipelines affected: ACIS L1 pipeline acis_process_events (gainfile only)

Currently the ACIS BADPIX files are not selected by FP_TEMP, but this may change in the future. FEF_PHA and OSIP files have had the same header changes for consistency and completeness in the CalDB.

III. Technical Details

A. ACIS T_GAIN Epoch 38

The total corrections versus photon energy for epoch 37 files, in eV, are given in the figures below, for the ACIS-I and ACIS-S aimpoint positions specifically. We note here that corrections a various points across the chip surface may be rather different, even very significantly so, from these results.

Fig. 1: Comparison of the total change in eV due to the Epoch 35, 36, and 37 T_GAIN files, for the I3 aimpoint. The red curve is for Epoch 35,
and interpolates between the epoch 35 and 36 corrections at the mid-point (average). The 2008-11-01 files are for Epoch 36. The t_gainN0006.fits file
replaces the t_gain_biN0002.fits file, and there is very little change at this location on the chip by this upgrade. Other locations will vary more
significantly. The acisD2009-02-01t_gain_biN0002.fits file is a flat, non-interpolating file, and will be upgraded after Epoch 38 has been
completed (May 1-Aug 31, 2009).

Fig. 2: A similar plot for the aimpoint of the BI chips S3, with the CTI corrections applied to the data. For this location and chip the 2008-08-01 file
upgrade is more significant (difference between the solid green and dashed blue curves), but mainly at the highest energy points above 6 keV. For
the new flat file (cyan dashed curve) more correction seems to be required above 5 keV than in the previous epochs, but not out of the ordinary. This
result may be modified by the next epoch data as well.

Fig. 3: The S3 aimpoint corrections for the case where the BI chips are NOT CTI-corrected at all. (The N0005 files.) As is usually the case,
the corrections are more scattered over the full range for the non-CTI case. However while these variations are significant relative to the
0.3% gain setting standard for the calibrations, they are not unusually strong. The cyan dashed curve indicates the strongest variation in
correction values over the range, but again it may be modified in the next epochal release.

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