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CalDB PUBLIC Release Notes
Effective Date: (UTC) 2009-03-26T18:00:00
(Not installed in SDP.)
Public Release Date: 27 March 2009
Version: 4.1.2
Release Type: PUBLIC

I. Introduction

CaldB 4.1.2 is an upgrade to CalDB 4.1.1. It includes the following upgrades:
 Only the new ACIS T_GAIN affects current observations and processing in any immediate way. See the technical details (Section III below) for information about how the other changes may affect certain analyses.

User Documentation:
"How CalDB 4.1.2 Affects Your Analysis"
http://cxc.harvard.edu/ciao/releasenotes/ciao_4.1_release.html#HowCALDB4.1.2AffectsYourAnalysis

II. Summary of Changes

A. ACIS T_GAIN Epoch 36

LOCATION: $CALDB/data/chandra/acis/t_gain/
FILENAMES: acisD2008-08-01t_gainN0005.fits
                         acisD2008-08-01t_gainN0006.fits
                         acisD2008-11-01t_gain_biN0002.fits
                         acisD2008-11-01t_gainN0002.fits

The latest T_GAIN files cover the 01 Nov 2008 through 31 Jan 2009 period, and include filenames listed above. 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 2008-08-01T00:00:00. All earlier data are unaffected by this change.

Users analyzing observations with DATE_OBS later than 2008-08-01 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. Correction to header keyword "CTI_APP" in ACIS -120C CTI files version N0005

LOCATION: $CALDB/data/chandra/acis/cpf
FILENAMES: acisD2000-01-29ctiN0005.fits
                         acisD2002-08-01ctiN0005.fits

We have discovered recently that CalDB 4.1.0 and 4.1.1 have been released with an error in the first extension HDU in the value assigned to header keyword "CTI_APP". It should have been set to "PPPPPNPNPP", but was instead set to "PPPPNPNPP" (one character short). This will cause problems for reprocessing with acis_process_events, when attempting to select CTI, DET_GAIN, and T_GAIN files in a_p_e when the CTI_APP keyword has already been set to the value "PPPPPNPNPP", the proper value for this configuration of CTI corrections. (In this configuration, parallel CTI correction has been or will be applied to all FI chips, and no CTI correction at all will be or has been applied to the BI chips.)

While the default and recommended configuration for new processing is to do CTI correction on all 10 chips (the configuration CTI_APP=PPPPPBPBPP), the archive has most ACIS observations already processed with the PPPPPNPNPP. While these data do not need to be reprocessed to maintain this CTI configuration, we want to be sure that users who do wish to run reprocessing with the PPPPPNPNPP configuration are allowed to do so, simply by pre-setting CTI_APP in their respective L1 events file headers, and then proceeding with the thread.

Users who prefer to work with the default, and optimal, CTI correction configuration (PPPPPBPBPP) are not at all affected by this change. Nor are users who do not reprocess data from the archive with a_p_e!

Pipes/Tools affected:
CIAO tool acis_process_events
(Note that SDP is not affected, as it will never apply the N0005 configuration to new data, as this is not the default, nor the optimal CTI configuration.)

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

C. Modification of CVSD*/CVST* keyword sets for all ACIS -110C calibration files

We have discovered a problem for one particular observation (OBS_ID=62538) taken in September 1999, with ACIS focal plane temperature (FP_TEMP) set to 164.0K or -109.15C, which has TSTART= 53736853.886 sec, and DATE-OBS = 1999-09-14T22:54:13 (UTC). This turns out to have been the first science observation with the newly lowered FP_TEMP for -110C ACIS operations. Our previous CVSD0001 for -110C has always been (UTC) 1999-09-16T00:00:00. Upon further review of the ACIS housekeeping data from that period, we have learned that a better date would have been 1999-09-14T20:00:00, so that 62538 can automatically access the -110C L1 and downstream calibration data from CalDB. Hence the CVSD and CVST values for all -110C calibration files in CalDB will be updated to this latter new value.

Here is a table of the affected file types, filenames, and paths in CalDB4.
PRODUCT
 FILENAME
 PATH
CalDB4
 EXTENSION #
 DM BLOCK #
BADPIX
 acisD1999-09-16badpixN0002.fits
 $CALDB/data/chandra/acis/badpix/
 1-10
 2-11
BKGRND
 acis0iD1999-09-16bkgrndN0002.fits
 $CALDB/data/chandra/acis/bkgrnd/
 1
 2
acis1iD1999-09-16bkgrndN0002.fits
 1
 2
acis2iD1999-09-16bkgrndN0002.fits
 1
 2
acis2sD1999-09-16bkgrndN0002.fits
 1
 2
acis3iD1999-09-16bkgrndN0002.fits
 1
 2
acis3sD1999-09-16bkgrndN0002.fits
 1
 2
acis5sD1999-09-16bkgrndN0002.fits
 1
 2
acis6iD1999-09-16bkgrndN0002.fits
 1
 2
acis6sD1999-09-16bkgrndN0002.fits
 1
 2
acis7iD1999-09-16bkgrndN0002.fits
 1
 2
acis7sD1999-09-16bkgrndN0002.fits
 1
 2
acis8sD1999-09-16bkgrndN0002.fits
 1
 2
acis9sD1999-09-16bkgrndN0002.fits
 1
 2
DET_GAIN
 acisD1999-09-16gainN0005.fits
 $CALDB/data/chandra/acis/det_gain/
 1
 2
acisD1999-09-16gainN0006.fits
 1
 2
FEF_PHA
 acisD1999-09-16fef_phaN0002.fits
 $CALDB/data/chandra/acis/fef_pha/
 1
 2
OSIP
 acisD1999-09-16osipN0006.fits
 $CALDB/data/chandra/acis/osip/
 1
 2
acisD1999-09-16osipN0007.fits
 1
 2
P2_RESP
 acisD1999-09-16p2_respN0005.fits
 $CALDB/data/chandra/acis/p2_resp/
 1-5
 2-6
T_GAIN
 acisD1999-09-16t_gainN0005.fits
 $CALDB/data/chandra/acis/t_gain/
 1
 2
QEU
 acisD1999-09-16qeuN0002.fits
 $CALDB/data/chandra/acis/qeu/
 1-10
 2-11

Only reprocessing and analysis of OBS_ID 62538 is affected by these changes. 62538 is a calibration observation of HR1099, using the HETG/ACIS-S configuration. Hence, acis_process_events, tg_resolve_events, fullgarf, mkgarf, mkinstmap, and acis_bkgrnd_lookup will be affect for this observation, in that the CalDB file searches will select the above files correctly.

III. Technical Details

A. ACIS T_GAIN Epoch 36

The total corrections versus photon energy for epoch 36 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.

supporting/i3_aimpt_E36v6.gif
Fig. 1: Comparison of the total change in eV due to the Epoch 34, 35, and 36 T_GAIN files, for the I3 aimpoint. The red curve is for Epoch 34,
and interpolates between the epoch 34 and 35 corrections at the mid-point (average). The 2008-08-01 files are for Epoch 35. 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 acisD2008-11-01t_gain_biN0002.fits file is a flat, non-interpolating file, and will be upgraded after Epoch 37 has been
completed (Feb 1-April 30, 2009).

supporting/s3_aimpt_E36v6.gif
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.

supporting/s3_aimpt_E36v5.gif
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.

C. Modification of CVSD*/CVST* keyword sets for all ACIS -110C calibrations

The figure below gives a plot of the ACIS house-keeping data during the period of 10-21 Sept 1999, and it is immediately obvious that there was a process of several variations in the FP_TEMP in the lowering of the ACIS temperature at this (very early) point in the mission. the vertical blue dashed lines indicate the extent in time of Obs_ID 62538.
The red dashed line indicates the previous CVSD for -110C ACIS operations. The black vertical dashed line indicates the new value to be used.

supporting/fp_temp.gif


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