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PUBLIC
Release Notes
Effective Date: (UTC) 2009-09-18T17:00:00
For use with CIAO 3.4 ONLY!
Public Release Date: 18 September 2009
Version:
3.5.5
Release
Type: PUBLIC
I. Introduction
CaldB 3.5.5 is an upgrade
to all previous CalDB versions 3.x.x. CalDB 3.5.5 is for use only with
CIAO 3.4. It includes the following upgrades:
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.
II. Summary of Changes
A.
ACIS T_GAIN Epoch 38
LOCATION:
$CALDB/data/chandra/acis/bcf/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
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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