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CIAO 3.3.0.1 Release Notes
Return to: Version History
CALDB 3.2.4 was released on 07 November 2006.
This release contains changes that affect:
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all ACIS data observed from November 2005 through the present
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data from chips ACIS-I0 and ACIS-I2 only, observed from May 2005
through August 2005
Note that there is no compatibility problem if you upgrade to
CALDB 3.2.4, but continue to use CIAO 3.2.2.
Time-dependent ACIS Gain Files
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CALDB 3.2.4 contains new time-dependent ACIS Gain (TGAIN) files
(version N0005) for the periods February-April 2006 (Epoch 25)
and May-August 2006 (Epoch 26). These new files replace the
previous standard processing default file
(acisD2005-11-02t_gainN0002.fits) for all observations
taken on or after UTC=2005-11-01T00:00:00.
These four plots illustrate the degree of change the the
respective new files will produce in comparison with the old
file:
Users working with ACIS data taken during this period may wish
to reprocess to improve the TGAIN calibration in their data.
The DATE-OBS header keyword records the observation
start date. Refer to the plots in the ACIS Time-dependent Gain
why topic to see
how the new TGAIN calibration compares to the previous default
file. Note that unless you are fitting a spectra with oxygen
emission lines, the gain refinement is unlikely to have an
effect on the spectrum larger than the uncertainties in
determining the gain.
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There is an additional set of TGAIN files that need to be
replaced due to a gain discontinuity on I0 and I2 that occurred
around 01 August 2005. These files were replaced so that the
software doesn't interpolate over the discontinuity. The
replacements are:
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acisD2005-02-01t_gainN0005_revA.fits replaces
acisD2005-02-01t_gainN0005.fits
There is virtually zero effect with this change. The
upgrade is done so that the file construction is consistent
with the other T_GAIN files. No reprocessing of
data is recommended for this new file.
-
acisD2005-05-01t_gainN0005_revA.fits replaces
acisD2005-05-01t_gainN0005.fits
There is a significant change from the old N0005 file, as
illustrated by the green versus the dashed blue curves in
the figures that follow. We encourage users to reprocess
line-source data from chips I0 or I2, having DATE-OBS within
the period 2005-05-01T00:00:00 and 2005-08-01T23:59:59.9, to
verify their results from those particular chips. For the
other eight chips, reprocessing should be unnecessary.
-
acisD2005-08-02t_gainN0005.fits replaces
acisD2005-08-01t_gainN0005.fits
The 2005-08-02 file is only different from the 2005-08-01
file in the value of keyword EPOCH1 and the CVSD date. This
makes the delta between the old and new files trivial and
indistinguishable within less than 0.1%.
Note: For ACIS-0 and ACIS-2 chips in the 2005-05-01
through 2005-08-01 period, reprocessing and checking line
spectral results is recommended. Other than that,
unless you are fitting a spectra with oxygen emission lines, the
gain refinement produced by these new files is unlikely to
affect spectra beyond the total uncertainty in the gain
determination itself.
CALDB 3.2.3 was released on 10 August 2006. The calibration
changes in this release affect users of HRC-I data only.
Note that there is no compatibility problem if you upgrade to
CALDB 3.2.3, but continue to use CIAO 3.2.2.
Corrected HRC-I Gain Map
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The HRC team found an error in the
hrciD1998-10-30gainN0001.fits gain map for HRC-I,
released in CALDB 3.2.0 (November 2005). The image in
the file is shifted in the horizontal axis, which results in
hrc_process_events calculating PI values
of zero over a portion of the data. The second HRC-I gain file
released in CALDB 3.2.0, hrciD1999-10-04gainN0001.fits,
does not have this problem. The shift is
corrected in the new gain file,
hrciD1998-10-30gainN0002.fits.
These images are of the
hrciD1998-10-30gainN0001.fits
(left) and
hrciD1998-10-30gainN0002.fits (right)
gain map files (click each image for a larger version):
The dark maroon vertical stripe on the right side of the N0001
image is a region of zero image values, which corrupts the PI
values calculated by hrc_process_events. The scale is
linear, with minimum image value of 0 and maximum of 4.5748. In
the corrected N0002 gain map, the image minimum value is 0.8508
and the maximum value is still 4.5748.
Who Should Reprocess?
If your data was taken before UTC 1999-10-04T12:00:00 and has
been reprocessed between CALDB 3.2.0 and CALDB 3.2.3, the
shifted gain map was applied. The gain file name is stored in
the GAINCORF header keyword:
unix% dmkeypar hrc_evt2.fits GAINCORF echo+
hrciD1999-10-04gainN0001.fits
Remember that the gain map only changes the PI values calculated
by hrc_process_events. Applying the new file will only
affect those analyses which use the PI information for quantile
color-color analysis.
To reprocess the data to apply the corrected gain, follow the
Create a New Level=2 Event File
thread.
HRC-I Degap Correction
-
The new gap lookup table,
hrciD1999-07-22gaplookupN0002.fits, will improve the
encircled energy fraction for any on-axis point sources. This
figure illustrates the encircled energy fraction versus radius
from the source position of the N0001 (black curve) versus the
new N0002 (red curve) files:
The derivation of the gap lookup table is presented in the
memorandum HRC-I
Degap Lookup from Capella Data [http://hea-www.harvard.edu/%7Ejuda/memos/hrci_degap_lookup/capella/degap/degap_lookup.html]. It was developed
using twenty Capella observations taken during the Chandra Cycle
7 observation period.
The new calibration may be applied by reprocessing the data with
hrc_process_events, as shown in the
HRC-I Degap Correction
thread. The degap file will also be applied
automatically if the data is reprocessed to apply the corrected
HRC-I gain file from this CALDB release.
CALDB 3.2.2 was released on 15 May 2006.
Note that there is no compatibility problem if you upgrade to
CALDB 3.2.2, but continue to use CIAO 3.2.2.
Time-dependent ACIS Gain Files
-
CALDB 3.2.2 consists of three new time-dependent ACIS Gain
(TGAIN) files for the May 2005 - November 2005 time period
(Epochs 23 and 24). These new files replace the previous
standard processing default file
(acisD2005-05-01t_gainN0002.fits) for all observations
taken on or after UTC=2005-05-01T00:00:00.
Users working with ACIS data taken during this period may wish
to reprocess to improve the TGAIN calibration in their data.
The DATE-OBS header keyword records the observation
start date. Refer to the plots in the ACIS Time-dependent Gain
why topic to see
how the new TGAIN calibration compares to the previous default
file. Note that unless you are fitting a spectra with oxygen
emission lines, the gain refinement is unlikely to have an
effect on the spectrum larger than the uncertainties in
determining the gain.
PIMMS
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