The third reprocessing series consists of one large reprocessing
project and a few smaller ones:
- Reprocessing III: Uniform calibration of almost all
data in the archive
This run consists of a complete reprocessing of all data
obtained between 29 January 2000 and 15 November 2005. The aim of this
run was to provide a complete set of archived data, processed with a
uniform calibration database from the moment the frontend temperature
went to -120° C, in January 2000. Details of the changes may be
found below. This bulk of this processing run was
performed between February 2006 and June 2007.
- Reprocessing IIIa: Aspect correction for early 2007
During the August 2007 we reprocessed observations made
between December 2006 and May 2007, using an updated aspect
calibration. That correction is only needed for this particular set of
It affects all data obtained after 2006-12-10
and processed on or before 2007-05-22. These data were subject to a
systematic aspect offset of approximately 0.4 arcsec, believed to be
the result of a changed thermal environment following the procedure
to cool the ACA CCD from -15° C to
-19° C that took place between late Nov-2006 and early
Jan-2007. This error has been corrected in the newly processed
version of the data.
More information is available at this location.
- Reprocessing IIIb: Override Obspar
- Reprocessing IIIc: Calibration update of all HRC-I
observations since 29 January 2000
The following concerns HRC-I observations only and is of interest to
you if one or more of the following apply:
- you have performed hardness ratio or quantile color-color
- your analysis was particularly sensitive to the Enclosed Count
- your sources were close to on-axis in observations witha large
- Reprocessing IIId: Problem Obsids
Reprocessing III: Uniform calibration of almost all data in the archive
Summary of Changes for Reprocessing III of Chandra Data
The main component of the third reprocessing run of Chandra
data was started in
February 2006 and covers most of the mission. It began with data
from January 2005 and ran through November 2005; then it went
back to December 2004 and is running backwards to the moment when the
frontend temperature went down to -120° C, in January 2000; the very
early part of the mission may be reprocessed later.
The quality of the reprocessed data will be better because of
improvements in software and, especially, calibration since the
current default data in the archive were created.
Whether the new data version would affect any scientific conclusion
drawn on the basis of the older versions depends on many factors: the
nature of the conclusions, the type of analysis, the signal-to-noise
ratio, etc. Ultimately, the user may need to make a comparison in order
to judge whether the changes are significant for her or his purposes,
but to aid in that assessment we have summarized in the following
tables the most significant CalDB and software changes. There are three keywords in the
headers of all CXC FITS data products that
indicate what version those products were processed with:
- DATE: The date and time of the file's
creation (in UTC)
- ASCDSVER: The CXC-DS
software release version used
- CALDBVER: The CalDB
version used for creating the data product
The values of these keywords should be looked up in older versions of
data products and used when consulting the tables below in order to
determine whether reprocessed products may differ significantly.
Note also, that the new products will be fully compatible with the
current version of CIAO, something that is not necessarily the case
for older data versions.
Major CalDB Changes
The following is a short summary of Chandra calibration
upgrades that have affected various aspects of pipeline processing
since the completion of the previous (second) round of
reprocessing. The specific relevant portions of the
are ACIS, HRC,
PIXLIB (coordinate library), and
|-120° C Version N0003: Status bits
changed on node boundary chips
so they are not counted as normal bad columns. Hence adjacent
columns will not be automatically included in the
*bpix1.fits primary data files.
|Version N0005 Epochs 1-22 (to May 2005)
Due to the CTI time-dependence added in
CTI N0005 files below,
T_GAIN is now approximately re-zeroed at
the start of Epoch 11, which is August 1, 2002, for the
FI chips ONLY!
BI chips T_GAIN
corrections have not yet been affected by CTI
correction, because no CTI
correction has been released for them.
Epochs 21 and 22 are added; however all files have been changed
to include a higher-density spatial grid, which eliminates a
calibration problem, to wit a gain-sag most notably at high
energies near the central 50 columns of each chip.
|CTI files version
N0005, time-dependence added to
to account for decay in their resolution with time. Two files
have been included, for T_GAIN epochs 1-10
and 11-current. Only the S2 data for epochs
1-10 are updated with a better model.
(BI chip CTI
corrections are not yet included.)
|An improved bad pixel map
|Time-dependent gain corrections to the PHA
in Level 1
|Phase 2 response gains for Chips 4, 8, and 9 (S0,4,5), making the
set complete for use with mkacisrmf.
|S1-3, I0-3 gain function modifications (improved gain model) near
the Si-K edge
|S1 gain function improvements for imaging and grating
|Gain maps included in processing for HRC-I for the first time,
version N0001. Second file applies to all
data after HV
was reduced in the HRC-I, on 1999-10-04.
|Improved gap removal calibrations for HRC-S. For a complete
N0002: This file is the first iteration
of corrections for the known non-linearity in the HRC-S/LETG
spatial wavelength scale that has been frequently alluded to in
|Upgrades to the bad pixel map for HRC-S.
This new file has a time-dependent addition for a rectangular
hot spot on plate 1 of HRC-S, which recently became enlarged.
|Upgrades to the bad pixel map for HRC-I
|Upgrades to event tests to eliminate ghost images and some background
events, such as event flatness, tapringing, amplifier saturation,
and f-p test
|HRC-S GAIN and PI
region filters for background elimination
|Improved gap removal calibrations for HRC-I
|Astrometry corrections to within 0.2 arc seconds on axis, in
particular for ACIS
|Version N0002, HRC-S imaging default
|Improved chip corner positions to correct the HETG/ACIS-S
wavelength/energy scale to within prelaunch specifications.
Version N0005 includes ACIS-S chip corner
for chips 4, 5, 6, 8, and 9. (ACIS-I0-3 and ACIS-7 are not changed.)
These corrections, while having negligible affect on the imaging
astrometry for ACIS-S, eliminate wavelength errors of the order
.002 Angstroms in the HETG and LETG spectra with ACIS-S. Further an
adjustment to the MEG period has been included, which makes the HEG
and MEG spectra more mutually consistent.
|Off-axis astrometry improvements for outlying ACIS chips.
spectra more mutually consistent.
Other areas of the CalDB have been significantly upgraded since the
second reprocessing run, e.g., the response input data for ACIS
(CalDB 3.2.0), the spatially-dependent
ACIS OBF contamination correction (CalDB 3.0.0),
the LSF parameter
input data for grating RMFs (CalDB 2.27, 2.28),
the upgrades in the
detector quantum efficiencies and uniformities (CalDB 2.9 for HRC-I,
2.28 for ACIS, 3.0.1 for HRC-S), and the HRMA effective area
modifications (CalDB 3.2.1). However, these do not directly affect
processing through Level 2 which is the work of the current reprocessing
run. Nevertheless, the reprocessing of the older data does allow
these new analysis-level calibrations to be applied more appropriately
and directly to archival data (i.e. without user reprocessing or
custom processing). Hence reprocessing will make the latest and best
Chandra calibrations more immediately applicable for the bulk of the
Major Software Changes
Updates will that will change and/or improve
standard pipeline data products
|DS software version
- In ACIS CC-mode, the values of PHA,
in an event file change because of a
CALDB interface change. (see also an
update in DS7.6.3).
- The ACIS destreak tool is updated to fix problems using all
events instead of only using good events. This only affects data
taken in the ACIS S4 chip (or ccdid=8).
- Other minor changes affecting both ACIS and HRC data, including
a bug fix in the axis of rotation in the aspect solution
and updating a GTI limit for the HRC
Next-In-Line time gap.
- The headers in ACIS and HRC event files are upgraded to reference
other data products, including CALDB
files (e.g., ASOLFILE = aspect
solution, THRFILE = ACIS split
- For ACIS-CC-mode, the CTI correction
is applied and the split-threshold file is correctly utilized.
PHA/PI/ENERGY values in an event file
(see also an update in DS7.6.4).
- In calculating the aspect solution, the aspect pipeline properly
applies the proper motion of a guide star. This will slightly
improve the accuracy
of the aspect solution. Previously, a guide star with a large
proper motion is excluded in calculating the aspect solution.
- Add support for large files (> 2GB).
Previously, when an event file is bigger than 2 GB (for long
observations of very bright sources), pipeline s/w could not
handle it and had to apply manual intervention either by removal
of non-vital columns or by splitting into multiple smaller
- Changes in VV aspect check limits.
Minor changes in aspect quality limits (e.g., image centroiding
error, offset) are applied in determining a bad guide star or
fid light to exclude in calculating the aspect solution.
- Update AGASC (
AXAF Guide and Acquisition Star
Catalog) to v1.6.
This slightly improves aspect quality and absolute position
this page for more information.
- ACIS hot pixel tools are added to the ACIS L1 pipeline
to effectively flag both hot and after-glow (transient) pixels.
The tool acis_detect_afterglow was removed from the pipeline.
- The ACIS EXPNO column has a real
data-subspace with a specified range of exposure numbers in each
GTI per chip.
- Fixed ACIS TGAIN computation that
affects very high PHA values (above
~4100 ADU). PHA,
ENERGY values will be different.
- For ACIS-S + LETG, the spectral extraction width changes from
1.33e-03 deg to 2.00e-3 deg to compensate for a residual rotation
of dispersed spectra.
- Fixed contents of ACIS mask files when
SAMP_CYC (sampling cycle) is not 0 or 1.
|No change (most data are still labeled as 7.3.0)
- ACIS time dependent gain correction added to the ACIS L1
ENERGY values in the event file will
- ACIS destreaking is applied to the S4 chip in the ACIS L1
pipeline. (Note. It is later improved in
DS 7.6 started on 2005-11-15.)
- ACIS+CC mode data processing (e.g., algorithm to determine
chip-y coordinate) is enhanced. Note that more enhancements for
the CC mode are later added in
DS7.6.3 (2005-09-01) and
- Several minor changes to ACIS mask files. One row specifies that
a chip is on or off. The columns PHAMIN
and PHAMAX were updated. The columns
OVERLAP were dropped. The keywords
LASTROW were updated.
- HRC AMPSFCORR test is turned on to
properly deal with tap-ringing induced errors.
- HRC dead time correction factors is corrected for a
double-counting problem in the rate-scalars.
- HRC chip offsets are changed based on the LETG analysis.
Chip positions and all coordinates will change.
- Pixel randomization is turned off for all HRC and all grating
datasets when going from chip to angular coordinates.
- Fixed a sign error in the grating angle for LETG data for both
ACIS and HRC. This will change both resolved events and grating
- A new fits header keyword as a dataset identifier,
DS_IDENT is added. Its value is for
- The Level2 merged products (only for multiple obi data) retain
more per-obi header keywords (e.g.,
based on relaxed merging rules.
|No change (most data are still labeled as 7.2.1)
- Fixed a systematic timing error by adding 285 microseconds (to
strip files by PI3)
|No change (some data labeled as 7.0.2)
- Significantly enhanced infra-structure including CIAO 3.0 tools
integrated into the pipeline processing and upgraded telemetry
processing (PI3 replacing an old
- Revised a chip y-coordinate (CHIPY) in
ACIS continuous clocking (CC) mode,
when finding the correct position-dependent gain for an event.
An estimate of the actual CHIPY
location of the source is used instead of the recorded value of
CHIPY, which represents time instead
- Fixed a problem with the way the keywords
CTIFILE are populated.
CTI_CORR is set to
T if and only if the
CTI adjustment is applied. Likewise,
CTIFILE is populated with the name of a
CTI adjustment file if and only if the
CTI adjustment is applied.
- Fixed a problem in using a
CTI-corrected gain file (implemented in
DS6.11) for graded mode data (no
PHAs in the grade mode to correct
- The HRC tap ringing correction algorithm was implemented.
All the coordinates of HRC data will change slightly.
- Adjusted HEG and MEG region width scaling factors (20 to 35) and
background outer limits (from 23.9 to 21.6) in the grating L1.5
pipeline. See more in
- The observation parameter (obspar) files was upgraded to
version=6. Because the data type of the ObsId is changed from
integer to string, all old obspar files can not be used after
7.0.0. Other changes include sim_z_offset updated in the actual
obspar based on the SIM telemetry.
- Upgraded a SIM stripper which produces
a single strip file for both A and B, but
SIM-A and SIM-B
L0 products remain separated. There should be no change to the L0
products, however, the bogus SIM-B L0
products will no longer be created.
- Added support of the 2nd Inertial Reference Unit
(IRU2) switchover to the
ASPECT L1 pipeline. The aspect
solution changed only slightly (~0.01 arcsec).
|6.12.0 (6.11.0 deployed at the same time)
- The observation parameter (obspar) files was upgraded to
version=5 to support the enhanced roll and time window
constraints started to use in an observing cycle AO5.
|6.11.0 (deployed at the same time as 6.12.0)
- ACIS CTI (Charge Transfer Inefficiency)
correction was applied for ccdid = 0-3
and 6 (or I0-I3 and S2) taken at a ccd temperature of -120°
C. It will change PHA,
ENERGY and PI
values in ACIS event files
- Fixed incorrect sky field-of-views (in
in acis...full_img2.fits) for
observations with multiple observational intervals
- Fixed a s/w bug in resolving events of grating
CC mode data for using incorrect chip
coordinates and angular coordinates.
- Applied a correct trigonometric function instead of a small
angle approximation (sin(a) ~= a) for the coordinate
transforms in the grating pipeline
- Fixed a problem in the ASPECT L1
pipeline when the first input file has no data.
- Upgraded to the AXAF Guide and
Acquisition Star Catalog (AGASC) from
1.3 to 1.5 (see more in
- Fixed the computation of DTCOR for
Reprocessing IIIa: Aspect correction for early 2007
Follow this link.
Reprocessing IIIb: Override Obspar
Reprocessing IIIc: Calibration update of all HRC-I observations
since 29 January 2000
During the third Chandra Reprocessing run (January 2006 - September 2007)
all observations since 29 January 2000, including those made by HRC-I,
were processed with a new common set of calibrations.
However, since the start of that run there have been significant
improvements in two calibration areas for HRC-I: the gain map
(GMAP) and DEGAP
(GAPLOOKUP). We have decided to perform a
supplemental reprocessing of all HRC-I observations since Feb 2000 in
order to update all of them to the latest gain and degap calibrations;
This is designated as Reprocessing Run 3C.
The GMAP is used to generate
PI values from PHA
values in the event list. The PI values may be
used to estimate hardness ratios, and to perform quantile
color-color analyses of HRC-I observed sources. If your analyses have
included hardness ratios or quantile color-color analysis, or you would
like to perform such analyses of your sources, you may wish to review
the Repro 3C processing of your observations.
The upgrades to the GAPLOOKUP tables (see
section III.B of the
CalDB 3.4.1 Release Notes)
for HRC-I have made minor, but still significant improvements to the
encircled energy fraction for on-axes sources
located at or near the nominal aimpoint position of HRC-I. The latest
upgrade to GAPLOOKUP, which has been added as
of September 14, 2007, makes significant
improvements in the degap solution for on-axis source observations with a
particular large SIM_Z offset, so that the
source appears in CRSU = 12-13 region,
and small improvements elsewhere. If your analyses are particularly
sensitive to the ECF, you may want to review
your results with the Repro 3C processing of your observations.
Reprocessing IIId: Problem Obsids