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CDA Status
  • The archive is fully functional.
Reprocessing Status
    Reprocessing IV has been completed in December 2014.
Current Software Releases
  • ASCDSVER: 10.12.6
  • CALDBVER: 4.11.1
What's New
  • Electrical Outage 11/05/21 - 11/06/21
    There will be a planned electrical outage Friday, November 5 2021, 5:30PM - Saturday, November 6 2021, 6:00PM EDT. During this time period ChaSeR and other archive interfaces will be unavailable.
  • Electrical Outage on 07/28/21
    There will be a planned electrical outage Wednesday, July 28 2021, 8:00PM - 10:00PM EDT. During this time period ChaSeR and other archive interfaces will be unavailable.
  • Downtime on 6/12/21
    Due to electrical work, the public interfaces of the Chandra Data Archive will not be available on Saturday 6/12 from 4 AM to 9 PM.
  • Repro V Begins
    The fifth major reprocessing of the archive (Repro V) has started! Details can be found here.
  • Past Notices
History of Software and CalDB Releases for Data Products in the Chandra Data Archive

This page provides a summary of the changes, significant for the science data in the archive, that were implemented in subsequent CXC software and CalDB releases used in Standard Data Processing.

CalDB Releases

The CalDB version may be identified through the FITS keyword CALDBVER.

Software Releases

The SDP software version may be identified through the FITS keyword ASCDSVER.

  • Release notes for software versions 6.0.0 (May 2001) through 6.9.0 (September 2002) are available from a separate web page.
  • Software from version 6.9.2 (October 2002) onward.

Major CalDB Changes


The following indicate upgrades to the calibration or the ACIS instrument as apply to standard data processing (ACIS Level 1 and 2).

Date CalDB version Component Description
2008-09-10T15:30 3.5.0 T_GAIN T_GAIN corrections for Epoch 34 (May - July 2008)
2008-06-16T17:00 3.4.5 T_GAIN T_GAIN corrections for Epoch 33 (Feb - Apr 2008)
2008-03-27T13:53 3.4.3
  • T_GAIN
T_GAIN corrections for "Epoch 0" (Sep 1999 - Jan 2000) T_GAIN for BI chips only, with appropriate DET_GAIN updates for the BI chips, including the much improved ACIS-S1 gain tables.
2008-03-27T13:53 3.4.3 T_GAIN T_GAIN corrections for Epoch 32 (Nov 2007 - Jan 2008)
2007-12-12T13:00 3.4.2 T_GAIN T_GAIN corrections for Epoch 31 (Aug-Oct. 2007)
2007-09-19T14:30 3.4.1 T_GAIN T_GAIN corrections for Epoch 30 (May-July 2007)
2007-05-22T12:00 3.4.0 T_GAIN T_GAIN corrections for Epochs 28 (Nov 2006 - Jan 2007) and 29 (Feb - Apr 2007)
2006-12-13T16:01 3.3.0 T_GAIN TGAIN updates for Epoch 27 (Aug - Oct 2006)
2006-11-12T14:50 3.2.4 T_GAIN
  • T_GAIN updates for Epochs 25 (Feb 2006 - Apr 2006) and Epoch 26 (May - July 2006);
  • T_GAIN UPGRADES for all of Epochs 21-24, including adjustments made for the gain discontinuity that appeared on 1-2 August 2005 in ACIS-I0 and ACIS-I2. These were necessary to remove interpolations across the discontinuity dates
2006-03-06T16:00 3.2.2 T_GAIN Time-dependent gain correction (T_GAIN) updates for Epoch 23 (Aug - Nov 2005) and Epoch 24 (Nov 2005 - Jan 2006) for the CTI configuration CTI_APP=PPPPPNPNPP, or Parallel CTI correction for FI chips, and NO CTI correction for the BI chips.
2005-12-15T17:30:00 3.2.1 BADPIX -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.
2005-11-16T16:00:00 3.2.0 CTI
  • 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.
2005-11-16T16:00:00 3.2.0 DETGAIN CTI files version N0005, time-dependence added to FI chips 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.)
2005-11-15T15:30:00 3.2.0 BADPIX An improved bad pixel map
2005-06-23T15:17:00 3.1.0 T_GAIN Time-dependent gain corrections to the PHA in Level 1
2005-06-23T15:17:00 3.1.0 CTI Phase 2 response gains for Chips 4, 8, and 9 (S0,4,5), making the set complete for use with mkacisrmf.
2004-12-14T18:00:00 3.0.0 DETGAIN S1-3, I0-3 gain function modifications (improved gain model) near the Si-K edge
2004-12-14T18:00:00 3.0.0 DETGAIN S1 gain function improvements for imaging and gratin (order-sorting) observations


The following table includes upgrades to the HRC-I and HRC-S L1 and L2 calibration files.

Date CalDB version Component Description
2007-09-19T14:30 3.4.1 DEGAP HRC-I: Degap solution correction for large negative SIM_Z offsets; Currently important for only to one or two observations.
2007-05-06T15:00 3.4.0 GAIN MAP HRC-I: Refinements of the time-dependent gain maps in CalDB 3.3.0. These are the current calibration standard for HRC-I GMAPs.
2006-12-13T16:01 3.3.0 GAIN MAP HRC-I: Time-dependent gain maps, spaced approximately annually along the mission time line. These data are upstaged by CalDB 3.4.0 (see the next row of the table).
2006-08-10T15:30 3.2.3 GAIN MAP HRC-I: Correction to 1998-10-30 gain map registration
2006-08-10T15:30 3.2.3 DEGAP HRC-I: Improved on-axis degap solution
2005-11-16T16:00:00 3.2.0 GAINMAP 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.
2005-11-16T16:00:00 3.2.0 DEGAP
  • Improved gap removal calibrations for HRC-S. For a complete description, see this page.
  • GAPLOOKUP version 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 the literature.
2004-08-11T19:30:00 2.28 BADPIX 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.
2002-04-04T15:05:00 2.13 BADPIX Upgrades to the bad pixel map for HRC-I
2002-11-08T00:00:00 2.4 EVENT FILTER Upgrades to event tests to eliminate ghost images and some background events, such as event flatness, tapringing, amplifier saturation, and f-p test
2001-03-07T14:50:00 2.3 EVENT FILTER HRC-S GAIN and PI region filters for background elimination
2001-01-25T18:00:00 2.2 DEGAP Improved gap removal calibrations for HRC-I


The following upgrades to the Aspect calibration files are relevant for observations taken since the lowering of the Aspect Camera CCD operating temperature, and to the shut-off of the ACIS detector housing heater assembly. Observations taken before the relevant dates in the descriptions given are not affected by these upgrades, and no ASPECT reprocessing or correction is needed for observations downloaded from the current archive, unless otherwise indicated in the ObsID summary pages.

Date CalDB version Component Description
2008-04-02T00:00 3.4.4
The change here is to add a third BINTABLE to the ALIGN/FID_POS files, namely the FID_COR table, needed after the ACIS Detector Housing Heater shutoff, which took place during April of 2008.
2007-05-06T15:00 3.4.0
Two new ALIGN/FID_POS epochs have been added, for effective from the dates 2003-06-09T00:00:00 and 2006-12-10T00:00:00. The cooling of the ASPECT CCD began on 2006-12-10. Minor astrometric corrections beyond 2002-12-01 are included in the 2003-06-09 file.
2003-12-30T14:00:00 2.25 ASTROMETRY Astrometry corrections to within 0.2 arc seconds on axis, in particular for ACIS


Date CalDB version Component Description
2005-02-15T16:45:00 3.0.1 AIMPOINTS Version N0002, HRC-S imaging default aimpoint added.
2005-02-15T16:45:00 3.0.1 GEOM
  • Improved chip corner positions to correct the HETG/ACIS-S wavelength/energy scale to within prelaunch specifications.
  • Version N0005 includes ACIS-S chip corner positions modifications 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 Anstroms 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.
2001-10-22T16:00:00 2.9 GEOM 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.

Major Software Changes

Updates since Version 6.9.2

Date DS software version Description
2008-08-21 No change
2008-07-16 No change
  1. The aspect pipeline is updated to handle ACIS detector housing cooling which is newly implemented in operation. see more in a memo)
  1. The telemetry s/w is updated to support a new telemetry template (P009).
  2. The fits file header problem with a long target name (more than 80 characters) is fixed.
  3. The HRC bit in HRC housekeeping level 0 files (hrc*hk0.fits,) is properly set to follow the FITS convention.
  1. The EPHIN pipeline is updated to handle when the EPHIN G detector HV (high voltage) being turned off.
2007-12-12 No change
2007-10-17 No change
2007-09-05 No change
2007-07-10 7.6.11 No change
2007-01-09 7.6.10
  1. The ACIS serial charge-transfer inefficiency (CTI) adjustment is properly applied for ACIS back-illuminated CCDs S1 and S3 chips at -120C. This s/w upgrade is associated with CALDB Version 3.3.0.
  2. The 'expno' data-subspace is reset in L2 files so that multiple data can be cleanly merged.
2006-09-13 7.6.9 No change
  1. The aspect pipeline is updated by adjusting a parameter indicating the allowed maximum space craft rate to properly handle the data during the momentum dump and perigee passage.
2006-06-13 7.6.8
  1. The HRC pipeline is updated to fix a bug in calculating an HRC dead time correction factor when the HRC observation mode changes to NEXT-IN-LINE before the end of the observation boundary.
  2. The value of the keyword TIMEDEL in some ACIS continuous-clocking mode event-data files was incorrectly set to 1.4592 s instead of 0.00285 s. While this does not represent a problem if the pipeline-produced files are used for timing analyses, it is a problem if an affected event-data file is reprocessed using acis_process_events with the parameter calc_cc_times=yes because the values of the TIMEs in the output file will be corrupted. The problem, which affected data processed with DS7.6.0 (June 2005) through DS7.6.7, was corrected is DS7.6.8 (June 2006).
2006-04-11 No change
2006-03-07 No change
2006-02-15 7.6.7 No change
2006-01-10 7.6.6 No change
2006-01-01 No change
2005-12-05 No change
2005-11-15 7.6.4
  1. In ACIS CC-mode, the values of PHA, PI, ENERGY in an event file change because of a CALDB interface change. (see also an update in DS7.6.3).
  2. 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).
  3. 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.
2005-09-01 7.6.3
  1. 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 threshold).
  2. For ACIS-CC-mode, the CTI correction is applied and the split-threshold file is correctly utilized. These affect PHA/PI/ENERGY values in an event file (see also an update in DS7.6.4).
2005-07-26 7.6.2 No change
2005-06-15 7.6
  1. 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.
  2. 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 pieces.
2005-05-02 7.5.4 No change
2005-03-23 7.5.3
  1. 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.
2005-02-18 7.5.2 No change
2005-02-15 7.5.1 No change
  1. Update AGASC (AXAF Guide and Acquisition Star Catalog) to v1.6.
    This slightly improves aspect quality and absolute position accuracy. See this page for more information.
2004-12-14 7.5.0 No change
2004-11-30 7.4.0
  1. 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.
  2. The ACIS EXPNO column has a real data-subspace with a specified range of exposure numbers in each GTI per chip.
  3. Fixed ACIS TGAIN computation that affects very high PHA values (above ~4100 ADU). PHA, PI, and ENERGY values will be different.
  4. 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.
  5. Fixed contents of ACIS mask files when SAMP_CYC (sampling cycle) is not 0 or 1.
2004-07-13 7.3.2 No change
2004-06-25 7.3.1 No change (most data are still labeled as 7.3.0)
2004-06-22 7.3.0
  1. ACIS time dependent gain correction added to the ACIS L1 pipeline. PHA, PI, and ENERGY values in the event file will change.
  2. 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.)
  3. 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 DS7.6.4 (2005-11-15).
  4. 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 WINDOW and OVERLAP were dropped. The keywords PHAMIN, PHARANGE, FIRSTROW and LASTROW were updated.
  5. HRC AMPSFCORR test is turned on to properly deal with tap-ringing induced errors.
  6. HRC dead time correction factors is corrected for a double-counting problem in the rate-scalars.
  7. HRC chip offsets are changed based on the LETG analysis. Chip positions and all coordinates will change.
  8. Pixel randomization is turned off for all HRC and all grating datasets when going from chip to angular coordinates.
  9. Fixed a sign error in the grating angle for LETG data for both ACIS and HRC. This will change both resolved events and grating masks.
  10. A new fits header keyword as a dataset identifier, DS_IDENT is added. Its value is for example "ADS/Sa.CXO#obs/01234"
  11. The Level2 merged products (only for multiple obi data) retain more per-obi header keywords (e.g., FP_TEMP, SIM_*, *BEP, BTIM*, *_PNT) based on relaxed merging rules.
2004-04-26 7.2.2 No change (most data are still labeled as 7.2.1)
2004-03-25 7.2.1 No change
2004-03-09 7.2.0
  1. Fixed a systematic timing error by adding 285 microseconds (to strip files by PI3)
2003-12-30 7.1.1 No change
2003-10-06 7.0.3 No change (some data labeled as 7.0.2)
2003-10-02 7.0.2 No change
2003-09-26 7.0.1 No change
2003-09-23 7.0.0
  1. Significantly enhanced infra-structure including CIAO 3.0 tools integrated into the pipeline processing and upgraded telemetry processing (pi3 replacing an old pi2).
  2. Revised a chip y-coordinate (CHIPY) in a 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 of position.
  3. Fixed a problem with the way the keywords CTI_CORR and 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.
  4. 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 CTI).
  5. The HRC tap ringing correction algorithm was implemented. All the coordinates of HRC data will change slightly.
  6. 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 this memo)
  7. 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.
  8. 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.
2003-07-17 6.13.4
  1. Added support of the 2nd Inertial Reference Unit (IRU2) switchover to the ASPECT L1 pipeline. The aspect solution changed only slightly (~0.01 arcsec).
2003-05-06 6.13.0 No change
2003-05-06 6.12.0 (6.11.0 deployed at the same time)
  1. 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.
2003-05-06 6.11.0 (deployed at the same time as 6.12.0)
  1. 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, GRADE, FLTGRADE, ENERGY and PI values in ACIS event files (acis...evt1.fits and acis...evt2.fits).
  2. Fixed incorrect sky field-of-views (in acis...fov1.fits, and in acis...full_img2.fits) for observations with multiple observational intervals (OBI).
  3. Fixed a s/w bug in resolving events of grating CC mode data for using incorrect chip coordinates and angular coordinates.
  4. Applied a correct trigonometric function instead of a small angle approximation (sin(a) ~= a) for the coordinate transforms in the grating pipeline (tg_resolve_events).
  5. Fixed a problem in the ASPECT L1 pipeline when the first input file has no data.
2002-10-16 6.9.2
  1. Upgraded to the AXAF Guide and Acquisition Star Catalog (AGASC) from 1.3 to 1.5 (see more in AGASC interface)
  2. Fixed the computation of DTCOR for interleaved-mode observations.

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