Chandra X-Ray Observatory

CDA - Public Data

Data Analysis Links
CDA Status
  • The archive is fully functional.
Reprocessing Status
    Reprocessing IV has been completed in December 2014.
Current Software Releases
  • ASCDSVER: 10.12.4
  • 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
Information about Public Data in the Chandra Data Archive

What Is Available?

There are two types of observations that are in the public domain: calibration observations; and GTO (guaranteed time observation), GO (guest observer), TOO (target of opportunity), DDT (director's discretionary time) observations for which the proprietary period has expired.

Click here for a list of GTO/GO/TOO/DDT observations that have been released to the public domain. All these observations may be downloaded through the same interface as the Calibration observations. We recommend the use of ChaSeR.

See the package listings for the standard data products packages that are available.
There is a more extensive (though not up-to-date) Guide to Chandra Archive Data Products.

Note, by the way, that not all data products belonging to proprietary observations are proprietary: only those that really contain proprietary information.

What is being made available is always the highest version of the products that is approved by V&V; this default version is considered to contain the highest quality data products that are available. The data products version is identified in each individual product by the value of the REVISION keyword. Older versions may be obtained by a special request to Archive Operations. Please provide: the ObsId, the version (revision number), and the data products requested, as well as an explanation why this version, rather than the default version, is required.

The FITS headers of the data products contain keywords that identify the CalDB and software releases used for their creation.

Public Release Dates and Public Data Retrieval

Public release dates are listed via the CXC-DS processing status tool.

There are two columns of interest:

  1. Data rights
  2. Public release date

Data Rights

The Data Rights column indicates the length of the proprietary period and may contain any one the following:

  • S: one year
  • D: 3 months
  • N: none
  • or a number indicating the number of months

The proprietary period starts when the PI is notified that the data may be downloaded. This will not happen until the products have been approved by V&V. That does not mean that the data have to be perfect but they must be seriously useable. If the products are rejected by V&V the PI is sent a copy of the V&V report. When the user decides that (s)he wants to work with the data anyway, that request is granted and the proprietary clock is started. Another option is to request Custom Processed data at that point - the shipping of which also starts the proprietary clock.

There is one important qualification to the procedure described above: the proprietary clock only starts ticking when at least 90% of the approved time, by SeqNum, has been made available for download.

Public Release Date

The Public Release Date provides the date when proprietary data are released to the public domain. Although there is a date for every ObsId, the rule is that the proprietary clock is started as soon as the 90% mark is reached for the entire SeqNum and the release dates are set accordingly.

For an explanation of the relation between ObsIds and SeqNums, click here.

This page maintained by the Chandra Data Archive (

Last modified: 2020-04-06

Smithsonian Institute Smithsonian Institute

The Chandra X-Ray Center (CXC) is operated for NASA by the Smithsonian Astrophysical Observatory. 60 Garden Street, Cambridge, MA 02138 USA.   Email: Smithsonian Institution, Copyright © 1998-2024. All rights reserved.