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
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
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
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
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:
- Data rights
- Public release date
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 80% 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
80% mark is reached for the entire SeqNum and the release dates are set
For an explanation of the relation between ObsIds and SeqNums, click