Relax! The answer is often: "No, you do not need to reprocess!" Depending on the nature of the release, however, the response could be: "If you reprocess, you will gain X amount of accuracy." In rare cases we may also say: "All users should reprocess to take advantage of this improvement."
In order to determine whether or not to reprocess your particular dataset, there are two pieces of information needed:
In the future, this information will be also organized by science category and instrument, such as "point source, ACIS-S, no grating". The page will be updated with relevant information at every CIAO and CALDB release, so users have a one-stop location to determine if an analysis task needs to be redone.
CIAO release notes: http://cxc.harvard.edu/ciao/releasenotes/CALDB release notes: http://cxc.harvard.edu/caldb/downloads/releasenotes.htmlWhen reprocessing is the best or worst decision
There are two extremes when discussing reprocessing: brand new and very old data. In this case, "new" and "old" are relative to the current version of SDP.
Data that a user has just received from the Chandra X-Ray Center
- e.g. General Observing (GO) projects - has been processed with
the most recent version of SDP. These data have been created
with the newest tools and calibration. In some cases, it is
better than what can be achieved in CIAO, as updates often get
added to SDP sooner than to a CIAO release.
The only reason a user would reprocess this data is to change any of the default parameter settings used in SDP. For instance, an ACIS dataset could be reprocessed to look at the difference between CTI-corrected (the pipeline default) and CTI-uncorrected data.
At the other extreme is very old data. If a user is working with
a dataset that was last processed a few years ago, it may be a
better use of time to simply reprocess the data rather than work
out what calibration files or tools have been changed since
References on how to reprocess data in CIAO:
Analysis Guides http://cxc.harvard.edu/ciao/guides/
Data Preparation threads http://cxc.harvard.edu/ciao/threads/data.html
For the most general case, refer to the "Create a New Level=2 Event File" http://cxc.harvard.edu/ciao/threads/createL2/
Please note that although they were released at the same time,
the CIAO 3.2.1 patch does NOT require the CALDB 3.0.1 upgrade. The
two releases function independently. See the release notes for
CIAO and CALDB are available for download from: http://cxc.harvard.edu/ciao/download/
They are also available from the European mirror site:
Elizabeth Galle and Antonella Fruscione, on behalf of the CIAO Development team