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Last modified: 26 September 2006

URL: http://cxc.harvard.edu/ciao3.4/data/basics.html
Hardcopy (PDF): A4 | Letter

Data Products Basics

There are several fundamental points that all users should be aware of when analyzing Chandra data:

File Formats

All CXC data products are in FITS format and are consistent with OGIP standards. The exceptions are the images and plots (JPEG format) and the summary pages (HTML format).

Software Versions

These products were created by the pipeline, which is outlined on the Standard Data Processing page. The pipeline is constantly updated; check the Release Notes for the newest changes, which are organized by software version (ASCDSVER). The Note on Processing Versions thread gives an example of how to check this header keyword.


The calibration files used in processing, as well as those needed for data analysis, are kept in the calibration database (CALDB). Like Chandra data, all the files are in OGIP FITS standard formats.

"Most Wanted" Files

The files used most frequently in data analysis are all contained in the "primary products" of the distribution. "Secondary products" are occasionally useful for specialized analysis needs (e.g. barycenter-correcting event times requires the orbit ephemeris files); this is noted in the documentation when applicable.

The Introduction to the Data Products thread describes all the Chandra data products in detail. There are many other CIAO Science Threads which provide instructions on how to accomplish many useful analysis tasks.

Hardcopy (PDF): A4 | Letter
Last modified: 26 September 2006

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