Data Products Basics
The Chandra X-ray Center (CXC) produces a set of standard data products for every Chandra observation. As soon as the data are processed, these products are made available to the principal investigator (PI) and the designated observer on the proposal. After one year (sometimes sooner), the data are made public in the Chandra Data Archive, and so are available to anyone to analyze.
There are several fundamental points that all users should be aware of when analyzing Chandra data:
- File Formats
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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
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The data products are created by the standard data processing pipeline, which is outlined in the Standard Data Processing dictionary entry. As the pipeline is often updated, it is useful to know which version of the processing software was used to create your dataset. The software version is stored in the ASCDSVER header keyword; the Note on Processing Versions thread gives an example of how to check the keyword.
- Calibration
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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.
- Standard Data Distribution
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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.