Planning and developing the Chandra Source Catalog

The Chandra Source Catalog, presently being developed by the Chandra X-ray Center, will be the definitive catalog of all X-ray sources detected by the Chandra X-ray Observatory. The catalog interface will provide users with a simple mechanism to perform advanced queries on the data content of the archival holdings on a source-by-source basis for X-ray sources matching user-specified search criteria, and is intended to satisfy the needs of a broad-based group of scientists, including those who may be less familiar with astronomical data analysis in the X-ray regime. For each detected X-ray source, the catalog will record commonly tabulated quantities that can be queried, including source position, dimensions, multi-band fluxes, hardness ratios, and variability statistics, derived from all of the observations that include the source within the field of view. However, in addition to these traditional catalog elements, for each X-ray source the catalog will include an extensive set of file-based data products that can be manipulated interactively by the catalog user, including source images, event lists, light curves, and spectra from each observation in which a source is detected. In this paper, we emphasize the design and development of the Chandra Source Catalog. We describe the evaluation process used to plan the data content of the catalog, and the selection of the tabular properties and file-based data products to be provided to the user. We discuss our approach for managing catalog updates derived from either additional data from new observations or from improvements to calibrations and/or analysis algorithms.