Chandra Publication Statistics

In this study we develop and propose publication metrics, based on an analysis of data from the Chandra bibliographic database, that are more meaningful and less sensitive to observatory-specific characteristics than the traditional metrics. They fall in three main categories: speed of publication; fraction of observing time published; and archival usage. Citation of results is a fourth category, but lends itself less well to definite statements. For Chandra, the median time from observation to publication is 2.36 years; after about 7 years 90% of the observing time is published; after 10 years 70% of the observing time is published more than twice; and the total annual publication output of the mission is 60-70% of the cumulative observing time available, assuming a two year lag between data retrieval and publication.Comment: 22 pages, 8 figures, 3 tables; revised manuscript submitted to PAS

The High Impact of Astronomical Data Archives

Archives are widely recognized as a valuable resource for astronomy, but statistics on their use indicates they are even more important than most astronomers realize. Obviously much of the science from survey projects such as SDSS relies on the archive. Perhaps more surprisingly, archival data are also a major contributor to the science from targeted, PI-driven missions such as HST, Chandra, Spitzer and the ground-based observatories. Archival research currently accounts for half of the ~1200 Hubble and Chandra science papers published each year, and the use of the archive continues to increase. The archival data products are, in the long term, as important as the PI science programs. It is vital to recognize the large impact archives can have on the science generated by missions and observatories. The value of the archive should be an important factor in the establishment of new projects. Future missions and observatories should not only budget adequate resources to support a robust archive, but they also should consider the effects of mission design and operations decisions on the archive. Additional funding both for archive users and archive centers -- particularly with an eye to enabling cross-archive, multiwavelength science -- is a relatively inexpensive way to increase the science output from our major investments in large projects

The Chandra Source Catalog

The Chandra Source Catalog (CSC) is a general purpose virtual X-ray astrophysics facility that provides access to a carefully selected set of generally useful quantities for individual X-ray sources, and is designed 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. The first release of the CSC includes information about 94,676 distinct X-ray sources detected in a subset of public ACIS imaging observations from roughly the first eight years of the Chandra mission. This release of the catalog includes point and compact sources with observed spatial extents <~ 30''. The catalog (1) provides access to the best estimates of the X-ray source properties for detected sources, with good scientific fidelity, and directly supports scientific analysis using the individual source data; (2) facilitates analysis of a wide range of statistical properties for classes of X-ray sources; and (3) provides efficient access to calibrated observational data and ancillary data products for individual X-ray sources, so that users can perform detailed further analysis using existing tools. The catalog includes real X-ray sources detected with flux estimates that are at least 3 times their estimated 1 sigma uncertainties in at least one energy band, while maintaining the number of spurious sources at a level of <~ 1 false source per field for a 100 ks observation. For each detected source, the CSC provides commonly tabulated quantities, including source position, extent, multi-band fluxes, hardness ratios, and variability statistics, derived from the observations in which the source is detected. In addition to these traditional catalog elements, for each X-ray source the CSC includes an extensive set of file-based data products that can be manipulated interactively.Comment: To appear in The Astrophysical Journal Supplement Series, 53 pages, 27 figure

Statistical Characterization of the Chandra Source Catalog

The first release of the Chandra Source Catalog (CSC) contains ~95,000 X-ray sources in a total area of ~0.75% of the entire sky, using data from ~3,900 separate ACIS observations of a multitude of different types of X-ray sources. In order to maximize the scientific benefit of such a large, heterogeneous data-set, careful characterization of the statistical properties of the catalog, i.e., completeness, sensitivity, false source rate, and accuracy of source properties, is required. Characterization efforts of other, large Chandra catalogs, such as the ChaMP Point Source Catalog (Kim et al. 2007) or the 2 Mega-second Deep Field Surveys (Alexander et al. 2003), while informative, cannot serve this purpose, since the CSC analysis procedures are significantly different and the range of allowable data is much less restrictive. We describe here the characterization process for the CSC. This process includes both a comparison of real CSC results with those of other, deeper Chandra catalogs of the same targets and extensive simulations of blank-sky and point source populations.Comment: To be published in the Astrophysical Journal Supplement Series (Fig. 52 replaced with a version which astro-ph can convert to PDF without issues.