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Last modified: 2 July 2019


Catalog Release Views and Current Database Views

Since Chandra is an on-going mission, new observations are continually becoming public, and from time to time these will be processed through the CSC pipelines with the aim of producing a new catalog release. To distinguish between stable catalog versions and source and detection information extracted from observations currently undergoing catalog processing, there are two ways of viewing the CSC: catalog release views and current database view.

Catalog Release View

A catalog release view is a carefully reviewed, static version of the CSC, that will never change, even if newly available data alter our knowledge about a source. These views are appropriate for the user who requires a stable, validated catalog or detailed characterization of the statistical properties of the catalog, such as limiting sensitivity, completeness, false source rates, astrometric and photometric accuracy, and variability information. To be included in a catalog release view, a detection must meet the significance requirements of the specific catalog release. For example, to be included in CSC release 1 a detection must have a flux significance of 3.0σ or greater in at least one science energy band in a single observation. For CSC release 2 a more complex instrument- and theta-dependent likelihood-based threshold is applied. All catalog release views (including those prior to the most current) will remain available to the end-user indefinitely.

Once a name is assigned to a source in a catalog release view, the name remains frozen for all catalog releases with the same major version (e.g., CSC 1.x or CSC 2.x). In other words, for all catalog releases with the same major version number the source will retain its originally assigned name, even if the most up-to-date information about that source renders its name incorrect based on updated knowledge of the source position. A source named in the current catalog release view may be removed from subsequent catalog release views; this could occur if the source does not meet the significance or quality assurance criteria of the new catalog release, or if new observations determine that the original 'source' is in fact a (previously unresolved) group of sources. Source names are not guaranteed to remain the same if the major catalog version number is changed, although if a change is made then the catalog prefix designation will be updated (e.g., from CXO to 2CXO).

The data from an ongoing processing are made available in the current database view, described below, and will ultimately be reflected in the next catalog release view.

Current Database View

When production of a new version of the catalog is underway, the current database view provides direct access to the active CSC databases as they exist at the time of query submission. This view includes the most recently processed datasets which have not yet been included in a catalog release view. A source must meet the significance requirements of the upcoming catalog release to be included in the database view. The catalog databases will be updated continually as observations are processed.

During catalog production, users who wish to search the latest data (e.g., to identify sources with specific signatures for follow-up studies), may prefer to do so using the current database view. However, since the current database view is dynamic, reported source and detection properties and data products may be superseded at any time without notice, and sources/detections may even be removed by subsequent quality assurance analyses. The statistical properties of data in the current database view are not guaranteed.