Chandra Source Catalog

Ian N. Evans for the Chandra Source Catalog team

Catalog development has continued on the Chandra Source Catalog (CSC) since the last major release, version 2.1 (CSC 2.1) on April 2, 2024, albeit at a slower pace. CSC 2.1 provides uniformly processed tabulated positional, spatial, photometric, spectral, and temporal source properties, as well as roughly forty types of science-ready X-ray data products, for ACIS and HRC-I imaging observations released publicly prior to the end of 2021. The catalog includes measured and derived properties for 407,806 unique compact and extended X-ray sources in the sky, and extracted properties are provided for 1,304,376 individual observation detections (2,143,847 including photometric upper limits). All coordinates are tied to the Gaia-CRF3 realization of the International Celestial Reference Frame for the best possible astrometry for catalog sources.

The only catalog update since the CSC 2.1 release was a minor overlay release, CSC 2.1.1, which occurred on October 18, 2024. This release corrected four issues identified in CSC 2.1 but did not otherwise add any new datasets to the catalog. The two main updates included in CSC 2.1.1 were correcting the names of 400 X-ray sources that had been previously identified and published and populating aperture photometry and derived properties that were inadvertently set to NULL in CSC 2.1 for ~7,000 sources—mostly in the vicinity of the Galactic center.

Also, during this period, a paper describing CSC 2.0 and 2.1 was published in The Astrophysical Journal Supplement Series. This paper, Ian N. Evans et al. (2024 ApJS 274 22; doi:10.3847/1538-4365/ad6319), describes the content of the catalog and is the best reference for the algorithms used to construct the CSC.

As always, access to both the catalog data and documentation is available through the catalog website (https://cxc.cfa.harvard.edu/csc/index.html). The catalog documentation describes the content and organization of the catalog data, explains the data processing steps, and includes detailed descriptions of the tabulated source and detection properties and data products. We suggest reviewing the Catalog Organization & Concepts page to make the most effective use of the catalog. Additionally, the Caveats and Limitations page provides important information about the catalog that should be reviewed by all researchers prior to using the catalog data. Multiple user interfaces to the catalog are accessible via the catalog website's How to Access the CSC page.

More recently, we have started production processing of the next catalog release, CSC 2.2. Like CSC 2.1, release 2.2 will be an incremental release, this time adding ACIS and HRC-I imaging observations released publicly in 2022 and 2023 to the content of CSC 2.1. The decision to limit CSC 2.2 to include only an additional two years of observations was made to ensure that catalog processing could be completed within the current fiscal year given the uncertain funding environment going forward. CSC 2.2 otherwise will be unchanged from CSC 2.1, with one very minor exception: the release will include a new aperture photometry MCMC draws science-ready data product. These were previously produced internally to create the existing Bayesian X-ray aperture photometry marginalized posterior probability density functions, but we will be making them available publicly based on requests from catalog science users.

Based on simple scaling, CSC 2.2 is expected to add about forty thousand new sources to the catalog; however, because new observations are being added to previously observed fields, the total number of sources with properties that will be updated is very roughly two times larger.