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8 April 2024
The Chandra X-ray Center is pleased to announce the availability of Release 2.1 of the Chandra Source Catalog (CSC 2.1). The catalog covers roughly 730 square degrees of sky and contains 407,806 unique X-ray sources (406,089 compact and 1,717 highly extended sources) and 1,304,376 individual source detections identified in 15,533 Chandra ACIS and HRC-I imaging observations released publicly prior to the end of 2021.
The compact source sensitivity limit for most observations is roughly 5 photons over most of the field of view, allowing us to reach the faintest sources in the X-ray sky. This is achieved by co-adding observations and using an optimized source detection approach. An updated Bayesian X-ray aperture photometry code in CSC 2.1 produces robust photometry even in crowded fields and for low count detections. Catalog astrometry is tied to the Gaia-CRF3 realization of the International Celestial Reference Frame for improved sky positions, with a systemic astrometric error of approximately 0.29 arcsec (95% confidence), which is roughly 2.5× better than the previous release.
Tabulated catalog properties for sources and detections include positions, significances, spatial extents, aperture photometry fluxes, hardness ratios, spectral model fits, and temporal variabilities, in 5 energy bands for ACIS and 1 band for HRC-I. All properties have associated independent lower and upper confidence limits. Along with tabulated data, the catalog includes roughly 40 different types of data products (e.g., spectra and responses, light curves, photometric marginalized probability density functions, extended source region polygons) for individual and co-added observation detections and sources, enabling fast scientific analysis without having to perform extensive preparatory data processing.
The catalog can be queried using multiple interfaces, including CSCview, WWT, simple web interface, and IVOA compliant services. The latter allows access from Jupyter notebooks via PyVO.