Building Release 2 of the Chandra Source Catalog

摘要

The second major release of the Chandra Source Catalog builds on the first catalog release by stacking subsets of overlapping observations, using a permissive source detection approach to identify source candidates and enable point detections down to ~ 5 net counts on-axis, and evaluating the reality of the candidate detections by applying a Sherpa-based maximum-likelihood estimator.?The catalog provides a detailed set of properties for each X-ray source, including source position, extent, multi-band aperture photometry, spectral fits and hardness ratios, and temporal variability measures. In addition, the catalog provides per-field and per-source data products such as images, photon event lists, spectra, light curves, and extended source polygons. We highlight the differences between the first and second catalog releases, and discuss the decisions that drove the changes. We present the newly developed techniques that were required to build release 2 of the catalog, and identify algorithms that have been updated. Finally, we briefly discuss lessons learned.