We present a catalog of Chandra Source Catalog 2.0 sources cross-matched with SDSS DR15/16 counterparts. The crossmatch is performed with a Bayesian method developed by Budavari & Szalay (2008ApJ...679..301B) as implemented and extended by A. Rots (2020, https://cxc.cfa.harvard.edu/cda/files/XmatchQuickSummary.pdf) that takes into account local source density as well as both error ellipses and raw-size ellipses of the sources (for more details, see https://cxc.cfa.harvard.edu/cda/files/XmatchQuickSummary.pdf). CSC2.0 sources are extracted from the CSC2.0 "Master Source" table (https://cxc.harvard.edu/csc/columns/master_alpha.html), while SDSS DR15 are from the "Star" or "Galaxy" views. For each crossmatched source pair the match probability, match type and match grade are provided. In addition, ambiguous matches are explicitly called out and provided in separate published tables. The lists of ambiguous matches can be found in the following files: https://cxc.cfa.harvard.edu/cda/files/CSC2-SDSSDR15SG_AmbiguousXmatch.txt https://cxc.cfa.harvard.edu/cda/files/SDSSDR15SG-CSC2_AmbiguousXmatch.txt and a simple readme file is located at: https://cxc.cfa.harvard.edu/cda/files/AmbiguousXmatch.readme

Cone search capability for table IX/62/catalog (CSC2-SDSSDR15 crossmatch catalog)