The Quasars.org (QORG) Catalog is an all-sky optical catalog of radio/X-ray sources. The QORG Catalog aligns and overlays the year 2001/2 releases of the ROSAT HRI, RASS, PSPC and WGA X-ray catalogs, the NVSS (2002), FIRST (2003) and SUMSS (2003) radio catalogs, the Veron QSO catalog (2003) and various galaxy/star reference catalogs onto the optical APM and USNO-A catalogs. This catalog displays calculated percentage probabilities for each optical, radio/X-ray associated object of its likelihood of being a quasar, galaxy, star, or erroneous radio/X-ray association. This table contains the main Master QORG catalog (master.dat) and contains all 501,756 radio/X-ray associated optical objects and known quasars which are optically detected in APM/USNO-A. Up to six radio/X-ray catalog identifications are presented for each optical object, plus any double radio lobes (21,498 of these). These are superimposed (and laterally fitted) onto a 670,925,779-object optical background which combines APM and USNO-A data. Other subsets of this master catalog are available at the CDS, including the Free-Lunch catalog, a concise easy-to-read variant of the Master catalog showcasing just one X-ray and/or radio identification for each object, a subset catalog of QSO candidates, and a subset catalog of known QSOs/galaxies/stars. Objects presented in this catalog are those optical APM/USNO-A objects which are associated with X-ray/radio detections, or any optically-found catalogued QSO/AGN/Bl Lac objects, which have confidence levels >40% of being radio/X-ray emitting optical objects. There are 501,756 objects included in all (including 48,285 catalogued quasars), representing the 99.4% coverage of the sky which is available from the APM and USNO-A. Each object is shown as one entry giving the position in equatorial coordinates, red and blue optical magnitudes (recalibrated) and PSF class, calculated probabilities of the object being, separately, a quasar, galaxy, star, or erroneous radio/X-ray association, any radio identification from each of the NVSS, FIRST and SUMSS surveys, including candidate double-lobe detections, any X-ray identification from each of the ROSAT HRI, RASS, PSPC and WGA surveys, including fluxes and field shifts of those identifications, plus, if already catalogued, the object name and redshift where applicable. The QORG catalog and supporting data can be accessed from the catalog home page at <a href="http://quasars.org/qorg-data.htm">http://quasars.org/qorg-data.htm</a> Questions or comments on the catalog contents may be directed to the first author Eric Flesch at eric@flesch.org. The authors request that researchers using this catalog make a small acknowledgement of such use in any published papers which thereby result. This table was created by the HEASARC in November 2004 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/A+A/427/387">CDS Catalog J/A+A/427/387</a> file master.dat.gz. This is a service provided by NASA HEASARC .
