{
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  "accessLevel": "public",
  "bureauCode": [
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  "contactPoint": {
    "@type": "vcard:Contact",
    "fn": "HEASARC Help Desk",
    "hasEmail": "mailto:andrew.ptak@nasa.gov"
  },
  "description": "The Nonparametric Bayes Classifier (NBC) Quasar Candidate Catalog is a catalog of 100,563 unresolved, UV-excess (UVX) quasar candidates with magnitudes to as faint as 21 in the g-band from 2099 square degrees of the Sloan Digital Sky Survey (SDSS) Data Release One (DR1) imaging data. Existing spectra of 22,737 sources reveals that 22,191 (97.6%) are quasars; accounting for the magnitude dependence of this efficiency, the authors estimate that 95,502 (95.0%) of the objects in the catalog are quasars. Such a high efficiency is unprecedented in broadband surveys of quasars. This "proof-of-concept" sample is designed to be maximally efficient, but still has 94.7% completeness to unresolved, g ~< 19.5, UVX quasars from the DR1 quasar catalog. This efficient and complete selection is the result of the application of a probability density type analysis to training sets that describe the four-dimensional color distribution of stars and spectroscopically confirmed quasars in the SDSS. Specifically, the authors use a nonparametric Bayesian classification, based on kernel density estimation, to parametrize the color distribution of astronomical sources - allowing for fast and robust classification. They further supplement the catalog by providing photometric redshifts and matches to FIRST/VLA, ROSAT, and USNO-B sources. Much more information on the SDSS is available at the project's web site at <a href=\"http://www.sdss.org/\">http://www.sdss.org/</a>. This database table was created by the HEASARC in August 2005 based on CDS table J/ApJS/155/257/table1.dat. This is a service provided by NASA HEASARC .",
  "distribution": [
    {
      "@type": "dcat:Distribution",
      "downloadURL": "https://heasarc.gsfc.nasa.gov/W3Browse/all/sdssnbcqsc.html",
      "format": "HTML",
      "mediaType": "text/html"
    },
    {
      "@type": "dcat:Distribution",
      "downloadURL": "https://heasarc.gsfc.nasa.gov/xamin/vo/cone?showoffsets&table=sdssnbcqsc&",
      "format": "BIN",
      "mediaType": "application/octet-stream"
    }
  ],
  "identifier": "ivo://nasa.heasarc/sdssnbcqsc",
  "keyword": [
    "__"
  ],
  "landingPage": "ivo://nasa.heasarc/sdssnbcqsc",
  "license": "https://www.usa.gov/government-works",
  "modified": "2026-09-07",
  "programCode": [
    "026:000"
  ],
  "publisher": {
    "@type": "org:Organization",
    "name": "High Energy Astrophysics Science Archive Research Center"
  },
  "theme": [
    "Astrophysics"
  ],
  "title": "Sloan Digital Sky Survey NBC Quasar Candidate Catalog"
}