ROSAT observations of z>3 quasars

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16 Scopus citations


Successful pointed observations using the ROSAT PSPC were made of seven z>3 optically selected quasars from the Large Bright Quasar Survey (LBQS). Four detections and three 3σ upper limits resulted. Combining these data with the heterogeneous sample of Avni & Tananbaum [ApJ, 305, 83 (1986)] confirms their conclusion that the ratio of x-ray to optical luminosity is correlated with optical luminosity and probably not correlated with redshift. This suggests that x-ray luminosity evolves more slowly than optical luminosity. These results are then used in conjunction with the LBQS database to estimate the contribution to the 2 keV x-ray background of bright, optically selected quasars with mBJ < 18.85; the result is about 5%.

Original languageEnglish (US)
Pages (from-to)1542-1547
Number of pages6
JournalAstronomical Journal
Issue number5
StatePublished - Nov 1994

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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