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Title:
Are Optically Selected Quasars Universally X-Ray Luminous? X-Ray-UV Relations in Sloan Digital Sky Survey Quasars
Authors:
Gibson, Robert R.; Brandt, W. N.; Schneider, Donald P.
Affiliation:
AA(Department of Astronomy and Astrophysics, 525 Davey Laboratory, Pennsylvania State University, University Park, PA 16802; ), AB(Department of Astronomy and Astrophysics, 525 Davey Laboratory, Pennsylvania State University, University Park, PA 16802; ), AC(Department of Astronomy and Astrophysics, 525 Davey Laboratory, Pennsylvania State University, University Park, PA 16802; )
Publication:
The Astrophysical Journal, Volume 685, Issue 2, pp. 773-786. (ApJ Homepage)
Publication Date:
10/2008
Origin:
UCP
ApJ Keywords:
Galaxies: Active, Galaxies: Nuclei, Galaxies: Quasars: Absorption Lines, Galaxies: Quasars: Emission Lines, X-Rays: General
DOI:
10.1086/590403
Bibliographic Code:
2008ApJ...685..773G

Abstract

We analyze archived Chandra and XMM-Newton X-ray observations of 536 Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5) quasars (QSOs) at 1.7<=z<=2.7 in order to characterize the relative UV and X-ray spectral properties of QSOs that do not have broad UV absorption lines (BALs). We constrain the fraction of X-ray-weak, non-BAL QSOs and find that such objects are rare; for example, sources underluminous by a factor of 10 comprise <~2% of optically selected SDSS QSOs. X-ray luminosities vary with respect to UV emission by a factor of <~2 over several years for most sources. UV continuum reddening and the presence of narrow-line absorbing systems are not strongly associated with X-ray weakness in our sample. X-ray brightness is significantly correlated with UV emission-line properties, so that relatively X-ray-weak, non-BAL QSOs generally have weaker, blueshifted C IV λ1549 emission and broader C III] λ1909 lines. The C IV emission-line strength depends on both UV and X-ray luminosity, suggesting that the physical mechanism driving the global Baldwin effect is also associated with X-ray emission.
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