Are Optically-Selected Quasars Universally X-Ray Luminous? X-Ray/UV Relations in Sloan Digital Sky Survey Quasars

Aug, 2008
19 pages
Published in:
  • Astrophys.J. 685 (2008) 773
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Abstract: (arXiv)
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 \la2% of optically-selected SDSS QSOs. X-ray luminosities vary with respect to UV emission by a factor of \la2 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 CIVλ\lambda1549 emission and broader CIII]λ\lambda1909 lines. The CIV 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.