TY - JOUR
T1 - Are optically selected quasars universally X-ray luminous? X-ray-UV relations in Sloan digital sky survey quasars
AU - Gibson, Robert R.
AU - Brandt, W. N.
AU - Schneider, Donald P.
PY - 2008/10/1
Y1 - 2008/10/1
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=53549097043&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=53549097043&partnerID=8YFLogxK
U2 - 10.1086/590403
DO - 10.1086/590403
M3 - Article
AN - SCOPUS:53549097043
SN - 0004-637X
VL - 685
SP - 773
EP - 786
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
ER -