TY - JOUR
T1 - The Frequency of Intrinsic X-Ray Weakness among Broad Absorption Line Quasars
AU - Liu, Hezhen
AU - Luo, B.
AU - Brandt, W. N.
AU - Gallagher, S. C.
AU - Garmire, G. P.
N1 - Funding Information:
We thank the referee for reviewing the manuscript carefully and providing helpful comments. We thank YongShi, QiushengGu, PengWei, ChenHu, and PuDu for helpful discussions. We acknowledge financial support from the National Natural Science Foundation of China grant 11673010 (H.L., B.L.), National Key R&D Program of China grant 2016YFA0400702 (H.L., B.L.), and the National Thousand Young Talents program of China (B.L.). W.N.B. acknowledges support from Chandra X-ray Center grant GO5-16089X, the NASA ADP Program, and the Penn State ACIS Instrument Team Contract SV4-74018 (issued by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of NASA under contract NAS8-03060). S.C.G. thanks the Discovery Grant Program of the Natural Science and Engineering Research Council of Canada.
Publisher Copyright:
© 2018. The American Astronomical Society. All rights reserved.
PY - 2018/6/1
Y1 - 2018/6/1
N2 - We present combined ≈14-37 ks Chandra observations of seven z = 1.6-2.7 broad absorption line (BAL) quasars selected from the Large Bright Quasar Survey (LBQS). These seven objects are high-ionization BAL (HiBAL) quasars, and they were undetected in the Chandra hard band (2-8 keV) in previous observations. The stacking analyses of previous Chandra observations suggested that these seven objects likely contain some candidates for intrinsically X-ray weak BAL quasars. With the new Chandra observations, six targets are detected. We calculate their effective power-law photon indices and hard-band flux weakness, and find that two objects, LBQS 1203+1530 and LBQS 1442-0011, show soft/steep spectral shapes ( and ) and significant X-ray weakness in the hard band (by factors of ≈15 and 12). We conclude that the two HiBAL quasars are good candidates for intrinsically X-ray weak BAL quasars. The mid-infrared-to-ultraviolet spectral energy distributions of the two candidates are consistent with those of typical quasars. We constrain the fraction of intrinsically X-ray weak active galactic nuclei (AGNs) among HiBAL quasars to be ≈7%-10% (2/29-3/29), and we estimate it is ≈6%-23% (2/35-8/35) among the general BAL quasar population. Such a fraction is considerably larger than that among non-BAL quasars, and we suggest that intrinsically X-ray weak quasars are preferentially observed as BAL quasars. Intrinsically X-ray weak AGNs likely comprise a small minority of the luminous type 1 AGN population, and they should not affect significantly the completeness of these AGNs found in deep X-ray surveys.
AB - We present combined ≈14-37 ks Chandra observations of seven z = 1.6-2.7 broad absorption line (BAL) quasars selected from the Large Bright Quasar Survey (LBQS). These seven objects are high-ionization BAL (HiBAL) quasars, and they were undetected in the Chandra hard band (2-8 keV) in previous observations. The stacking analyses of previous Chandra observations suggested that these seven objects likely contain some candidates for intrinsically X-ray weak BAL quasars. With the new Chandra observations, six targets are detected. We calculate their effective power-law photon indices and hard-band flux weakness, and find that two objects, LBQS 1203+1530 and LBQS 1442-0011, show soft/steep spectral shapes ( and ) and significant X-ray weakness in the hard band (by factors of ≈15 and 12). We conclude that the two HiBAL quasars are good candidates for intrinsically X-ray weak BAL quasars. The mid-infrared-to-ultraviolet spectral energy distributions of the two candidates are consistent with those of typical quasars. We constrain the fraction of intrinsically X-ray weak active galactic nuclei (AGNs) among HiBAL quasars to be ≈7%-10% (2/29-3/29), and we estimate it is ≈6%-23% (2/35-8/35) among the general BAL quasar population. Such a fraction is considerably larger than that among non-BAL quasars, and we suggest that intrinsically X-ray weak quasars are preferentially observed as BAL quasars. Intrinsically X-ray weak AGNs likely comprise a small minority of the luminous type 1 AGN population, and they should not affect significantly the completeness of these AGNs found in deep X-ray surveys.
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U2 - 10.3847/1538-4357/aabe8d
DO - 10.3847/1538-4357/aabe8d
M3 - Article
AN - SCOPUS:85048321790
VL - 859
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 2
M1 - 113
ER -