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Connecting the X-ray properties of weak-line and typical quasars: testing for a geometrically thick accretion disk
Monthly notices of the Royal Astronomical Society, v 480(4), pp 5184-5202
23 Jul 2018
Abstract
We present X-ray and multiwavelength analyses of 32 weak emission-line quasars (WLQs) selected in a consistent and unbiased manner. New $Chandra$ 3.1-4.8 ks observations were obtained for 14 of these WLQs with C IV rest-frame equivalent widths (REWs) of 5-15 \r{A}, and these serve as an X-ray observational "bridge" between previously studied WLQs with C IV REW $\lesssim$ 5 \r{A} and more-typical quasars with C IV REW $\approx$ 15-100 \r{A}. We have identified and quantified a strong dependence of the fraction of X-ray weak quasars upon C IV REW; this fraction declines by a factor of $\approx 13$ (from $\approx 44$% to $\approx 3$%) for C IV REW ranging from 4-50 \r{A}, and the rate of decline appears particularly strong in the 10-20 \r{A} range. The dependence broadly supports the proposed "shielding" model for WLQs, in which a geometrically and optically thick inner accretion disk, expected for a quasar accreting at a high Eddington ratio, both prevents ionizing EUV/X-ray photons from reaching the high-ionization broad emission-line region and also sometimes blocks the line-of-sight to the central X-ray emitting region. This model is also supported by the hard average spectral shape of X-ray weak WLQs (with a power-law effective photon index of $\Gamma_{\rm eff}=1.19^{+0.56}_{-0.45}$). Additionally, we have examined UV continuum/emission-line properties that might trace X-ray weakness among WLQs, confirming that red UV continuum color is the most-effective tracer.
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Details
- Title
- Connecting the X-ray properties of weak-line and typical quasars: testing for a geometrically thick accretion disk
- Creators
- Qingling Ni - Pennsylvania State UniversityW. N. Brandt - Pennsylvania State UniversityB. Luo - Nanjing UniversityP. B. Hall - York UniversityYue Shen - University of Illinois Urbana-ChampaignS. F. Anderson - University of WashingtonR. M. Plotkin - International Centre for Radio Astronomy ResearchGordon T. Richards - Drexel UniversityD. P. Schneider - Pennsylvania State UniversityO. Shemmer - University of North TexasJ. Wu - Xiamen University
- Publication Details
- Monthly notices of the Royal Astronomical Society, v 480(4), pp 5184-5202
- Publisher
- Oxford University Press
- Grant note
- 1715579 / National Science Foundation (nsf_________::NSF) unidentified / Natural Sciences and Engineering Research Council of Canada (nserc_______::NSERC)
- Resource Type
- Other
- Language
- English
- Academic Unit
- Physics
- Web of Science ID
- WOS:000449617100072
- Scopus ID
- 2-s2.0-85104504331
- Other Identifier
- 991019168908404721
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- Collaboration types
- Domestic collaboration
- International collaboration
- Web of Science research areas
- Astronomy & Astrophysics