Connecting the X-ray properties of weak-line and typical quasars: testing for a geometrically thick accretion disk
| Autor: | Ni, Qingling, Brandt, W. N., Luo, B., Hall, P. B., Shen, Yue, Anderson, S. F., Plotkin, R. M., Richards, Gordon T., Schneider, D. P., Shemmer, O., Wu, J. |
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| Rok vydání: | 2018 |
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| Druh dokumentu: | Working Paper |
| DOI: | 10.1093/mnras/sty1989 |
| Popis: | 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. Comment: 21 pages, 12 figures. Accepted for publication in MNRAS |
| Databáze: | arXiv |
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