The XMM-Newton View of Weak Emission-Line Quasars
Abstract
The Sloan Digital Sky Survey discovered a remarkable set of quasars at z = 2.2 - 5.9 having extremely weak rest-frame UV emission lines in their spectra (hereafter, WLQs). One hypothesis explaining the extreme weakness of their emission lines is that WLQs are high accretion rate sources, and one manifestation of a high accretion rate is a steep hard-X-ray spectral slope. We therefore performed spectral analysis of all the high-quality X-ray observations of WLQs available in the archive. This analysis includes new XMM-Newton observations of SDSS J0928+1848 and SDSS J1231+0138, at z = 3.8 and z = 3.2 respectively, alongside the spectral analysis of two archival XMM-Newton sources, SDSS J1141+0219 and SDSS J1012+5313, at z = 3.6 and z = 3.0 respectively. With a total exposure time of ∼78 ks and an average of ∼1200 counts per source, we derived the hard-X-ray photon index for each object, as well as the mean photon index derived from joint-fitting these spectra, while accounting for the possibility of intrinsic absorption for which we found no evidence. Our results show that the mean photon index of the four WLQs is below the average observed in luminous radio-quiet quasars, consistent with the fact that all of the WLQs in the XMM-Newton archive are radio intermediate. This is mainly a consequence of selecting the X-ray brightest WLQs for XMM-Newton observations. In order to be able to test the hypothesis that WLQs have high accretion rates, future XMM-Newton observations should target radio-quiet WLQs, and suitable candidates likely lie at lower redshifts, i.e. at z < 2.2.
- Publication:
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American Astronomical Society Meeting Abstracts #223
- Pub Date:
- January 2014
- Bibcode:
- 2014AAS...22315002S