X-ray Insights into the Physics of Mini-BAL Quasar Outflows

We examine the ultraviolet and X-ray properties of 256 radio-quiet Sloan Digital Sky Survey quasars (QSOs) observed in X-rays with Chandra and/or XMM-Newton in order to study the relationship between QSOs with broad C IV absorption lines (BALs; width >2000 km s-1) and those with C IV mini-BALs (h...

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Bibliographic Details
Published in:The Astrophysical journal 2009-05, Vol.696 (1), p.924-940
Main Authors: Gibson, Robert R, Brandt, W. N, Gallagher, S. C, Schneider, Donald P
Format: Article
Language:English
Subjects:
Astronomy
Earth, ocean, space
Exact sciences and technology
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Summary:We examine the ultraviolet and X-ray properties of 256 radio-quiet Sloan Digital Sky Survey quasars (QSOs) observed in X-rays with Chandra and/or XMM-Newton in order to study the relationship between QSOs with broad C IV absorption lines (BALs; width >2000 km s-1) and those with C IV mini-BALs (here defined to have widths of 1000-2000 km s-1). Our sample includes 42 BAL and 48 mini-BAL QSOs. The relative X-ray brightness and hard spectral slopes of the mini-BAL population are, on average, intermediate between those of BAL and non-BAL QSOs, as might be expected if narrower and broader absorption line outflows are physically related. However, a significant population of mini-BALs has outflow velocities higher than would be expected for BAL QSOs of the same relative X-ray brightness. Consistently strong X-ray absorption is apparently not required to accelerate at least some mini-BALs to high outflow velocities. Assuming the mini-BAL features are correctly attributed to intrinsic C IV absorption, we suggest that their observed properties may be explained if mini-BALs are 'seeds' that can be accelerated to form BALs when sufficient X-ray shielding is present. We also examine several QSOs with broad C IV absorption that have been recently reported to be unusually X-ray bright. Such cases are frequently mini-BAL QSOs, which, as a population, are generally brighter in X-rays than BAL QSOs. Pointed XMM-Newton observations also suggest that these sources (or unresolved neighbors) may have been previously observed in a high-flux state.
ISSN:0004-637X
1538-4357
DOI:10.1088/0004-637X/696/1/924