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

We examine the UV and X-ray properties of 256 radio-quiet SDSS 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) and those with C IV mini-BALs (here defined to have widths of 1000–2000 km s). 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. Consistenly 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” which 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. Subject headings: galaxies: active — galaxies: nuclei — X-rays: general — quasars: absorption lines — quasars: emission lines