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Register a new userThe Correlation between X-ray and UV Properties of BAL QSOs
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We compile a large sample of broad absorption lines (BAL) quasars with X-ray observations from the xmm archive data and Sloan Digital Sky Survey Data Release 5. The sample consists of 41 BAL QSOs. Among 26 BAL quasars detected in X-ray, spectral analysis is possible for twelve objects. X-ray absorption is detected in all of them. Complementary to that of citet{gall06} (thereafter G06), our sample spans wide ranges of both BALnicity Index (BI) and maximum outflow velocity (vmax). Combining our sample with G06s, we find very significant correlations between the intrinsic X-ray weakness with both BALnicity Index (BI) and the maximum velocity of absorption trough. We do not confirm the previous claimed correlation between absorption column density and broad absorption line parameters. We tentatively interpret this as that X-ray absorption is necessary to the production of the BAL outflow, but the properties of the outflow are largely determined by intrinsic SED of the quasars.
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We report on an X-ray and optical/UV study of eight Broad Absorption Line (BAL) to non-BAL transforming quasars at $z,approx,$1.7-2.2 over 0.29-4.95 rest-frame years with at least three spectroscopic epochs for each quasar from the SDSS, BOSS, $Gemini$, and ARC 3.5-m telescopes. New $Chandra$ observations obtained for these objects show their values of $alpha_{rm ox}$ and $Delta{alpha}_{rm ox}$, as well as their spectral energy distributions, are consistent with those of non-BAL quasars. Moreover, our targets have X-ray spectral shapes that are, on average, consistent with weakened absorption with an effective power-law photon index of $Gamma_{rm eff},=,1.69^{+0.25}_{-0.25}$. The newer $Gemini$ and ARC 3.5-m spectra reveal that the BAL troughs have remained absent since the BOSS observations where the BAL disappearance was discovered. The X-ray and optical/UV results in tandem are consistent with at least the X-ray absorbing material moving out of the line-of-sight, leaving an X-ray unabsorbed non-BAL quasar. The UV absorber might have become more highly ionized (in a shielding-gas scenario) or also moved out of the line-of-sight (in a wind-clumping scenario).
We have embarked upon a project to model the UV spectra of BALQSOs using a Monte Carlo radiative transfer code previously validated through modelling of the winds of cataclysmic variable stars (e.g. Noebauer et al. 2010). We intend to use the simulations to investigate the plausibility of geometric unification (e.g. Elvis 2000) of the different classes of QSO. Here we introduce the code, and present some initial results. These demonstrate that for reasonable geometries and mass loss rates we are able to produce synthetic spectra which reproduce the important features of observed BALQSO spectra.
We investigated the rest-frame $approx$0.1-5 year X-ray variability properties of an unbiased and uniformly selected sample of 24 BAL and 35 mini-BAL quasars, making it the largest representative sample used to investigate such variability. We find that the distributions of X-ray variability amplitudes of these quasar populations are statistically similar to that of non-BAL, radio-quiet (typical) quasars.
The UV spectra of Galactic and extragalactic sightlines often show OVI absorption lines at a range of redshifts, and from a variety of sources from the Galactic circumgalactic medium to AGN outflows. Inner shell OVI absorption is also observed in X-ray spectra (at lambda=22.03 AA), but the column density inferred from the X-ray line was consistently larger than that from the UV line. Here we present a solution to this discrepancy for the z=0 systems. The OII K-beta line ^4S^0 --> (^3D)3p ^4P at 562.40 eV (==22.04 AA) is blended with the OVI K-alpha line in X-ray spectra. We estimate the strength of this OII line in two different ways and show that in most cases the OII line accounts for the entire blended line. The small amount of OVI equivalent width present in some cases has column density entirely consistent with the UV value. This solution to the OVI discrepancy, however, does not apply to the high column density systems like AGN outflows. We discuss other possible causes to explain their UV/X-ray mismatch. The OVI and OII lines will be resolved by gratings on-board the proposed mission Arcus and the concept mission Lynx and would allow detection of weak OVI lines not just at z=0 but also at higher redshift.
The variability of quasars across multiple wavelengths is a useful probe of physical conditions in active galactic nuclei. In particular, variable accretion rates, instabilities, and reverberation effects in the accretion disk of a supermassive black hole (SMBH) are expected to produce correlated flux variations in UV and optical bands. Recent work has further argued that binary quasars should exhibit strongly correlated UV and optical periodicities. Strong UV-optical correlations have indeed been established in small samples of up to approximately 30 quasars with well-sampled light curves, and have extended the bluer-when-brighter trend previously found within the optical bands. Here we further test the nature of quasar variability by examining the observed-frame UV-optical correlations in a large sample of 1,315 bright quasars with overlapping UV and optical light curves for the Galaxy Evolution Explorer (GALEX) and the Catalina Real-time Transient Survey (CRTS), respectively. We find that strong correlations exist in this much larger sample, but we rule out, at approximately 95% confidence, the simple hypothesis that the intrinsic UV and optical variations of all quasars are fully correlated. Our results therefore imply the existence of physical mechanism(s) that can generate uncorrelated optical and UV flux variations.
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