An Exploratory Chandra Survey of a Well-defined Sample of 35 Large Bright Quasar Survey Broad Absorption Line Quasars

By S. C. Gallagher, W. N. Brandt, G. Chartas, R. Priddey, G. Garmire, R. Sambruna. 2006

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We present 4-7 ks Chandra observations of 35 broad absorption line (BAL) quasars from the Large Bright Quasar Survey, the largest sample of sensitive, 0.5-8.0 keV X-ray observations of this class of quasars to date. The limited ranges in both redshift (z = 1.42-2.90) and ultraviolet luminosity (a factor of ≈12) of the sample also make it relatively uniform. Of 35 targets, 27 are detected for a detection fraction of 77%, and we confirm previous studies that find BAL quasars to be generally X-ray-weak. Five of the eight nondetections are known low-ionization BAL quasars, confirming reports of extreme X-ray weakness in this subset (~10% of optically selected BAL quasars). Those BAL quasars with the hardest X-ray spectra are also the X-ray weakest, consistent with the interpretation that intrinsic absorption is the primary cause of X-ray weakness in this class of quasars as a whole. Furthermore, the observed trend is not consistent with simple neutral absorption, supporting findings from spectroscopic observations of individual targets that BAL quasars typically exhibit complex X-ray absorption (e.g., partially covering or ionized absorbers). Assuming normal quasar X-ray continua and using the hard-band (observed-frame 2-8 keV) X-ray flux to "correct" for the effects of intrinsic absorption at softer energies increases the relative X-ray to optical flux ratios to much closer to the range for normal quasars, further indicating that typically neither are high-ionization BAL quasars intrinsically X-ray-weak, nor do they suffer from Compton-thick absorption. In general, we find no evidence for correlations between X-ray weakness and ultraviolet absorption-line properties, with the exception of a likely correlation between the maximum outflow velocity of C IV absorption and the magnitude of X-ray weakness. We discuss the implications of our results for disk-wind models of BAL outflows in quasars.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/646af0a45b4fedc3454e9c8d00d3fe40b63ad173

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Citations in the corpus

The Sloan Digital Sky Survey Quasar Catalog. IV. Fifth Data Release (2007, background): “45+410125.9 is notably X-ray weak, indicating likely X-ray absorption as is often seen in BAL quasars (e.g., Gallagher et al. 2006), including those at z > 4 (Vignali et al. 2005).”
A Cosmological Framework for the Co-Evolution of Quasars, Supermassive Black Holes, and Elliptical Galaxies. II. Formation of Red Ellipticals (2007, background): “…to quasars see highly energetic (kseveral 103 km s 1) broad absorption line (BAL) outflows, and it is likely that all bright quasars exhibit some such BALs (although they may not be visible owing to geometric effects; Reichard et al. 2003; Elvis 2000; Gallagher et al. 2006; Priddey et al. 2007).”
What drives the growth of black holes (2011, background): “The maximum blueshift in BAL quasars (corresponding to the terminal velocity of the wind) is higher for sources with weaker Xray emission (e.g., Gallagher et al., 2006; Gibson et al., 2009).”
An X-ray spectral model for Compton-thick toroidal reprocessors (2009, background): “The obscuring matter in some broad-absorptionline quasars (BALs) may also be Compton-thick (e.g. Gallagher et al. 2006; Chartas et al. 2007).”
A CATALOG OF BROAD ABSORPTION LINE QUASARS IN SLOAN DIGITAL SKY SURVEY DATA RELEASE 5 (2008, methodology): “The shielding X-ray absorber may also influence other BAL properties, such as the maximum outflow velocity (e.g., Gallagher et al. 2006).”
The X-Ray Properties of the Most Luminous Quasars from the Sloan Digital Sky Survey (2007, background): “Owing to intrinsic X-ray absorption, BAL quasars also require special consideration in statistical analyses of quasar X-ray properties (e.g., Gallagher et al. 2006 and references therein).”
AGN Dusty Tori. II. Observational Implications of Clumpiness (2008, background): “Extreme cases include quasars whose optical spectrum shows little or no dust extinction while their X-ray continuum is heavily affected by Comptonthick absorption (Braito et al. 2004; Gallagher et al. 2006).”