Lens or Binary? Chandra Observations of the Wide Separation Broad Absorption Line Quasar Pair UM425

Abstract

We have obtained a 110 ksec Chandra ACIS-S exposure of UM425, a pair of QSOs at z=1.47 separated by 6.5 arcsec, which show remarkably similar emission and broad absorption line (BAL) profiles in the optical/UV. Our 5000 count X-ray spectrum of UM425A (the brighter component) is well-fit with a power law (photon spectral index Gamma=2.0) partially covered by a hydrogen column of 3.8x10^22 cm^-2. The underlying power-law slope for this object and for other recent samples of BALQSOs is typical of radio-quiet quasars, lending credence to the hypothesis that BALs exist in every quasar. Assuming the same Gamma for the much fainter image of UM425B, we detect an obscuring column 5 times larger. We search for evidence of an appropriately large lensing mass in our Chandra image and find weak diffuse emission near the quasar pair, with an X-ray flux typical of a group of galaxies at redshift z ~ 0.6. From our analysis of archival HST WFPC2 and NICMOS images, we find no evidence for a luminous lensing galaxy, but note a 3-sigma excess of galaxies in the UM425 field with plausible magnitudes for a z=0.6 galaxy group. However, the associated X-ray emission does not imply sufficient mass to produce the observed image splitting. The lens scenario thus requires a dark (high M/L ratio) lens, or a fortuitous configuration of masses along the line of sight. UM425 may instead be a close binary pair of BALQSOs, which would boost arguments that interactions and mergers increase nuclear activity and outflows.

13 pages, 9 figures, Accepted for publication in the Astrophysical Journal

References in corpus (10)

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• Continuum and Emission Line Strength Relations for a large Active Galactic Nuclei Sample
• The Evolution of a Mass-Selected Sample of Early-Type Field Galaxies
• Discovery of an ionized Fe-K edge in the z=3.91 Broad Absorption Line Quasar APM 08279+5255 with XMM-Newton
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• An FeLoBAL Binary Quasar
• Chandra discovery of the intracluster medium around UM425 at redshift 1.47

Cited by in corpus (10)

• An Exploratory Chandra Survey of a Well-Defined Sample of 35 Large Bright Quasar Survey Broad Absorption Line Quasars
• The Correlation between X-ray and UV Properties of BAL QSOs
• A Multiwavelength Study of Binary Quasars and Their Environments
• X-ray Absorption in Type II Quasars: Implications for the Equatorial Paradigm of Broad Absorption Line Quasars
• Strong Gravitational Lensing and the Structure of Quasar Outflows
• Discovery of the disturbed radio morphology in the interacting binary quasar FIRST J164311.3+315618
• Gravitational Microlensing and the Structure of Quasar Outflows
• The X-ray Spectrum and Spectral Energy Distribution of FIRST J155633.8+351758: a LoBAL Quasar with a Probable Polar Outflow
• Discovery of a Galaxy Cluster in the Foreground of the Wide-Separation Quasar Pair UM425
• The Discovery of Soft X-ray Loud Broad Absorption Line Quasars