Quasar broad absorption line variability measurements using reconstructions of un-absorbed spectra

Abstract

We present a two-epoch Sloan Digital Sky Survey and Gemini/GMOS+William Herschel Telescope/ISIS variability study of 50 broad absorption line quasars of redshift range 1.9 < z < 4.2, containing 38 Si IV and 59 C IV BALs and spanning rest-frame time intervals of approximately 10 months to 3.7 years. We find that 35/50 quasars exhibit one or more variable BALs, with 58% of Si IV and 46% of C IV BALs showing variability across the entire sample. On average, Si IV BALs show larger fractional change in BAL pseudo equivalent width than C IV BALs, as referenced to an unabsorbed continuum+emission-line spectrum constructed using non-negative matrix factorisation. No correlation is found between BAL variability and quasar luminosity, suggesting that ionizing continuum changes do not play a significant role in BAL variability (assuming the gas is in photoionization equilibrium with the ionizing continuum). A subset of 14 quasars have one variable BAL from each of Si IV and C IV with significant overlap in velocity space and for which variations are in the same sense (strengthening or weakening) and which appear to be correlated (98% confidence). We find examples of both appearing and disappearing BALs in weaker/shallower lines with disappearance rates of 2.3% for C IV and 5.3% for Si IV, suggesting average lifetimes of 142 and 43 years respectively. We identify 5 objects in which the BAL is coincident with the broad emission-line, but appears to cover only the continuum source. Assuming a clumpy inhomogeneous absorber model and a typical size for the continuum source, we infer a maximum cloud radius of 10^13 to 10^14 cm, assuming Eddington limited accretion.

Accepted for publication in MNRAS. 22 pages, 12 figures, 7 tables

References in corpus (10)

• A Catalog of Quasar Properties from SDSS DR7
• The Radius-Luminosity Relationship for Active Galactic Nuclei: The Effect of Host-Galaxy Starlight on Luminosity Measurements
• The Intrinsic Fraction of Broad Absorption Line Quasars
• Quasar Broad Absorption Line Variability on Multi-Year Time Scales
• Broad Absorption Line Disappearance on Multi-Year Timescales in a Large Quasar Sample
• Broad Absorption Line Variability in Repeat Quasar Observations from the Sloan Digital Sky Survey
• Tombaugh 2: The First Open Cluster with a Significant Abundance Spread or Embedded in a Cold Stellar Stream?
• Variability in Quasar Broad Absorption Line Outflows III. What Happens on the Shortest Time-scales?
• Observational Constraints on the Dependence of Radio-Quiet Quasar X-ray Emission on Black Hole Mass and Accretion Rate
• On the diversity and complexity of absorption line profiles produced by outflows in Active Galactic Nuclei

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• A Variable PV Broad Absorption Line and Quasar Outflow Energetics
• Correlation between the variation of the ionizing continuum and broad absorption lines
• Photoionization-driven Absorption Lines Variability in Balmer Absorption Line Quasar LBQS 1206+1052
• C IV BAL disappearance in a large SDSS QSO sample
• Ionization driven intrinsic absorption line variability of BAL quasars in the Stripe 82 region
• Evidence for photoionization-driven variability in narrow absorption lines
• Saturation Effect on Photoionization-driven Broad Absorption Line Variability
• Extreme Variability in a Broad Absorption Line Quasar
• Correlation between the ionizing continuum and variable C iv broad absorption line in multi-epoch observations of SDSS J141007.74+541203.3
• Correlations between the Variation of the Ionizing Continuum and Broad Absorption Lines in Individual Quasars
• SDSS J1138+3517: A quasar showing remarkably variable broad absorption lines
• SALT long-slit spectroscopy of HE 0435-4312: fast displacement in the Mg II emission line