Evidence for Photoionization-Driven Broad Absorption Line Variability

Wang, Tinggui; Yang, Chenwei; Wang, Huiyuan; Ferland, Gary J.

doi:10.1088/0004-637x/814/2/150

Cited by 69 publications

(133 citation statements)

References 78 publications

(146 reference statements)

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“…Coordinated BAL variability over a large velocity interval (e.g., greater than ∼10 000 km s −1 ) is more easily explained by situations involving an ionization change; such behavior in the transverse-motion scenario would require coordinated motions of gas that would presumably exist at a large range of distances from the SMBH (see e.g., Hamann et al 2011;Capellupo et al 2013;Grier et al 2015;Wang et al 2015). Fig.…”

Section: Evidence For Ionization Changesmentioning

confidence: 99%

Broad absorption line disappearance and emergence using multiple-epoch spectroscopy from the Sloan Digital Sky Survey

McGraw

Brandt

Grier

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We investigate broad absorption line (BAL) disappearance and emergence using a 470 BAL-quasar sample over ≤ 0.10-5.25 rest-frame years with at least three spectroscopic epochs for each quasar from the Sloan Digital Sky Survey. We identify 14 disappearing BALs over ≤ 1.73-4.62 rest-frame years and 18 emerging BALs over ≤ 1.46-3.66 rest-frame years associated with the C iv λλ1548,1550 and/or Si iv λλ1393,1402 doublets, and report on their variability behavior. BAL quasars in our dataset exhibit disappearing/emerging C iv BALs at a rate of 2.3 +0.9 −0.7 and 3.0 +1.0 −0.8 per cent, respectively, and the frequency for BAL to non-BAL quasar transitions is 1.7 +0.8 −0.6 per cent. We detect four re-emerging BALs over ≤ 3.88 rest-frame years on average and three re-disappearing BALs over ≤ 4.15 rest-frame years on average, the first reported cases of these types. We infer BAL lifetimes along the line of sight to be nominally < ∼ 100-1000 yr using disappearing C iv BALs in our sample. Interpretations of (re-)emerging and (re-)disappearing BALs reveal evidence that collectively supports both transverse-motion and ionization-change scenarios to explain BAL variations. We constrain a nominal C iv/Si iv BAL outflow location of < ∼ 100 pc from the central source and a radial size of > ∼ 1×10 −7 pc (0.02 au) using the ionization-change scenario, and constrain a nominal outflow location of < ∼ 0.5 pc and a transverse size of ∼0.01 pc using the transverse-motion scenario. Our findings are consistent with previous work, and provide evidence in support of BALs tracing compact flow geometries with small filling factors.

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Section: Evidence For Ionization Changesmentioning

confidence: 99%

Broad absorption line disappearance and emergence using multiple-epoch spectroscopy from the Sloan Digital Sky Survey

McGraw

Brandt

Grier

et al. 2017

Monthly Notices of the Royal Astronomical Society

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“…While variability in BAL trough strengths is relatively common, large (>50%) changes in the absorption equivalent width is quite rare (e.g., Hall et al 2011). A primary question in BAL variability studies has been whether observed changes in BAL trough strengths are primarily due to changes in the ionization state of the outflowing wind (e.g., Wang et al 2015), or whether they are due to high column density BAL clouds moving through our line of sight (e.g., McGraw et al 2015).…”

Section: Introductionmentioning

confidence: 99%

Extreme Variability in a Broad Absorption Line Quasar

Stern

Graham

Arav

et al. 2017

ApJ

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CRTSJ084133.15+200525.8 is an optically bright quasar at z=2.345 that has shown extreme spectral variability over the past decade. Photometrically, the source had a visual magnitude of V∼17.3 between 2002 and 2008. Then, over the following five years, the source slowly brightened by approximately one magnitude, to V∼16.2. Only ∼1 in 10,000 quasars show such extreme variability, as quantified by the extreme parameters derived for this quasar assuming a damped random walk model. A combination of archival and newly acquired spectra reveal the source to be an iron low-ionization broad absorption line quasar with extreme changes in its absorption spectrum. Some absorption features completely disappear over the 9 years of optical spectra, while other features remain essentially unchanged. We report the first definitive redshift for this source, based on the detection of broad Hα in a Keck/MOSFIRE spectrum. Absorption systems separated by several 1000 km s −1 in velocity show coordinated weakening in the depths of their troughs as the continuum flux increases. We interpret the broad absorption line variability to be due to changes in photoionization, rather than due to motion of material along our line of sight. This source highlights one sort of rare transition object that astronomy will now be finding through dedicated timedomain surveys.

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“…For instance, cases where variations in the observed flux and in the absorption lines are correlated, are consistent with changes in the ionization state of gas (e.g. Wang et al 2015. Cases where the trough varies simultaneously at a wide range of outflow velocities can also be explained by this scenario (Hamman et al 2011, even if there is no information on the flux variability of the central source.…”

Section: Introductionmentioning

confidence: 89%

Hubble Space Telescope observations of BALQSO Ton 34 reveal a connection between the broad-line region and the BAL outflow

Krongold¹,

Binette²,

Bohlin³

et al. 2017

Monthly Notices of the Royal Astronomical Society

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Ton 34 recently transitioned from non-absorbing quasar into a BALQSO.Here, we report new HST-STIS observations of this quasar. Along with CIV absorption, we also detect absorption by NV+Lyα and possibly O VI+Lyβ. We follow the evolution of the CIV BAL, and find that, for the slower outflowing material, the absorption trough varies little (if at all) on a rest-frame timescale of ∼ 2 yr. However, we detect a strong deepening of the absorption in the gas moving at larger velocities (−20, 000 -−23, 000 km s −1 ). The data is consistent with a multistreaming flow crossing our line of sight to the source. The transverse velocity of the flow should be ∼ few thousand km s −1 , similar to the rotation velocity of the BLR gas (≈ 2, 600 km s −1 ). By simply assuming Keplerian motion, these two components must have similar locations, pointing to a common outflow forming the BLR and the BAL. We speculate that BALs, mini-BALs, and NALs, are part of a common, ubiquitous, accretion-disk outflow in AGN, but become observable depending on the viewing angle towards the flow. The absorption troughs suggests a wind covering only ∼20 % of the emitting source, implying a maximum size of 10 −3 pc for the clouds forming the BAL/BLR medium. This is consistent with constraints of the BLR clouds from X-ray occultations. Finally, we suggest that the low excitation broad emission lines detected in the spectra of this source lie beyond the wind, and this gas is probably excited by the shock of the BAL wind with the surrounding medium.

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Evidence for Photoionization-Driven Broad Absorption Line Variability

Cited by 69 publications

References 78 publications

Broad absorption line disappearance and emergence using multiple-epoch spectroscopy from the Sloan Digital Sky Survey

Broad absorption line disappearance and emergence using multiple-epoch spectroscopy from the Sloan Digital Sky Survey

Extreme Variability in a Broad Absorption Line Quasar

Hubble Space Telescope observations of BALQSO Ton 34 reveal a connection between the broad-line region and the BAL outflow

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