Variability Tests for Intrinsic Absorption Lines in Quasar Spectra

Narayanan, Desika; Hamann, Fred; Barlow, Tom A.; Burbidge, E. M.; Cohen, R. D.; Junkkarinen, V. T.; Lyons, R.

doi:10.1086/380781

Cited by 88 publications

(141 citation statements)

References 33 publications

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“…While we cannot conclusively rule out the possibility of intervening systems contaminating our sample, we note that the velocity widths (greater than 1000 km s −1 ) required for mini-BALs would require a high spread of velocities in any intervening absorber sufficient to broaden the absorption feature (which has doublet lines spaced ≈500 km s −1 apart) by ≈500 km s −1 . In general, mini-BALs have also been observed to vary more commonly than do NALs (e.g., Narayanan et al 2004, and references therein), and several of our results are consistent with those of Misawa et al (2008), which were obtained for a small sample of narrow absorption lines which were known to be variable. Variability is commonly taken to indicate that the absorber is relatively compact and therefore likely to be intrinsic.…”

Section: Are Mini-bals Just Narrow Bals?supporting

confidence: 89%

X-Ray Insights Into the Physics of Mini-Bal Quasar Outflows

Gibson

Brandt

Gallagher

et al. 2009

ApJ

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We examine the ultraviolet and X-ray properties of 256 radio-quiet Sloan Digital Sky Survey quasars (QSOs) observed in X-rays with Chandra and/or XMM-Newton in order to study the relationship between QSOs with broad C iv absorption lines (BALs; width > 2000 km s −1 ) and those with C iv mini-BALs (here defined to have widths of 1000-2000 km s −1 ). Our sample includes 42 BAL and 48 mini-BAL QSOs. The relative X-ray brightness and hard spectral slopes of the mini-BAL population are, on average, intermediate between those of BAL and non-BAL QSOs, as might be expected if narrower and broader absorption line outflows are physically related. However, a significant population of mini-BALs has outflow velocities higher than would be expected for BAL QSOs of the same relative X-ray brightness. Consistently strong X-ray absorption is apparently not required to accelerate at least some mini-BALs to high outflow velocities. Assuming the mini-BAL features are correctly attributed to intrinsic C iv absorption, we suggest that their observed properties may be explained if mini-BALs are "seeds" that can be accelerated to form BALs when sufficient X-ray shielding is present. We also examine several QSOs with broad C iv absorption that have been recently reported to be unusually X-ray bright. Such cases are frequently mini-BAL QSOs, which, as a population, are generally brighter in X-rays than BAL QSOs. Pointed XMM-Newton observations also suggest that these sources (or unresolved neighbors) may have been previously observed in a high-flux state.

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Section: Are Mini-bals Just Narrow Bals?supporting

confidence: 89%

X-Ray Insights Into the Physics of Mini-Bal Quasar Outflows

Gibson

Brandt

Gallagher

et al. 2009

ApJ

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“…Therefore, it is difficult to distinguish intrinsic NALs from intervening and associated absorption lines in the same spectrum, especially in low or moderate resolution spectra. Many previous studies have revealed that intrinsic absorption lines can vary in equivalent width over timescales of months to years (e.g., Wise et al 2004;Narayanan et al 2004;Gibson et al 2008Gibson et al , 2010Hamann et al 2011;Hacker et al 2013;Chen & Qin 2013;Misawa et al 2014). The line variability is a good indicator to determine whether NALs are truly intrinsic to quasars or not.…”

Section: Introductionmentioning

confidence: 99%

Narrow absorption lines with two observations from the Sloan Digital Sky Survey

Chen¹,

Gu²,

Chen³

et al. 2015

Monthly Notices of the Royal Astronomical Society

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We assemble 3524 quasars from Sloan Digital Sky Survey (SDSS) with repeated observations to search for variations of narrow C IVλλ1548, 1551 and Mg IIλλ2796, 2803 absorption doublets in spectral regions shortward of 7000Å at the observed frame, which corresponds to time-scales of about 150 ∼ 2643 days at quasar rest frame. In these quasar spectra, we detect 3580 C IV absorption systems with z abs = 1.5188 ∼ 3.5212, and 1809 Mg II absorption systems with z abs = 0.3948 ∼ 1.7167. In term of the absorber velocity (β) distribution at quasar rest frame, we find a substantial number of C IV absorbers with β < 0.06, which might be connected to the absorptions of quasar outflows. The outflow absorptions peak at υ ≈ 2000 km s −1 and drop rapidly below the peak value. Among 3580 C IV absorption systems, 52 systems (∼ 1.5%) show obvious variations in equivalent widths at the absorber rest frame (W r ): 16 enhanced, 16 emerged, 12 weaken, and 8 disappeared systems, respectively. We find that changes in W r λ1548 are neither related to time-scales of the two SDSS observations, nor to absorber velocities at the quasar rest frame. Variable absorptions in low-ionization species are important to constraint the physical conditions of absorbing gas. There are two variable Mg II absorption systems measured from SDSS spectra detected by Hacker et al. However, in our Mg II absorption sample, we find that neither shows variable absorption with confident levels of > 4σ for λ2796 lines and > 3σ for λ2803 lines.

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“…These results suggest that the absorber covers the background source entirely in the direction of this line of sight. Nevertheless, we still cannot rule out an intrinsic origin for systems C and D in the vicinity of the quasar (within 1000 km s À1 ), especially because a number of intrinsic NALs have been detected at small velocities from quasars (e.g., Ganguly et al 1999;Narayanan et al 2004;Wise et al 2004). We discuss these systems in x 6.…”

Section: Results: Notes On Eight C Iv Systemsmentioning

confidence: 94%

“…Therefore, we adopt the simplifying assumptions of Hamann et al (1997b) and Narayanan et al (2004), namely, (1) the gas is very close to ionization equilibrium, (2) changes in the ionizing flux are small, and (3) C iv is the dominant ionization state of C. Under these assumptions we can use the recombination timescale as a means of estimating the electron density (eq. [1] in Hamann et al 1997b;eq. [1] in Narayanan et al 2004; the recombination coefficient corresponds to a nominal gas temperature of 20,000 K, after Hamann et al 1995). Using the rest-frame variability timescale (t var ¼ 0:36 yr) as an upper limit to the recombination time, we estimate the minimum electron density to be n e k 3 ; 10 4 cm À3 .…”

Section: Change Of the Ionization Statementioning

confidence: 99%

“…We can use several criteria to separate intrinsic NALs from intervening NALs, e.g., time variability, high electron density, partial coverage, polarization, line profile, high ionization state, and high metallicity ( Barlow & Sargent 1997;Hamann et al 1997b and references therein). Among them, two methods, (1) time variability analysis and (2) covering factor analysis, are the most reliable and most frequently applied (e.g., Barlow et al 1992;Hamann et al 1997aHamann et al , 1997bBarlow & Sargent 1997;Goodrich & Miller 1995;Ganguly et al 1999Ganguly et al , 2003Misawa et al 2003;Narayanan et al 2004;Wise et al 2004).…”

Section: Introductionmentioning

confidence: 99%

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Time-Variable Complex Metal Absorption Lines in the Quasar HS1603+3820

Misawa

Eracleous²,

Charlton³

et al. 2006

AIP Conference Proceedings

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We present a new spectrum of the quasar HS 1603+3820 taken 1.28 yr (0.36 yr in the quasar rest frame) after a previous observation with Subaru+HDS. The new spectrum enables us to search for time variability as an identifier of intrinsic narrow absorption lines ( NALs). This quasar shows a rich complex of C iv NALs within 60,000 km s À1 of the emission redshift. On the basis of covering factor analysis, Misawa et al. found that the C iv NAL system at z abs ¼ 2:42 2:45 (system A, at a shift velocity of v sh ¼ 8300 10;600 km s À1 relative to the quasar) was intrinsic to the quasar. With our new spectrum, we perform time variability analysis, as well as covering factor analysis, to separate intrinsic NALs from intervening NALs for eight C iv systems. Only system A, which was identified as an intrinsic system in the earlier paper by Misawa et al., shows a strong variation in line strength (W obs % 10:4 !19:1 8). We speculate that a broad absorption line (BAL) could be forming in this quasar (i.e., many narrower lines will blend together to make a BAL profile). We illustrate the plausibility of this suggestion with the help of a simulation in which we vary the column densities and covering factors of the NAL complex. Under the assumption that a change of ionization state causes the variability, a lower limit can be placed on the electron density (n e k 3 ; 10 4 cm À3 ) and an upper limit on the distance from the continuum source (r 6 kpc). On the other hand, if the motion of clumpy gas causes the variability (a more likely scenario), the crossing velocity and the distance from the continuum source are estimated to be v cross > 8000 km s À1 and r < 3 pc. In this case, the absorber does not intercept any flux from the broad emission line region, but only flux from the UV continuum source. If we adopt the dynamical model of Murray et al., we can obtain a much more strict constraint on the distance of the gas parcel from the continuum source, r < 0:2 pc.

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Variability Tests for Intrinsic Absorption Lines in Quasar Spectra

Cited by 88 publications

References 33 publications

X-Ray Insights Into the Physics of Mini-Bal Quasar Outflows

X-Ray Insights Into the Physics of Mini-Bal Quasar Outflows

Narrow absorption lines with two observations from the Sloan Digital Sky Survey

Time-Variable Complex Metal Absorption Lines in the Quasar HS1603+3820

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