A Synoptic Multiwavelength Analysis of a Large Quasar Sample

Rengstorf, A. W.; Brunner, Róbert; Wilhite, Brian C.

doi:10.1086/500585

Cited by 28 publications

(41 citation statements)

References 30 publications

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“…The error bar indicates the RMS within that bin, which is much larger than the value obtained from error propagation. For type I AGNs, the structure function with timescales larger than 10 days can generally be well fitted by power law function, with in-dex ∼ 0.3−0.4 (Vanden Berk et al 2004;Rengstorf et al 2006;Wilhite et al 2008;Meusinger et al 2011).…”

Section: Optical Variabilitymentioning

confidence: 97%

“…Another commonly used tool to test the variability is the structure function (Simonetti et al 1985;Kawaguchi et al 1998;Hawkins 2002;de Vries et al 2005;Bauer et al 2009;Meusinger et al 2011;di Clemente et al 1996;Vanden Berk et al 2004;Rengstorf et al 2006;Wilhite et al 2008), which shows the variability on timescales ranging from days to years. Here we used the modified structure function (SF) defined in di Clemente et al (1996) …”

Section: Optical Variabilitymentioning

confidence: 99%

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An Unobscured Type Ii Quasar Candidate: SDSS J012032.19-005501.9

Yuan

Zhou

et al. 2015

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We report the finding of an unobscured type II Active Galactic Nuclei (AGN) candidate, SDSS J012032.19-005501.9 at a relatively high redshift of 0.601, which shows a number of unusual properties. It varies significantly on timescales of years as typical type I AGNs and marginally on timescales of weeks. The color-magnitude relation and the structure function are also consistent with that of type I AGNs, which imply that its variability likely originates from the black hole accretion system. However, no broad emission line is detected in the SDSS spectrum, and the upper limit of the equivalent width of the Hβ broad emission line is much less than that of type I AGNs. These properties suggest that SDSS J012032.19-005501.9 may be an unobscured quasar without broad emission lines intrinsically, namely an unobscured type II AGN or "true" type II AGN. Furthermore, its continuum luminosity is at least one order of magnitude fainter than the average value of the past century expected from the [OIII] emission line. It indicates that SDSS J012032.19-005501.9 may be switching off. Additional possible scenarios to explain this intriguing source are also discussed. Future deep observations at multi-wavelengths are needed to reveal the nature of this peculiar and intriguing AGN.

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Section: Optical Variabilitymentioning

confidence: 97%

Section: Optical Variabilitymentioning

confidence: 99%

An Unobscured Type Ii Quasar Candidate: SDSS J012032.19-005501.9

Yuan

Zhou

et al. 2015

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“…Substantial improvement has been achieved with the advance of large surveys. Over approximately the last decade, large and well-defined quasar samples have provided a solid base for the statistical investigation of quasar variability (Vanden Berk et al 2004;de Vries et al 2005;Rengstorf et al 2006;Wold et al 2007;Wilhite et al 2005Wilhite et al , 2008Bauer et al 2009;Ai et al 2010;MacLeod et al 2010;Schmidt et al 2010Schmidt et al , 2012Zuo et al 2012). …”

Section: Introductionmentioning

confidence: 99%

Ultraviolet variability of quasars: dependence on the accretion rate

Meusinger

Weiss

2013

A&A

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Aims. Although the variability in the ultraviolet and optical domain is one of the major characteristics of quasars, the dominant underlying mechanisms are still poorly understood. There is a broad consensus on the relationship between the strength of the variability and such quantities as time-lag, wavelength, luminosity, and redshift. However, evidence on a dependence on the fundamental parameters of the accretion process is still inconclusive. This paper is focused on the correlation between the ultraviolet quasar long-term variability and the accretion rate. Methods. We compiled a catalogue of about 4000 quasars including individual estimators for the variability strength derived from the multi-epoch photometry in the SDSS Stripe 82, virial black hole masses M derived from the Mg  line, and mass accretion ratesṀ from the Davis-Laor scaling relation. Several statistical tests were applied to evaluate the correlations of the variability with luminosity, mass, Eddington ratio, and accretion rate. Results. We confirm the existence of significant anti-correlations between the variability estimator V and the accretion rateṀ, the Eddington ratio ε, and the bolometric luminosity L bol , respectively. The Eddington ratio is tightly correlated withṀ. A weak, statistically not significant positive trend is indicated for the dependence of V on M. As a side product, we find a strong correlation of the radiative efficiency η with M in our sample. We show via numerical simulations that this trend is most likely produced by selection effects in combination with the mass errors and the use of the scaling relation forṀ. The anti-correlations of V withṀ, ε, and L bol cannot be explained in such a way. The strongest anti-correlation is found between V andṀ. However, it is difficult to decide which of the quantities L, ε, andṀ is intrinsically correlated with V and which of the observed correlations of V are produced by the L − ε −Ṁ relation. A V −Ṁ anti-correlation is qualitatively expected for the strongly inhomogeneous accretion disks. We argue that the observed amplitudes of the variability at far-UV wavelengths, the stochastic nature of variability, and the variability time-scales are not adequately explained by the simple multi-temperature black-body model of a standard disk and suggest to check whether the strongly inhomogeneous disk model is capable of reproducing these observations better.

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“…Numerous studies have shown that the optical/UV continuum variability of quasars correlates with various physical parameters such as time-lag, rest-frame wavelength, luminosity, radio properties, emission line properties, and the Eddington ratio (e.g., Ulrich et al 1997;Giveon 1999;Helfand 2001;Gaskell & Klimek 2003;Vanden Berk et al 2004;Rengstorf et al 2006;Wold et al 2007;Wilhite et al 2008;Bauer et al 2009;Ai et al 2010;MacLeod et al 2010;Schmidt et al 2010). Despite considerable progress in the description of quasar variability, there are still conflicting claims about these correlations and their physical interpretation is fraught with problems.…”

Section: Introductionmentioning

confidence: 99%

Spectral variability of quasars from multi-epoch photometric data in the Sloan Digital Sky Survey Stripe 82

Meusinger

Hinze

Hoon

2010

A&A

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Aims. The study of the ensemble properties of the UV/optical broadband variability of quasars is hampered by the combined effects of the dependence of variability on timescale, rest-frame wavelength, and luminosity. Here, we present a new approach to analysing the dependence of quasar variability on rest-frame wavelengths. Methods. We exploited the spectral archive of the Sloan Digital Sky Survey (SDSS) to create a sample of over 9000 quasars in the Stripe 82. The quasar catalogue was matched with the Light Motion Curve Catalogue for SDSS Stripe 82 and first-order structure functions were computed from the lightcurves. The structure functions are used to create a variability indicator that is related to the same intrinsic timescales for all quasars (about 1 to 2 yr in the rest-frame). We study the variability ratios for adjacent SDSS filter bands as a function of redshift. A quantitative interpretation of these relations is provided by comparing with the results of simple Monte Carlo simulations of variable quasar spectra. Results. We confirm the well-known dependence of variability on time-lag; the best power-law fit of the sample-averaged structure function has a slope β = 0.31 ± 0.03. We also confirm that anti-correlations exist with luminosity, wavelength, and redshift, where the latter can be fully explained as a consequence of the former two dependencies. The variability ratios as a function of redshift resemble the corresponding colour index-redshift relations. While variability is almost always stronger in the bluer passband than in the redder, the variability ratio depends on whether strong emission lines contribute to either one band or the other. We find that the observed variability ratio-redshift relations are described well assuming that (a) the r.m.s. fluctuation of the quasar continuum flux follows a power law σ( f λ ) ∝ λ −2 (i.e., is bluer when brighter) and (b) the variability of the emission line flux is only ∼10% of that of the underlying continuum. These results, based upon the photometry of more than 8000 quasars, confirm the previous findings by Wilhite and collaborators for 315 quasars with repeated SDSS spectroscopy. Finally, we find that quasars with unusual spectra and weak emission lines tend to have less variability than conventional quasars. This trend is the opposite of that expected from the dilution effect of variability due to line emission and may be indicative of high Eddington ratios in these unusual quasars.

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A Synoptic Multiwavelength Analysis of a Large Quasar Sample

Cited by 28 publications

References 30 publications

An Unobscured Type Ii Quasar Candidate: SDSS J012032.19-005501.9

An Unobscured Type Ii Quasar Candidate: SDSS J012032.19-005501.9

Ultraviolet variability of quasars: dependence on the accretion rate

Spectral variability of quasars from multi-epoch photometric data in the Sloan Digital Sky Survey Stripe 82

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