Optical variability, absolute luminosity, and the Hubble diagram for QSOs

Pica, A. J.; Smith, Alex

doi:10.1086/161257

Cited by 58 publications

(55 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The qualitative result that the radio-loud quasars are more variable agrees with most of the past suggestions (Helfand et al 2001;Eggers et al 2000;Garcia et al 1999;Pica & Smith 1983). Since most blazars are radio-loud (e.g., Ulrich et al 1997), the higher variability amplitude of radio-loud quasars may reflect a higher fraction of blazars.…”

Section: Radio-detected Quasarssupporting

confidence: 87%

“…An anticorrelation between quasar variability and luminosity was reported by Angione & Smith (1972) and confirmed in numerous subsequent studies (Uomoto, Wills, & Wills 1976;Pica & Smith 1983;Lloyd 1984;O'Brien, Gondhalekar, & Wilson 1988;Hook et al 1994;Trèvese et al 1994; Cid Fernandes, Aretxaga, & Terlevich 1996;Cristiani et al 1996Cristiani et al , 1997Paltani & Courvoisier 1997;Giveon et al 1999;Garcia et al 1999;Hawkins 2000;Webb & Malkan 2000). Such an anticorrelation is expected in Poissonian models, although complex versions are necessary to explain the diversity of the relationship among quasars (Cid Fernandes, Sodré, & Vieira da Silva 2000).…”

Section: Introductionsupporting

confidence: 53%

“…Variability is sometimes found to be correlated with radio loudness (Pica & Smith 1983;Smith & Nair 1995;Garcia et al 1999;Eggers, Shaffer, & Weistrop 2000;Helfand et al 2001;Enya et al 2002), the equivalent width of the H line (Giveon et al 1999;Cid Fernandes et al 2000), and the presence of broad absorption line (BAL) troughs (Sirola et al 1998), although the results are not conclusive. No large X-ray-detected quasar sample has been systematically studied for optical variability, but since most blazars are X-ray-bright, a greater degree of variability may be expected from such a sample (e.g., Ulrich, Maraschi, & Urry 1997).…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

The Ensemble Photometric Variability of ∼25,000 Quasars in the Sloan Digital Sky Survey

Berk

Wilhite

Krön

et al. 2004

ApJ

411

452

View full text Add to dashboard Cite

Using a sample of over 25,000 spectroscopically confirmed quasars from the Sloan Digital Sky Survey, we show how quasar variability in the rest-frame optical/UV regime depends on rest-frame time lag, luminosity, rest wavelength, redshift, the presence of radio and X-ray emission, and the presence of broad absorption line systems. Imaging photometry is compared with three-band spectrophotometry obtained at later epochs spanning time lags up to about 2 yr. The large sample size and wide range of parameter values allow the dependence of variability to be isolated as a function of many independent parameters. The time dependence of variability (the structure function) is well fitted by a single power law with an index ¼ 0:246 AE 0:008, on timescales from days to years. There is an anticorrelation of variability amplitude with rest wavelength-e.g., quasars are about twice as variable at 1000 Å as at 6000 Å -and quasars are systematically bluer when brighter at all redshifts. There is a strong anticorrelation of variability with quasar luminosity-variability amplitude decreases by a factor of about 4 when luminosity increases by a factor of 100. There is also a significant positive correlation of variability amplitude with redshift, indicating evolution of the quasar population or the variability mechanism. We parameterize all of these relationships. Quasars with ROSAT All-Sky Survey X-ray detections are significantly more variable (at optical/UV wavelengths) than those without, and radio-loud quasars are marginally more variable than their radio-quiet counterparts. We find no significant difference in the variability of quasars with and without broad absorption line troughs. Currently, no models of quasar variability address more than a few of these relationships. Models involving multiple discrete events or gravitational microlensing are unlikely by themselves to account for the data. So-called accretion disk instability models are promising, but more quantitative predictions are needed.

show abstract

Section: Radio-detected Quasarssupporting

confidence: 87%

Section: Introductionsupporting

confidence: 53%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The Ensemble Photometric Variability of ∼25,000 Quasars in the Sloan Digital Sky Survey

Berk

Wilhite

Krön

et al. 2004

ApJ

411

452

View full text Add to dashboard Cite

show abstract

“…This was already considered in early studies of optical variability (e.g. Pica & Smith 1983;Aretxaga et al 1997), and, in its simplest version of independent and identical flares, would predict a variability amplitude ∝N −1/2 ∝ L −1/2 . In the X-ray domain, several authors have also considered the same argument (Green et al 1993;Nandra et al 1997;Almaini et al 2000;Manners et al 2002).…”

Section: Dependence On X-ray Luminosity and Redshiftmentioning

confidence: 80%

Ensemble X-ray variability of active galactic nuclei from serendipitous source catalogues

Vagnetti

Turriziani

Trèvese

2011

A&A

View full text Add to dashboard Cite

Context. The X-ray variability of the active galactic nuclei (AGN) has been most often investigated with studies of individual, nearby sources, and only a few ensemble analyses have been applied to large samples in wide ranges of luminosity and redshift. Aims. We aim to determine the ensemble variability properties of two serendipitously selected AGN samples extracted from the catalogues of XMM-Newton and Swift, with redshift between ∼0.2 and ∼4.5, and X-ray luminosities, in the 0.5-4.5 keV band, between ∼10 43 erg/s and ∼10 46 erg/s. Methods. We used the structure function (SF), which operates in the time domain, and allows for an ensemble analysis even when only a few observations are available for individual sources and the power spectral density (PSD) cannot be derived. The SF is also more appropriate than fractional variability and excess variance, because these parameters are biased by the duration of the monitoring time interval in the rest-frame, and therefore by cosmological time dilation. Results. We find statistically consistent results for the two samples, with the SF described by a power law of the time lag, approximately as SF ∝ τ 0.1 . We do not find evidence of the break in the SF, at variance with the case of lower luminosity AGNs. We confirm a strong anti-correlation of the variability with X-ray luminosity, accompanied by a change of the slope of the SF. We find evidence in support of a weak, intrinsic, average increase of X-ray variability with redshift. Conclusions. The change of amplitude and slope of the SF with X-ray luminosity provides new constraints on both single oscillator models and multiple subunit models of variability.

show abstract

“…Pica & Smith 1983;Hook et al 1994;Paltani & Courvoisier 1997;Vanden Berk et al 2004;De Vries et al 2005;Meusinger et al 2011). The main driver behind the V − L relation may be the Eddington ratio or the accretion rate (e.g.…”

Section: Variabilitymentioning

confidence: 99%

A large sample of Kohonen-selected SDSS quasars with weak emission lines: selection effects and statistical properties

Meusinger

Balafkan

2014

A&A

View full text Add to dashboard Cite

Aims. A tiny fraction of the quasar population shows remarkably weak emission lines. Several hypotheses have been developed, but the weak line quasar (WLQ) phenomenon still remains puzzling. The aim of this study was to create a sizeable sample of WLQs and WLQ-like objects and to evaluate various properties of this sample. Methods. We performed a search for WLQs in the spectroscopic data from the Sloan Digital Sky Survey Data Release 7 based on Kohonen self-organising maps for nearly 10 5 quasar spectra. The final sample consists of 365 quasars in the redshift range z = 0.6−4.2 (z = 1.50 ± 0.45) and includes in particular a subsample of 46 WLQs with equivalent widths W Mg  < 11 Å and W C  < 4.8 Å. We compared the luminosities, black hole masses, Eddington ratios, accretion rates, variability, spectral slopes, and radio properties of the WLQs with those of control samples of ordinary quasars. Particular attention was paid to selection effects. Results. The WLQs have, on average, significantly higher luminosities, Eddington ratios, and accretion rates. About half of the excess comes from a selection bias, but an intrinsic excess remains probably caused primarily by higher accretion rates. The spectral energy distribution shows a bluer continuum at rest-frame wavelengths > ∼ 1500 Å. The variability in the optical and UV is relatively low, even taking the variability-luminosity anti-correlation into account. The percentage of radio detected quasars and of core-dominant radio sources is significantly higher than for the control sample, whereas the mean radio-loudness is lower. Conclusions. The properties of our WLQ sample can be consistently understood assuming that it consists of a mix of quasars at the beginning of a stage of increased accretion activity and of beamed radio-quiet quasars. The higher luminosities and Eddington ratios in combination with a bluer spectral energy distribution can be explained by hotter continua, i.e. higher accretion rates. If quasar activity consists of subphases with different accretion rates, a change towards a higher rate is probably accompanied by an only slow development of the broad line region. The composite WLQ spectrum can be reasonably matched by the ordinary quasar composite where the continuum has been replaced by that of a hotter disk. A similar effect can be achieved by an additional power-law component in relativistically boosted radio-quiet quasars, which may explain the high percentage of radio quasars.

show abstract

Optical variability, absolute luminosity, and the Hubble diagram for QSOs

Cited by 58 publications

References 0 publications

The Ensemble Photometric Variability of ∼25,000 Quasars in the Sloan Digital Sky Survey

The Ensemble Photometric Variability of ∼25,000 Quasars in the Sloan Digital Sky Survey

Ensemble X-ray variability of active galactic nuclei from serendipitous source catalogues

A large sample of Kohonen-selected SDSS quasars with weak emission lines: selection effects and statistical properties

Contact Info

Product

Resources

About