The Color Variability of Quasars

Schmidt, Kasper B.; Rix, H. W.; Shields, J. C.; Knecht, Matthias; Hogg, David W.; Maoz, Dan; Bovy, Jo

doi:10.1088/0004-637x/744/2/147

Cited by 104 publications

(142 citation statements)

References 72 publications

Supporting

Mentioning

124

Contrasting

Order By: Relevance

“…Only Trevese et al (1994) binned the magnitude limited sample within small luminosity and redshift ranges and found an anti-correlation, which is ascribed to the dependence of variability on wavelength. Some previous work (Giveon et al 1999;Schmidt et al 2012) also found no relation between V and z. After correcting the contribution from emission lines, the color variability is independent of redshift (Schmidt et al 2012), which agrees with our results.…”

Section: Comparison With Previous Worksupporting

confidence: 93%

“…Some previous work (Giveon et al 1999;Schmidt et al 2012) also found no relation between V and z. After correcting the contribution from emission lines, the color variability is independent of redshift (Schmidt et al 2012), which agrees with our results. However, although Giveon et al (1999) also found no relation between V and z, their conclusion is probably not reliable due to the small size and the narrow redshift range of the quasar sample.…”

Section: Comparison With Previous Worksupporting

confidence: 93%

“…However, as quasar optical luminosities are dominated by their disks rather than their host galaxies, accretion disk instabilities are more likely than influences of host galaxies to explain the bluer-whenbrighter chromatism. Trevese & Vagnetti (2001, 2002 analyzed the dependence of spectral changes on the brightness of quasars and suggested that the chromatism is at least consistent with the temperature variation of a single emitting blackbody and can be explained by bright spots on the disk possibly produced by the accretion disk instability, which also agrees with Schmidt et al (2012). It is also possible that a combination of these physical mechanisms produces the color chromatism.…”

Section: Comparison With Previous Workmentioning

confidence: 75%

See 2 more Smart Citations

The correlations between optical variability and physical parameters of quasars in SDSS Stripe 82

Zuo¹,

Wu²,

Liu³

et al. 2012

Proc. IAU

View full text Add to dashboard Cite

We investigate the optical variability of 7658 quasars from SDSS Stripe 82. Taking advantage of a larger sample and relatively more data points for each quasar, we estimate variability amplitudes and divide the sample into small bins of redshift, rest-frame wavelength, black hole mass, Eddington ratio and bolometric luminosity respectively, to investigate the relationships between variability and these parameters. An anti-correlation between variability and rest-frame wavelength is found. The variability amplitude of radio-quiet quasars shows almost no cosmological evolution, but that of radio-loud ones may weakly anticorrelate with redshift. In addition, variability increases as either luminosity or Eddington ratio decreases. However, the relationship between variability and black hole mass is uncertain; it is negative when the influence of Eddington ratio is excluded, but positive when the influence of luminosity is excluded. The intrinsic distribution of variability amplitudes for radio-loud and radio-quiet quasars are different. Both radio-loud and radio-quiet quasars exhibit a bluer-whenbrighter chromatism. Assuming that quasar variability is caused by variations of accretion rate, the Shakura-Sunyaev disk model can reproduce the tendencies of observed correlations between variability and rest-frame wavelength, luminosity as well as Eddington ratio, supporting that changes of accretion rate plays an important role in producing the observed optical variability. However, the predicted positive correlation between variability and black hole mass seems to be inconsistent with the observed negative correlation between them in small bins of Eddington ratio, which suggests that other physical mechanisms may still need to be considered in modifying the simple accretion disk model.

show abstract

Section: Comparison With Previous Worksupporting

confidence: 93%

Section: Comparison With Previous Worksupporting

confidence: 93%

Section: Comparison With Previous Workmentioning

confidence: 75%

See 1 more Smart Citation

The correlations between optical variability and physical parameters of quasars in SDSS Stripe 82

Zuo¹,

Wu²,

Liu³

et al. 2012

Proc. IAU

View full text Add to dashboard Cite

show abstract

“…While an inhomogeneous disk has been demonstrated to fit composite difference spectra (Ruan et al 2014) and color variability of quasars (Schmidt et al 2012), Hung et al (2016) find a simple disk model adequate to fit differenceflux UV/optical spectral energy distributions of individual quasars. Moreover, Kokubo (2015) argues that the tight interband correlations observed in SDSS quasar light curves are inconsistent with the inhomogeneous disk model.…”

Section: Accretion Disk Instabilitiesmentioning

confidence: 99%

iPTF Discovery of the Rapid “Turn-on” of a Luminous Quasar

Gezari

Hung

Cenko

et al. 2017

ApJ

137

175

View full text Add to dashboard Cite

We present a radio-quiet quasar at z=0.237 discovered "turning on" by the intermediate Palomar Transient Factory (iPTF). The transient, iPTF 16bco, was detected by iPTF in the nucleus of a galaxy with an archival Sloan Digital Sky Survey spectrum with weak narrow-line emission characteristic of a low-ionization nuclear emissionline region (LINER). Our follow-up spectra show the dramatic appearance of broad Balmer lines and a power-law continuum characteristic of a luminous ( » L 10 bol 45 erg s −1 ) type 1 quasar 12 yr later. Our photometric monitoring with PTF from 2009-2012 and serendipitous X-ray observations from the XMM-Newton Slew Survey in 2011 and 2015 constrain the change of state to have occurred less than 500 days before the iPTF detection. An enhanced broad Hα/[O III] λ5007 line ratio in the type 1 state relative to other changing-look quasars also is suggestive of the most rapid change of state yet observed in a quasar. We argue that the >10 increase in Eddington ratio inferred from the brightening in UV and X-ray continuum flux is more likely due to an intrinsic change in the accretion rate of a preexisting accretion disk than an external mechanism such as variable obscuration, microlensing, or the tidal disruption of a star. However, further monitoring will be helpful in better constraining the mechanism driving this change of state. The rapid "turn-on" of the quasar is much shorter than the viscous infall timescale of an accretion disk and requires a disk instability that can develop around a  M 10 8 black hole on timescales less than 1 yr.

show abstract

“…Because of the high luminosity of the objects presented here, several differences in the properties are expected as compared to those of the global quasar population. The physical scales locally are expected to be larger (Bentz et al 2013), which will make variability timescales longer and variability magnitudes smaller (Vanden Berk et al 2004;Schmidt et al 2012). Blackhole masses as determined from Mg  increases with luminosity (Wu et al 2015) which in turn affects the temperature of the accretion disc (Shakura & Sunyaev 1973;Pereyra et al 2006) and thereby the position of the "big blue bump" and the degree to which the continuum is well modeled by a single power law (see also Lusso et al 2015, for a discussion).…”

Section: Comparison To Global Populationmentioning

confidence: 99%

An X-Shooter composite of bright 1 <z< 2 quasars from UV to infrared

Selsing

Fynbo

Christensen

et al. 2015

A&A

160

180

View full text Add to dashboard Cite

Quasi-stellar object (QSO) spectral templates are important both to QSO physics and for investigations that use QSOs as probes of intervening gas and dust. However, combinations of various QSO samples obtained at different times and with different instruments so as to expand a composite and to cover a wider rest frame wavelength region may create systematic effects, and the contribution from QSO hosts may contaminate the composite. We have constructed a composite spectrum from luminous blue QSOs at 1 < z < 2.1 selected from the Sloan Digital Sky Survey (SDSS). The observations with X-Shooter simultaneously cover ultraviolet (UV) to nearinfrared (NIR) light, which ensures that the composite spectrum covers the full rest-frame range from Lyβ to 11 350 Å without any significant host contamination. Assuming a power-law continuum for the composite we find a spectral slope of α λ = 1.70 ± 0.01, which is steeper than previously found in the literature. We attribute the differences to our broader spectral wavelength coverage, which allows us to effectively avoid fitting any regions that are affected either by strong QSO emissions lines (e.g., Balmer lines and complex [Fe II] blends) or by intrinsic host galaxy emission. Finally, we demonstrate the application of the QSO composite spectrum for evaluating the reddening in other QSOs.

show abstract

The Color Variability of Quasars

Cited by 104 publications

References 72 publications

The correlations between optical variability and physical parameters of quasars in SDSS Stripe 82

The correlations between optical variability and physical parameters of quasars in SDSS Stripe 82

iPTF Discovery of the Rapid “Turn-on” of a Luminous Quasar

An X-Shooter composite of bright 1 <z< 2 quasars from UV to infrared

Contact Info

Product

Resources

About