Understanding extreme quasar optical variability with CRTS – II. Changing-state quasars

Graham, M. J.; Ross, Nicholas P.; Stern, Daniel; Drake, A. J.; McKernan, Barry; Ford, K. E. Saavik; Djorgovski, S. G.; Mahabal, A.; Glikman, Eilat; Larson, S. M.; Christensen, E.

doi:10.1093/mnras/stz3244

Cited by 90 publications

(70 citation statements)

References 79 publications

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“…A statistical search using optical light curves to initiate spectroscopic follow-up observations is proving an efficient CLQ finder, and, by design, our data sources and overall methodology, are in common to the recent Ross et al (2018), Stern et al (2018), and Graham et al (2020) papers.…”

Section: L Q S E L E C T I O N a N D L I N E M E A S U R E M E N T Smentioning

confidence: 99%

“…CRTS has been extensively used to study quasar variability (e.g. Graham et al 2014Graham et al , 2015aGraham et al , b, 2017Graham et al , 2020Stern et al 2017Stern et al , 2018Ross et al 2018).…”

Section: Optical Photometrymentioning

confidence: 99%

“…However, there are also examples of Mg II showing variations while H β does not, and vice versa. Graham et al (2020) report the largest number of H β CLQs to date, with a sample of 111 sources identified. Graham et al (2020) find that this population of extreme varying quasars, referred to as CSQs in their paper, is associated with changes in the Eddington ratio rather than simply the magnitude of the Eddington ratio itself.…”

Section: Continuum and Line Changes: Comparisons To Recent Observationsmentioning

confidence: 99%

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The first high-redshift changing-look quasars

Ross

Graham

Calderone

et al. 2020

Monthly Notices of the Royal Astronomical Society

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We report on three redshift z > 2 quasars with dramatic changes in their C iv emission lines, the first sample of changing-look quasars (CLQs) at high redshift. This is also the first time the changing-look behaviour has been seen in a high-ionisation emission line. SDSS J1205+3422, J1638+2827, and J2228+2201 show interesting behaviour in their observed optical light curves, and subsequent spectroscopy shows significant changes in the C iv broad emission line, with both line collapse and emergence being displayed on rest-frame timescales of ∼240-1640 days. These are rapid changes, especially when considering virial black hole mass estimates of MBH > 109M⊙ for all three quasars. Continuum and emission line measurements from the three quasars show changes in the continuum-equivalent width plane with the CLQs seen to be on the edge of the full population distribution, and showing indications of an intrinsic Baldwin effect. We put these observations in context with recent state-change models, and note that even in their observed low-state, the C iv CLQs are generally above ∼5% in Eddington luminosity.

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Section: L Q S E L E C T I O N a N D L I N E M E A S U R E M E N T Smentioning

confidence: 99%

Section: Optical Photometrymentioning

confidence: 99%

Section: Continuum and Line Changes: Comparisons To Recent Observationsmentioning

confidence: 99%

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The first high-redshift changing-look quasars

Ross

Graham

Calderone

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…An established population effect for quasars is the anticorrelation of continuum variability with the Eddington ratio (MacLeod et al 2012;Rumbaugh et al 2018;Graham et al 2020). Objects with larger Eddington ratios, linked to higher accretion rates, on average show a smaller amplitude in variability.…”

Section: Full Populationmentioning

confidence: 99%

“…MacLeod et al 2010). However a subset of Extremely Variable Quasars (EVQs) can, on the same timescales, show variability in the order of several (Lawrence et al 2016;Rumbaugh et al 2018;Graham et al 2020). Extreme continuum variability is closely linked to the concept of changing-look (CL) AGN (Tohline & Osterbrock 1976;Shappee et al 2014;LaMassa et al 2015;MacLeod et al 2016), in which the change in broad Hβ is such that the AGN changes between a type 1 E-mail: dhoman@roe.ac.uk and a type 2 classification (Khachikian & Weedman 1971;Osterbrock 1981).…”

Section: Introductionmentioning

confidence: 99%

Behaviour of the Mg ii 2798 Å line over the full range of AGN variability

Homan

MacLeod

Lawrence

et al. 2020

Monthly Notices of the Royal Astronomical Society

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We investigate the responsiveness of the 2798 Å Mg ii broad emission line in active galactic nuclei (AGNs) on time-scales of several years. Our study is based on a sample of extremely variable AGNs as well as a broad population sample. The observed response of the line in previous studies has been mixed. By focusing on extreme variability (|Δg| > 1), we find that Mg ii clearly does respond to the continuum. However, the degree of responsiveness varies strikingly from one object to another: We see cases of Mg ii changing by as much as the continuum, more than the continuum, or very little at all. In 74 per cent of the highly variable sample, the behaviour of Mg ii corresponds with that of H β, with 30 per cent of the objects showing large variations in both lines. We do not detect any change in the line width that would correspond to broad-line region ‘breathing’, in accordance with results from the literature. Some of the objects in our highly variable sample show a clear asymmetry in the Mg ii profile. This skewness can be both to the blue and the red of the line centre. Results from our broad population sample show that highly variable quasars have lower Eddington ratios. This result holds for the variability of the continuum, but the correlation is significantly reduced for the variability of the Mg ii line. For the first time, we present an overview of the value of the intrinsic Baldwin effect for Mg ii in a large sample.

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Modeling changing‐look active galactic nuclei phenomenon in 1D using accretion disk instabilities

2021

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Apart from regular, low-level stochastic variability, some active galactic nuclei (AGN) occasionally show exceptionally large changes in the luminosity, spectral shape, and/or X-ray absorption. The most notable are the changes of the spectral type when the source classified as a Seyfert 1 becomes a Seyfert 2 galaxy or vice versa. Thus, a name was coined of "changing-look AGN" (CL AGN). The origin of this phenomenon is still unknown, but for most of the sources, there are strong arguments in favor of the intrinsic changes. Understanding the nature of such rapid changes is a challenge to the models of black hole accretion flows since the timescales of the changes are much shorter than the standard disk viscous timescales. We aim to model the CL AGN phenomenon assuming that the underlying mechanism is the time-dependent evolution of a black hole accretion disk unstable due to the dominant radiation pressure. We use a one-dimensional, vertically integrated disk model, but we allow for the presence of the hot coronal layer above the disk and the presence of the inner purely hot flow. We focus on the variability timescales and amplitudes, which can be regulated by the action of large-scale magnetic fields, the description of the disk-corona coupling and the presence of an inner optically thin flow, like advection-dominated accretion flow. We compare model predictions for the accretion disk around black hole mass 10 7 M ⊙ .

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Understanding extreme quasar optical variability with CRTS – II. Changing-state quasars

Cited by 90 publications

References 79 publications

The first high-redshift changing-look quasars

The first high-redshift changing-look quasars

Behaviour of the Mg ii 2798 Å line over the full range of AGN variability

Modeling changing‐look active galactic nuclei phenomenon in 1D using accretion disk instabilities

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