The Effects of Large-scale Magnetic Fields on the Model for Repeating Changing-look AGNs

Pan, Xin; Li, Shuang-Liang; Cao, Xinwu

doi:10.3847/1538-4357/abe766

Cited by 19 publications

(20 citation statements)

References 62 publications

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“…Assuming a BH mass of 10 7 M ⊙ with Eddington-limited accretion rate m Edd = 1 and inner radius R 0 = 3R g , we estimate the value of τ fill to be ≳ 56 months even for a small truncation radius of 4 R g with α = 0.1, which is much longer than the observed duration (≲ 3 months) of the faint state for J0456−20. This timescale can be significantly shortened as in a toy model developed by Sniegowska et al (2020) (see also Pan et al 2021), in which the radiation pressure instability only operates in a narrow ring between a thin outer disk and an optically thin hot inner ADAF. However, our X-ray spectral analysis suggests that the temperature of the inner-region of the multi-colour disk does not change at different X-ray flux states.…”

Section: Other Potential Scenariosmentioning

confidence: 99%

Deciphering the extreme X-ray variability of the nuclear transient eRASSt J045650.3−203750

Liu

Malyali

Krumpe

et al. 2023

A&A

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Context. During its all-sky survey, the extended ROentgen Survey with an Imaging Telescope Array (eROSITA) on board the Spectrum-Roentgen-Gamma (SRG) observatory has uncovered a growing number of X-ray transients associated with the nuclei of quiescent galaxies. Benefitting from its large field of view and excellent sensitivity, the eROSITA window into time-domain X-ray astrophysics yields a valuable sample of X-ray selected nuclear transients. Multi-wavelength follow-up enables us to gain new insights into understanding the nature and emission mechanism of these phenomena. Aims. We present the results of a detailed multi-wavelength analysis of an exceptional repeating X-ray nuclear transient, eRASSt J045650.3−203750 (hereafter J0456−20), uncovered by SRG/eROSITA in a quiescent galaxy at a redshift of z ∼ 0.077. We aim to understand the radiation mechanism at different luminosity states of J0456−20, and provide further evidence that similar accretion processes are at work for black hole accretion systems at different black hole mass scales. Methods. We describe our temporal analysis, which addressed both the long-and short-term variability of J0456−20. A detailed X-ray spectral analysis was performed to investigate the X-ray emission mechanism. Results. Our main findings are that 1) J0456−20 cycles through four distinctive phases defined based on its X-ray variability: anX-ray rising phase leading to an X-ray plateau phase that lasts for about two months. This is terminated by a rapid X-ray flux drop phase during which the X-ray flux can drop drastically by more than a factor of 100 within one week, followed by an X-ray faint state for about two months before the X-ray rising phase starts again. 2) The X-ray spectra are generally soft in the rising phase, with a photon index ≳ 3.0, and they become harder as the X-ray flux increases. There is evidence of a multi-colour disk with a temperature of T in ∼ 70 eV in the inner region at the beginning of the X-ray rising phase. The high-quality XMM-Newton data suggest that a warm and hot corona might cause the X-ray emission through inverse Comptonisation of soft disk seed photons during the plateau phase and at the bright end of the rising phase. 3) J0456−20 shows only moderate UV variability and no significant optical variability above the host galaxy level. Optical spectra taken at different X-ray phases are constant in time and consistent with a typical quiescent galaxy with no indication of emission lines. 4) Radio emission is (as yet) only detected in the X-ray plateau phase and rapidly declines on a timescale of two weeks. Conclusions. J0456−20 is likely a repeating nuclear transient with a tentative recurrence time of ∼223 days. It is a new member of this rare class. We discuss several possibilities to explain the observational properties of J0456−20. We currently favour a repeating partial tidal disruption event as the most likely scenario. The long-term X-ray evolution is explained as a transition between a thermal disk-dominated soft state and a steep power-la...

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Section: Other Potential Scenariosmentioning

confidence: 99%

Deciphering the extreme X-ray variability of the nuclear transient eRASSt J045650.3−203750

Liu

Malyali

Krumpe

et al. 2023

A&A

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“…Śniegowska et al (2020) proposed a simple time-dependent toy model of an accretion disk under radiation pressure instability, in which the timescale of the outbursts was regulated by the thickness of the unstable zone. Pan et al (2021) presented an extension of the Śniegowska et al (2020) model by adding a magnetic field and showed that the timescale of the outbursts can be significantly reduced by the magnetic fields. The possibility of shortening the timescales in CL AGN phenomena by magnetization of the accretion disk was also suggested by Dexter & Begelman (2019).…”

Section: Introductionmentioning

confidence: 99%

Modified models of radiation pressure instability applied to 10, 10⁵, and 10⁷ M_⊙ accreting black holes

Śniegowska

Grzȩdzielski

Czerny

et al. 2023

A&A

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Context. Some accreting black holes exhibit much stronger variability patterns than the usual stochastic variations. Radiation pressure instability is one of the proposed mechanisms that might account for this effect. Aims. We model luminosity changes for objects with a black hole mass of 10, 105, and 107 solar masses, using the time-dependent evolution of an accretion disk that is unstable as a result of the dominant radiation pressure. We concentrate on the outburst timescales. We explore the influence of the hot coronal flow above the cold disk, the inner purely hot flow, and the effect of the magnetic field on the time evolution of the disk-corona system. For intermediate-mass black holes and active galactic nuclei, we also explore the role of the disk outer radius because a disk that is fed by tidal disruption events (TDE) can be quite small. Methods. We used a 1D vertically integrated time-dependent numerical scheme that models the simultaneous evolution of the disk and corona, which is coupled by the vertical mass exchange. We parameterized the strength of the large-scale toroidal magnetic fields according to a local accretion rate. We also discuss a possible inner optically thin flow, the advection-dominated accretion flow (ADAF). This flow would require modification of the inner boundary condition of the cold disk flow. For the set of the global parameters, we calculated the variability timescales and outburst amplitudes of the disk and the corona. Results. We found that the role of the inner ADAF and the accreting corona are relatively unimportant, but the outburst character strongly depends on the magnetic field and on the outer radius of the disk if this radius is smaller (due to the TDE phenomenon) than the size of the instability zone in a stationary disk with infinite radius. For microquasars, the dependence on the magnetic field is monotonic, and the period decreases with the field strength. For higher black hole masses, the dependence is nonmonotonic, and an initial rise of the period is later replaced with a relatively rapid decrease as the magnetic field continues to rise. A still stronger magnetic field stabilizes the disk. When we assumed a smaller disk outer radiusfor 105 and 107 M⊙, the outbursts were shorter and led to complex multiscale outbursts for some parameters, thus approaching the behavior of deterministic chaos. Conclusions. Our computations confirm that the radiation pressure instability model can account for heartbeat states in microquasars. The rapid variability detected in intermediate-mass black holes in the form of quasi-periodic eruptions can be consistent with the model, but only when it is combined with the TDE phenomenon. The yearly repeating variability in changing-look active galactic nuclei in our model also requires a small outer radius either due to the recent TDE or due to the gap in the disk that is related to a secondary black hole.

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“…Thus, large spectral state changes in quasars challenge and invigorate debates about both accretion theory and the nature of historical quasar classes (i.e., type 1 versus type 2; Elitzur et al 2014). Some recent studies suggest that the timescale problem can be qualitatively alleviated when taking the large-scale magnetic field into account (Dexter & Begelman 2019;Pan et al 2021) or considering accretion disk instabilities (e.g., the radiation pressure instability; Sniegowska et al 2020).…”

Section: Introductionmentioning

confidence: 99%

Probing the Origin of Changing-look Quasar Transitions with Chandra

Yang,

Green,

MacLeod

et al. 2023

ApJ

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Extremely variable quasars can also show strong changes in broad-line emission strength and are known as changing-look quasars (CLQs). To study the CLQ transition mechanism, we present a pilot sample of CLQs with X-ray observations in both the bright and faint states. From a sample of quasars with bright-state archival SDSS spectra and (Chandra or XMM-Newton) X-ray data, we identified five new CLQs via optical spectroscopic follow-up and then obtained new target-of-opportunity X-ray observations with Chandra. No strong absorption is detected in either the bright- or the faint-state X-ray spectra. The intrinsic X-ray flux generally changes along with the optical variability, and the X-ray power-law slope becomes harder in the faint state. Large-amplitude mid-infrared variability is detected in all five CLQs, and it echoes the variability in the optical with a time lag expected from the light-crossing time of the dusty torus for CLQs with robust lag measurements. The changing-obscuration model is not consistent with the observed X-ray spectra and spectral energy distribution changes seen in these CLQs. It is highly likely that the observed changes are due to the changing accretion rate of the supermassive black hole, so the multiwavelength emission varies accordingly, with promising analogies to the accretion states of X-ray binaries.

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The Effects of Large-scale Magnetic Fields on the Model for Repeating Changing-look AGNs

Cited by 19 publications

References 62 publications

Deciphering the extreme X-ray variability of the nuclear transient eRASSt J045650.3−203750

Deciphering the extreme X-ray variability of the nuclear transient eRASSt J045650.3−203750

Modified models of radiation pressure instability applied to 10, 10⁵, and 10⁷ M_⊙ accreting black holes

Probing the Origin of Changing-look Quasar Transitions with Chandra

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The Effects of Large-scale Magnetic Fields on the Model for Repeating Changing-look AGNs

Cited by 19 publications

References 62 publications

Deciphering the extreme X-ray variability of the nuclear transient eRASSt J045650.3−203750

Deciphering the extreme X-ray variability of the nuclear transient eRASSt J045650.3−203750

Modified models of radiation pressure instability applied to 10, 105, and 107 M⊙ accreting black holes

Probing the Origin of Changing-look Quasar Transitions with Chandra

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Modified models of radiation pressure instability applied to 10, 10⁵, and 10⁷ M_⊙ accreting black holes