Extreme AGN variability: evidence of magnetically elevated accretion?

Dexter, Jason; Begelman, Mitchell C.

doi:10.1093/mnrasl/sly213

Cited by 108 publications

(98 citation statements)

References 71 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…More clearly, we propose the appearance of the broad Hα component in the bright AGN regime and disappearance of the broad Hα component in the LLAGN regime. We note that similar scenarios have been proposed in the literature (Noda & Done 2018;Dexter & Begelman 2019a;Ruan et al 2019), although the on-off timescale in CL-AGNs remains a challenging task in this model (Dexter & Begelman 2019a). Based on broadband continuum spectral modeling Noda & Done (2018) suggest that Mrk 1018 underwent a soft-to-hard state transition as it faded from Seyfert 1 to 1.9.…”

Section: Nature Of the Variabilitysupporting

confidence: 64%

X-Ray Spectral Shape Variation in Changing-look Seyfert Galaxy SDSS J155258+273728

Dou

Yang

et al. 2020

ApJL

View full text Add to dashboard Cite

We analyze the X-ray, optical, and mid-infrared data of a "changing-look" Seyfert galaxy SDSS J155258+273728 at z;0.086. Over a period of one decade (2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018), its broad Hα line intensity increased by a factor of ∼4. Meanwhile, the X-ray emission in 2014 as observed by Chandra was about five times brighter than that in 2010 by Suzaku, and the corresponding emissions in the V-band, mid-infrared W1 band brighten by ∼0.18, 0.32 mag, respectively. Moreover, the absorption in X-rays is moderate and stable, i.e.,~-N 10 cm H 21 2 , but the X-ray spectrum becomes harder in the 2014 Chandra bright state (i.e., photon index G = -+ 1.52 0.06 0.06 ) than that of the 2010 Suzaku low state (G = -+ 2.03 0.21 0.22 ). With an Eddington ratio being lower than a few percent, the inner region of the accretion disk in SDSS J155258+273728is likely a hot accretion flow. We then compile from literature the X-ray data of "changing-look" active galactic nuclei (AGNs), and find that they generally follow the well-established "V"-shaped correlation in AGNs, that is, above a critical turnover luminosity the X-ray spectra soften with the increasing luminosity, and below that luminosity the trend is reversed in the way of "harder when brighter." This presents direct evidence that CL-AGNs have distinctive changes in not only the optical spectral type, but also the X-ray spectral shape. The similarity in the X-ray spectral evolution between CL-AGNs and black hole X-ray binaries indicates that the observed CL-AGNs phenomena may relate to the state transition in accretion physics.

show abstract

Section: Nature Of the Variabilitysupporting

confidence: 64%

X-Ray Spectral Shape Variation in Changing-look Seyfert Galaxy SDSS J155258+273728

Dou

Yang

et al. 2020

ApJL

View full text Add to dashboard Cite

show abstract

“…150 R g ) in NGC 7589, a H/R ∼ 0.05 is required so that the predicted viscosity time-scale (4 years for a disc with α = 0.5) matches with the estimated t ADAF→TD (a few years) for NGC 7589. Although such a large H/R is not expected in the thin disc model (H/R should be ∼ 10 −3 ), it can be obtained in the magnetic pressure supported accretion disc model proposed by (Dexter & Begelman 2019). In this model, the disc is geometrically thick at all luminosities which gives a viscous propagation time-scale as short as a few years, consistent with the observed time-scale.…”

Section: Transition From Low State To High Statesupporting

confidence: 76%

The large amplitude X-ray variability in NGC 7589: possible evidence for accretion mode transition

Liu

Cheng

et al. 2019

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

We report the discovery of large amplitude X-ray variability in the low luminosity AGN (LLAGN) NGC 7589, and present possible observational evidence for accretion mode transition in this source. Long-term X-ray flux variations by a factor of more than 50 are found using X-ray data obtained by Swift/XRT and XMM-Newton over 17 years. Results of long-term monitoring data in the UV, optical and infrared bands over ∼ 20 years are also presented. The Eddington ratio λ Edd increased from 10 −3 to ∼ 0.13, suggesting a transition of the accretion flow from an ADAF to a standard thin accretion disc. Further evidence supporting the thin disc in the high luminosity state is found by the detection of a significant soft X-ray component in the X-ray spectrum. The temperature of this component (∼ 19 +15 −7 eV, fitted with a blackbody model) is in agreement with the predicted temperature of the inner region for a thin disc around a black hole (BH) with mass of ∼ 10 7 M . These results may indicate that NGC 7589 had experienced accretion mode transition over a timescale of a few years, suggesting the idea that similar accretion processes are at work for massive black hole and black hole X-ray binaries.

show abstract

“…Begelman & Silk 2017, and references therein) and not only in the upper layers (e.g. Miller & Stone 2000), possibly solving a few long-standing issues of the standard accretions disk theory (Dexter & Begelman 2019). Simulations indeed showed that P mag can become an important competitor in supporting the disk vertically (Bai & Stone 2013;Salvesen et al 2016), although heavily depending on the strength of the net vertical magnetic field, the origin of which is not fully understood, yet.…”

Section: Magnetically-dominated Disksmentioning

confidence: 98%

Testing the disk-corona interplay in radiatively-efficient broad-line AGN

Arcodia

Merloni

Nandra

et al. 2019

A&A

View full text Add to dashboard Cite

The correlation observed between monochromatic X-ray and UV luminosities in radiatively-efficient active galactic nuclei (AGN) lacks a clear theoretical explanation despite being used for many applications. Such a correlation, with its small intrinsic scatter and its slope that is smaller than unity in log space, represents the compelling evidence that a mechanism regulating the energetic interaction between the accretion disk and the X-ray corona must be in place. This ensures that going from fainter to brighter sources the coronal emission increases less than the disk emission. We discuss here a self-consistently coupled disk-corona model that can identify this regulating mechanism in terms of modified viscosity prescriptions in the accretion disk. The model predicts a lower fraction of accretion power dissipated in the corona for higher accretion states. We then present a quantitative observational test of the model using a reference sample of broad-line AGN and modeling the disk-corona emission for each source in the L X − L UV plane. We used the slope, normalization, and scatter of the observed relation to constrain the parameters of the theoretical model. For non-spinning black holes and static coronae, we find that the accretion prescriptions that match the observed slope of the L X − L UV relation produce X-rays that are too weak with respect to the normalization of the observed relation. Instead, considering moderatelyoutflowing Comptonizing coronae and/or a more realistic high-spinning black hole population significantly relax the tension between the strength of the observed and modeled X-ray emission, while also predicting very low intrinsic scatter in the L X − L UV relation. In particular, this latter scenario traces a known selection effect of flux-limited samples that preferentially select high-spinning, hence brighter, sources.

show abstract

Extreme AGN variability: evidence of magnetically elevated accretion?

Cited by 108 publications

References 71 publications

X-Ray Spectral Shape Variation in Changing-look Seyfert Galaxy SDSS J155258+273728

X-Ray Spectral Shape Variation in Changing-look Seyfert Galaxy SDSS J155258+273728

The large amplitude X-ray variability in NGC 7589: possible evidence for accretion mode transition

Testing the disk-corona interplay in radiatively-efficient broad-line AGN

Contact Info

Product

Resources

About