Instability of an accretion disk with a magnetically driven wind

Cao, Xinwu; Spruit, H. C.

doi:10.1051/0004-6361:20011818

Cited by 50 publications

(64 citation statements)

References 21 publications

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“…In that case, they suggested, there is the possibility for a wind-driven avalanche which could sweep the inner disk regions inwards. Cao & Spruit (2002) and Campbell (2009) concur with this conclusion. An example of how such an avalanche might operate is to be found in the numerical simulations by Lovelace et al (1994).…”

Section: Large Amplitude Variabilitysupporting

confidence: 72%

Extreme variability in an active galactic nucleus: Gaia16aax

Cannizzaro

Fraser

Jonker

et al. 2020

Monthly Notices of the Royal Astronomical Society

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We present the results of a multi-wavelength follow up campaign for the luminous nuclear transient Gaia16aax, which was first identified in January 2016. The transient is spatially consistent with the nucleus of an active galaxy at z=0.25, hosting a black hole of mass ∼ 6 × 10 8 M . The nucleus brightened by more than 1 magnitude in the Gaia G-band over a timescale of less than one year, before fading back to its preoutburst state over the following three years. The optical spectra of the source show broad Balmer lines similar to the ones present in a pre-outburst spectrum. During the outburst, the Hα and Hβ emission lines develop a secondary peak. We also report on the discovery of two transients with similar light curve evolution and spectra: Gaia16aka and Gaia16ajq. We consider possible scenarios to explain the observed outbursts. We exclude that the transient event could be caused by a microlensing event, variable dust absorption or a tidal encounter between a neutron star and a stellar mass black hole in the accretion disk. We consider variability in the accretion flow in the inner part of the disk, or a tidal disruption event of a star ≥ 1M by a rapidly spinning supermassive black hole as the most plausible scenarios. We note that the similarity between the light curves of the three Gaia transients may be a function of the Gaia alerts selection criteria.

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Section: Large Amplitude Variabilitysupporting

confidence: 72%

Extreme variability in an active galactic nucleus: Gaia16aax

Cannizzaro

Fraser

Jonker

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…The accretion disc may be vertically compressed by the advected large scale magnetic field (Cao & Spruit 2002;Cao 2011). This may also be the case for the corona case discussed in this paper.…”

Section: Resultsmentioning

confidence: 75%

The power of the jets accelerated by the coronal magnetic field

Cao

2017

Monthly Notices of the Royal Astronomical Society

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It was suggested that the large scale magnetic field can be dragged inwards efficiently by the corona above the disc, i.e., the so called "coronal mechanism" (Beckwith, Hawley, & Krolik 2009), which provides a way to solve the difficulty of field advection in a geometrically thin accretion disc. In this case, the magnetic pressure should be lower than the gas pressure in the corona. We estimate the maximal power of the jets accelerated by the magnetic field advected by the corona. The Blandford-Payne (BP) jet power is found always to be higher than the Blandford-Znajek (BZ) jet power, except for a rapidly spinning black hole with a 0.8. The maximal jet power is always low, less than 0.05 Eddington luminosity, even for an extreme Kerr black hole, which is insufficient for the observed strong jets in some blazars with jet power ∼ 0.1 − 1 Eddington luminosity (or even higher). It implies that these powerful jets cannot be accelerated by the coronal field. We suggest that, the magnetic field dragged inward by the accretion disc with magnetically outflows may accelerate the jets (at least for the most powerful jets, if not all) in the blazars.

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“…The final results on the advection of the fields in the NDAFs are found to be insensitive to the value of γ adopted. The accretion flow is vertically compressed by the strong large-scale magnetic fields (Cao & Spruit 2002;Cao 2011). Assuming the pressure gradient to be in equilibrium with gravity in the vertical direction of the accretion flow, the vertical structure of the disk can be described by dp(z) dz…”

Section: Structure Of the Ndafmentioning

confidence: 99%

“…is proposed, where H is the scale height of the disk (defined as ρ(H ) = ρ(0) exp(−1/2)), the field line inclination κ 0 = B z /B S R at z = H , and η i = tanh(1) (Cao & Spruit 2002). The main features of the Kippenhahn-Schlüter model (Kippenhahn & Schlüter 1957) can be well reproduced by this expression either for weak or strong field cases.…”

Section: Structure Of the Ndafmentioning

confidence: 99%

Episodic Jet Power Extracted From a Spinning Black Hole Surrounded by a Neutrino-Dominated Accretion Flow in Gamma-Ray Bursts

Cao¹,

Liang²,

Yuan³

2014

ApJ

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It was suggested that the relativistic jets in gamma-ray bursts (GRBs) are powered via the Blandford-Znajek (BZ) mechanism or the annihilation of neutrinos and anti-neutrinos from a neutrino cooling-dominated accretion flow (NDAF). The advection and diffusion of the large-scale magnetic field of an NDAF is calculated, and the external magnetic field is found to be dragged inward efficiently by the accretion flow for a typical magnetic Prandtl number P m = η/ν ∼ 1. The maximal BZ jet power can be ∼10 53 -10 54 erg s −1 for an extreme Kerr black hole, if an external magnetic field with 10 14 Gauss is advected by the NDAF. This is roughly consistent with the field strength of the disk formed after a tidal disrupted magnetar. The accretion flow near the black hole horizon is arrested by the magnetic field if the accretion rate is below than a critical value for a given external field. The arrested accretion flow fails to drag the field inward and the field strength decays, and then the accretion re-starts, which leads to oscillating accretion. The typical timescale of such episodic accretion is of an order of one second. This can qualitatively explain the observed oscillation in the soft extended emission of short-type GRBs.

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Instability of an accretion disk with a magnetically driven wind

Cited by 50 publications

References 21 publications

Extreme variability in an active galactic nucleus: Gaia16aax

Extreme variability in an active galactic nucleus: Gaia16aax

The power of the jets accelerated by the coronal magnetic field

Episodic Jet Power Extracted From a Spinning Black Hole Surrounded by a Neutrino-Dominated Accretion Flow in Gamma-Ray Bursts

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