Hot Accretion Flows Around Black Holes

Yuan, Feng; Narayan, Ramesh

doi:10.1146/annurev-astro-082812-141003

Cited by 1,326 publications

(1,336 citation statements)

References 582 publications

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“…The accretion mode transition is mainly triggered by the dimensionless mass accretion rate ṁ (m M M criṫ˙= ), which depends sensitively on the viscosity parameter α (see Narayan et al 1998;Yuan & Narayan 2014, for reviews). The critical mass accretion rate m criṫ can be estimated by equating the ionelectron equilibration timescale to the accretion timescale of an advection-dominated accretion flow (ADAF; Narayan et al 1998).…”

Section: Introductionmentioning

confidence: 99%

An Accretion Disk-Outflow Model for Hysteretic State Transition in X-Ray Binaries

Cao

2016

ApJ

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We suggest a model of the advection-dominated accretion flow (ADAF) with magnetically driven outflows to explain the hysteretic state transition observed in X-ray binaries (XRBs). The transition from a thin disk to an ADAF occurs when the mass accretion rate is below a critical value. The critical mass accretion rate for the ADAF can be estimated by equating the equilibration timescale to the accretion timescale of the ADAF, which is sensitive to its radial velocity. The radial velocity of thin disks is very small, which leads to the advection of the external field in thin disks becoming very inefficient. ADAFs are present in the low/hard states of XRBs, and their radial velocity is large compared with the thin disk. The external field can be dragged inward efficiently by the ADAF, so a strong large-scale magnetic field threading the ADAF can be formed, which may accelerate a fraction of gas in the ADAF into the outflows. Such outflows may carry away a large amount of angular momentum from the ADAF, which significantly increases the radial velocity of the ADAF. This leads to a high critical mass accretion rate, below which an ADAF with magnetic outflows can survive. Our calculations show that the critical luminosity of the ADAF with magnetic outflows can be one order of magnitude higher than that for a conventional ADAF, if the ratio of gas to magnetic pressure 4 b~in the disk. This can naturally explain the hysteretic state transition observed in XRBs.

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Section: Introductionmentioning

confidence: 99%

An Accretion Disk-Outflow Model for Hysteretic State Transition in X-Ray Binaries

Cao

2016

ApJ

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“…The outflow can transport energy, momentum, mass, heavy elements from the accretion disc and/or the vicinity of central region to the host galaxy and IGM, which regulate the efficiency of accretion onto the central supermassive black hole (e.g., Emmering et al 1992;Konigl & Kartje 1994), and influence the evolution of the host galaxy and surrounding environment (e.g., Tremonti et al 2007;Cattaneo et al 2009;Yuan & Narayan 2014;Ishibashi & Fabian 2014). Intrinsic absorption lines, including BALs, mini-BALs and NALs, are often utilized to study properties of the quasar outflow.…”

Section: Introductionmentioning

confidence: 99%

Narrow absorption lines with two observations from the Sloan Digital Sky Survey

Chen¹,

Gu²,

Chen³

et al. 2015

Monthly Notices of the Royal Astronomical Society

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We assemble 3524 quasars from Sloan Digital Sky Survey (SDSS) with repeated observations to search for variations of narrow C IVλλ1548, 1551 and Mg IIλλ2796, 2803 absorption doublets in spectral regions shortward of 7000Å at the observed frame, which corresponds to time-scales of about 150 ∼ 2643 days at quasar rest frame. In these quasar spectra, we detect 3580 C IV absorption systems with z abs = 1.5188 ∼ 3.5212, and 1809 Mg II absorption systems with z abs = 0.3948 ∼ 1.7167. In term of the absorber velocity (β) distribution at quasar rest frame, we find a substantial number of C IV absorbers with β < 0.06, which might be connected to the absorptions of quasar outflows. The outflow absorptions peak at υ ≈ 2000 km s −1 and drop rapidly below the peak value. Among 3580 C IV absorption systems, 52 systems (∼ 1.5%) show obvious variations in equivalent widths at the absorber rest frame (W r ): 16 enhanced, 16 emerged, 12 weaken, and 8 disappeared systems, respectively. We find that changes in W r λ1548 are neither related to time-scales of the two SDSS observations, nor to absorber velocities at the quasar rest frame. Variable absorptions in low-ionization species are important to constraint the physical conditions of absorbing gas. There are two variable Mg II absorption systems measured from SDSS spectra detected by Hacker et al. However, in our Mg II absorption sample, we find that neither shows variable absorption with confident levels of > 4σ for λ2796 lines and > 3σ for λ2803 lines.

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“…During the low/hard state, defined as an accretion state in X-ray binaries dominated by a flat powerlaw emission and a strong band limited noise in the Fourier power spectra (Remillard & McClintock 2006), the inner part of the truncated disc is usually filled with a hot, relativistic electron plasma (Yuan & Narayan 2014) along with intense magnetic fields (Esin et al 1997). The idea that such magnetized hot flow could be the birthplace of optical photons by means of electron-cyclotron emission, was introduced by Fabian et al (1982) and successfully explained some of the fast variability observed from GX 339-4 (Motch et al 1983), 20-sec X-ray QPOs and the observed X-ray/optical anticorrelation in the CCF.…”

Section: Introductionmentioning

confidence: 99%

Simultaneous optical/X-ray study of GS 1354-64 (=BW Cir) during hard outburst: evidence for optical cyclo-synchrotron emission from the hot accretion flow

Pahari

Gandhi

Charles

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We present results from simultaneous optical (SALT) and X-ray (Swift and IN-TEGRAL) observations of GS 1354-64/BW Cir during the 2015 hard state outburst. During the rising phase, optical/X-ray time series show a strong anti-correlation with X-ray photons lagging optical. Optical and X-ray power spectra show quasi-periodic oscillations at a frequency of ∼ 18 mHz with a confidence level of at least 99%. Simultaneous fitting of Swift/XRT and INTEGRAL spectra in the range 0.5−1000.0 keV shows non-thermal, power-law dominated (> 90%) spectra with a hard powerlaw index of 1.48 ± 0.03, inner disc temperature of 0.12 ± 0.01 keV and inner disc radius of ∼3000 km. All evidence is consistent with cyclo-synchrotron radiation in a non-thermal, hot electron cloud extending to ∼ 100 Schwarzschild radii being a major physical process for the origin of optical photons. At outburst peak about one month later, when the X-ray flux rises and the optical drops, the apparent features in the optical/X-ray correlation vanish and the optical auto correlation widens. Although ∼0.19 Hz QPO is observed from the X-ray power spectra, the optical variability is dominated by the broadband noise, and the inner disc temperature increases. These results support a change in the dominant optical emission source between outburst rise and peak, consistent with a weakening of hot flow as the disc moves in.

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Hot Accretion Flows Around Black Holes

Cited by 1,326 publications

References 582 publications

An Accretion Disk-Outflow Model for Hysteretic State Transition in X-Ray Binaries

An Accretion Disk-Outflow Model for Hysteretic State Transition in X-Ray Binaries

Narrow absorption lines with two observations from the Sloan Digital Sky Survey

Simultaneous optical/X-ray study of GS 1354-64 (=BW Cir) during hard outburst: evidence for optical cyclo-synchrotron emission from the hot accretion flow

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