The Speed of Cooling Fronts and the Functional Form of the Dimensionless Viscosity in Accretion Disks

Vishniac, Ethan T.; Wheeler, J. C.

doi:10.1086/178019

Cited by 22 publications

(37 citation statements)

References 19 publications

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“…4 of Menou et al 1999a). The front propagates through the disc at a speed V front ≈ α h c s (Meyer 1984;Vishniac & Wheeler 1996). In the standard DIM, the sound speed depends on the temperature at the transition between the hot and cold regions and is almost constant as verified by numerical calculations (Menou et al 1999a).…”

Section: Irradiation-controlled Linear Decaymentioning

confidence: 82%

The disc instability model for X-ray transients: Evidence for truncation and irradiation

Dubus

Hameury

Lasota

2001

A&A

343

549

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Abstract.We study the prospect of explaining the outbursts of Soft X-ray Transients (SXTs) by the thermalviscous instability in a thin disc. This instability is linked to hydrogen ionization and is significantly changed when irradiation of the disc by X-rays from the inner regions is included. We present the first numerically reliable, physically consistent calculations of the outburst cycles which include the effects of accretion disc irradiation. The decay from outburst is governed by irradiation, as pointed out by King & Ritter (1998), leading to slow exponential decays. At the end of the outburst, the disc is severely depleted, which lengthens the time needed to rebuild mass to the critical density for an outburst. Despite this, the long recurrence times and quiescent X-ray luminosities of SXTs still require the inner disc to be replaced by another type of flow in quiescence, presumably a hot advection dominated accretion flow (ADAF). We include the effects of such truncation and show that the resulting lightcurves are conclusively similar to those of SXTs like A0620-00. We conclude that the two-α disc instability model provides an adequate description of the outbursts of SXTs when both truncation and irradiation are included. The values for the viscosities in outburst and in quiescence are comparable to those used in CVs. We discuss the model in the context of present observations.

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Section: Irradiation-controlled Linear Decaymentioning

confidence: 82%

The disc instability model for X-ray transients: Evidence for truncation and irradiation

Dubus

Hameury

Lasota

2001

A&A

343

549

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“…The transition is triggered by a heating wave propagating through the disc. The transition wave velocity v tr ∼ αc s (H/r) 0.5 (Vishniac & Wheeler 1996) is a few times higher than the radial velocity of the matter in the disc v R ∼ αc s H/r, where c s ≈ 10 6 (T/10 4 K) 1/2 cm s −1 is the local sound speed, α ∼ 0.01 − 0.1 is a viscosity parameter, and H is a local disc half thickness. We assume α = 0.1 for all subsequent estimates.…”

Section: Accretion Disc Instabilitymentioning

confidence: 99%

Propeller effect in two brightest transient X-ray pulsars: 4U 0115+63 and V 0332+53

Tsygankov

Lutovinov

Doroshenko

et al. 2016

A&A

103

111

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Aims. We present the results of the monitoring programmes performed with the Swift/XRT telescope and aimed specifically to detect an abrupt decrease of the observed flux associated with a transition to the propeller regime in two well-known X-ray pulsars 4U 0115+63 and V 0332+53. Methods. Both sources form binary systems with Be optical companions and undergo so-called giant outbursts every 3-4 years. The current observational campaigns were performed with the Swift/XRT telescope in the soft X-ray band (0.5-10 keV) during the declining phases of the outbursts exhibited by both sources in 2015.Results. The transitions to the propeller regime were detected at the threshold luminosities of (1.4 ± 0.4) × 10 36 erg s −1 and (2.0 ± 0.4) × 10 36 erg s −1 for 4U 0115+63 and V 0332+53, respectively. Spectra of the sources are shown to be significantly softer during the low state. In both sources, the accretion at rates close to the aforementioned threshold values briefly resumes during the periastron passage following the transition into the propeller regime. The strength of the dipole component of the magnetic field required to inhibit the accretion agrees well with estimates based on the position of the cyclotron lines in their spectra, thus excluding presence of a strong multipole component of the magnetic field in the vicinity of the neutron star.

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“…Numerical modelling of DIM in dwarf novae shows that, if α hot is constant, the speed of the cooling front approaches a characteristic constant velocity of order of α hot u sound (Meyer 1984;Cannizzo 1994;Vishniac & Wheeler 1996), with the hot inner part of the disk evolving in a self-similar way (Menou et al 1999).…”

Section: Cooling Front Without Irradiationmentioning

confidence: 99%

Determination of the turbulent parameter in accretion discs: effects of self-irradiation in 4U 1543−47 during the 2002 outburst

Lipunova

Malanchev

2017

Monthly Notices of the Royal Astronomical Society

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We investigate the viscous evolution of the accretion disk in 4U 1543−47, a black hole binary system, during the first 30 days after the peak of the 2002 burst by comparing the observed and theoretical accretion rate evolutionṀ(t). The observedṀ(t) is obtained from spectral modelling of the archival RXTE/PCA data. Different scenarios of disk decay evolution are possible depending on a degree of self-irradiation of the disk by the emission from its centre. If the self-irradiation, which is parametrized by factor C irr , had been as high as ∼ 5 × 10 −3 , then the disk would have been completely ionized up to the tidal radius and the short time of the decay would have required the turbulent parameter α ∼ 3. We find that the shape of theṀ(t) curve is much better explained in a model with a shrinking high-viscosity zone. If C irr ≈ (2 − 3) × 10 −4 , the resulting α lie in the interval 0.5 − 1.5 for the black hole masses in the range 6 − 10 M , while the radius of the ionized disk is variable and controlled by irradiation. For very weak irradiation, C irr < 1.5 × 10 −4 , the burst decline develops as in normal outbursts of dwarf novae with α ∼ 0.08 − 0.32. The optical data indicate that C irr in 4U 1543−47 (2002) was not greater than approximately (3−6)×10 −4 . Generally, modelling of an X-ray nova burst allows one to estimate α that depends on the black hole parameters. We present the public 1-D code freddi to model the viscous evolution of an accretion disk. Analytic approximations are derived to estimate α in X-ray novae usingṀ(t).

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The Speed of Cooling Fronts and the Functional Form of the Dimensionless Viscosity in Accretion Disks

Cited by 22 publications

References 19 publications

The disc instability model for X-ray transients: Evidence for truncation and irradiation

The disc instability model for X-ray transients: Evidence for truncation and irradiation

Propeller effect in two brightest transient X-ray pulsars: 4U 0115+63 and V 0332+53

Determination of the turbulent parameter in accretion discs: effects of self-irradiation in 4U 1543−47 during the 2002 outburst

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