SPH simulations of Shakura-Sunyaev instability at intermediate accretion rates

Teresi, V.; Molteni, D.; Toscano, Elena

doi:10.1111/j.1365-2966.2004.07384.x

Cited by 12 publications

(7 citation statements)

References 18 publications

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“…Although, in this model, a high‐velocity jet with 0.2–0.4 c is formed along the rotational axis, the small collimation angle of ∼0.1 radian of the jets and a sufficient mass‐outflow rate comparable to ∼10 19 g s −1 could not be obtained. Additionally, it was also suggested that this result might be transient behaviour during a long disc evolution (Teresi, Molteni & Toscano 2004). Keeping these facts in mind, we further examine super‐Eddington accretion discs and jets around the black hole extending from the inner disc edge to 5 × 10 4 r g .…”

Section: Introductionmentioning

confidence: 98%

Black hole accretion discs and jets at super-Eddington luminosity

Okuda

Teresi

Toscano

et al. 2005

Monthly Notices of the Royal Astronomical Society

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Super-Eddington accretion discs with 3M ̇ E and 15M ̇ E around black holes with mass 10 M⊙ are examined by two-dimensional radiation hydrodynamical calculations extending from the inner disc edge to 5 × 104rg and lasting up to ∼106 rg/c. The dominant radiation pressure force in the inner region of the disc accelerates the gas vertically to the disc plane, and jets with 0.2–0.4c are formed along the rotational axis. In the case of the lower accretion rate, the initially anisotropic high-velocity jet expands outward and becomes gradually isotropic flow in the distant region. The mass-outflow rate from the outer boundary is as large as ∼1019 –1023 g s−1, but it is variable and intermittent with time; that is, the outflow switches occa- sionally to inflow in the distant region. The luminosity also varies as ∼1040–1042 erg s−1 on a long time-scale. On the other hand, the jet in the case of the higher accretion rate maintains its initial anisotropic shape even after it goes far away. The mass-outflow rate and the luminosity attain steady values of 3 × 1019 g s−1 and 1.3 × 1040 erg s−1, respectively. In accordance with the local analysis of the slim accretion disc model, the disc is thermally unstable in the case of 3M ̇ E but stable in the case of 15M ̇ E. The super-Eddington model with 15M ̇ E promises to explain the small collimation degree of the jet and the large mass-outflow rate observed in the X-ray source SS 433

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Section: Introductionmentioning

confidence: 98%

Black hole accretion discs and jets at super-Eddington luminosity

Okuda

Teresi

Toscano

et al. 2005

Monthly Notices of the Royal Astronomical Society

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“…Teresi, Molteni & Toscano (2004) have clearly shown that, at intermediate accretion rates, accretion discs with A zone suffer a collapse but after a rather long time they show a flaring activity with an intervening refilling phase of the A zone.…”

Section: Introductionmentioning

confidence: 99%

Ab initiosimulations of accretion disc instability

Teresi

Molteni

Toscano

2004

Monthly Notices of the Royal Astronomical Society

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We show that accretion discs, both in the subcritical and supercritical accretion rate regime, may exhibit significant amplitude luminosity oscillations. The luminosity time behaviour has been obtained by performing a set of time-dependent two-dimensional smoothed particle hydrodynamics simulations of accretion discs with different values of α and accretion rate. In this study, to avoid any influence of the initial disc configuration, we produced the discs injecting matter from an outer edge far from the central object. The period of oscillations is 2-50 s for the two cases, and the variation amplitude of the disc luminosity is 10 38 -10 39 erg s −1 . An explanation of this luminosity behaviour is proposed in terms of limit cycle instability; the disc oscillates between a radiation pressure dominated configuration (with a high luminosity value) and a gas pressure dominated one (with a low luminosity value). The origin of this instability is the difference between the heat produced by viscosity and the energy emitted as radiation from the disc surface (the well-known thermal instability mechanism). We support this hypothesis showing that the limit cycle behaviour produces a sequence of collapsing and refilling states of the innermost disc region.

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“…Recently, Teresi et al (2004aTeresi et al ( , 2004b first reproduced the quasiperiodic luminosity variations using two-dimensional smoothed particle hydrodynamic (SPH) simulations. However, their simulations focused on the time evolution of the disk itself and do not treat the optically thin regime correctly, i.e., the disk surface as well as the atmosphere surrounding the disk.…”

Section: Introductionmentioning

confidence: 99%

Two‐dimensional Radiation‐Hydrodynamic Model for Limit‐Cycle Oscillations of Luminous Accretion Disks

Ohsuga

2006

ApJ

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We investigate the time evolution of luminous accretion disks around black holes by conducting two-dimensional radiation-hydrodynamic simulations. We adopt the prescription for the viscosity. The radial-azimuthal component of the viscous stress tensor is assumed to be proportional to the total pressure in the optically thick region and the gas pressure in the optically thin regime. The viscosity parameter, , is taken to be 0.1. We find the limit-cycle variation in luminosity between high and low states. When we set the mass input rate from the outer disk boundary to be 100L E /c 2 , the luminosity suddenly rises from 0:3L E to 2L E , where L E is the Eddington luminosity. It decays after retaining the high value for about 40 s. Our numerical results can explain the variability amplitude and duration of the recurrent outbursts observed in microquasar GRS 1915+105. We show that multidimensional effects play an important role in the high-luminosity state. In this state, the outflow is driven by the strong radiation force, and some part of the radiation energy dissipated inside the disk is swallowed by the black hole due to the photon-trapping effects. This trapped luminosity is comparable to the disk luminosity. We also calculate two more cases: one with a much larger accretion rate than the critical value for the instability and the other with the viscous stress tensor being proportional to the gas pressure only, even when the radiation pressure is dominant. We find no quasi-periodic light variations in these cases. This confirms that the limit-cycle behavior found in the simulations is caused by the disk instability.

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SPH simulations of Shakura-Sunyaev instability at intermediate accretion rates

Cited by 12 publications

References 18 publications

Black hole accretion discs and jets at super-Eddington luminosity

Black hole accretion discs and jets at super-Eddington luminosity

Ab initiosimulations of accretion disc instability

Two‐dimensional Radiation‐Hydrodynamic Model for Limit‐Cycle Oscillations of Luminous Accretion Disks

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