The pattern of accretion flow on to Sgr A

Mościbrodzka, Monika; Das, Tapas K.

doi:10.1111/j.1365-2966.2006.10470.x

Cited by 47 publications

(59 citation statements)

References 71 publications

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“…Despite this fact, the very occurrence of the flares and the minute time-scale of their rise and decay indicate that the immediate neighbourhood of the black hole is not entirely empty; likely, episodic accretion takes place. In fact, Moscibrodzka et al (2006) suggest that a transient torus develops at a distance of a few or a few ten gravitational radii and exists for several dynamical periods. The inner disk/torus is subject to violent instabilities, but it is difficult to identify the dominant mechanism responsible causing its destruction.…”

Section: The Hot Spot/ring Modelmentioning

confidence: 99%

Near-infrared polarimetry setting constraints on the orbiting spot model for Sgr A* flares

Meyer¹,

Eckart²,

Schödel³

et al. 2006

A&A

111

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Context. Recent near-infrared polarization measurements of Sgr A* show that its emission is significantly polarized during flares and consists of a non-or weakly polarized main flare with highly polarized sub-flares. The flare activity suggests a quasi-periodicity of ∼20 min in agreement with previous observations. Aims. By simultaneous fitting of the lightcurve fluctuations and the time-variable polarization angle, we address the question of whether these changes are consistent with a simple hot spot/ring model, in which the interplay of relativistic effects plays the major role, or whether some more complex dependency of the intrinsic emissivity is required. Methods. We discuss the significance of the 20 min peak in the periodogram of a flare from 2003. We consider all general relativistic effects that imprint on the polarization degree and angle and fit the recent polarimetric data, assuming that the synchrotron mechanism is responsible for the intrinsic polarization and considering two different magnetic field configurations. Results. Within the quality of the available data, we think that the model of a single spot in addition to an underlying ring is favoured. In this model the broad near-infrared flares of Sgr A* are due to a sound wave that travels around the MBH once while the sub-flares, superimposed on the broad flare, are due to transiently heated and accelerated electrons which can be modeled as a plasma blob. Within this model it turns out that a strong statement about the spin parameter is difficult to achieve, while the inclination can be constrained to values > ∼ 35• on a 3σ level.

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Section: The Hot Spot/ring Modelmentioning

confidence: 99%

Near-infrared polarimetry setting constraints on the orbiting spot model for Sgr A* flares

Meyer¹,

Eckart²,

Schödel³

et al. 2006

A&A

111

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“…The estimated angular momentum is based on the models of winds from emitting stars and depends on the assumptions. Recently, several papers have been published where the low angular momentum model for Sgr A* accretion was proposed and the amount of angular momentum from wind of the Wolf-Rayet star IRS 13 E3 was estimated to have quite low values λ ∈ (1.68÷2.16) R Schw c ∼ (3.36÷4.32)M (Mościbrodzka et al 2006;Okuda & Molteni 2012). However, other 3D simulations show considerably higher values of angular momentum of stellar wind at the Bondi radius ∼ 10 4 M (Cuadra et al 2008;Yuan & Narayan 2014).…”

Section: Introductionmentioning

confidence: 99%

Oscillating shocks in the low angular momentum flows as a source of variability of accreting black holes

Suková

Janiuk

2014

Monthly Notices of the Royal Astronomical Society

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We derive the conditions for shock formation in a quasi-spherical, slightly rotating flows. We verify the results of semi-analytical, stationary calculations with the time evolution studied by numerical hydro-simulations, and we study the oscillations of the shock position. We also study the behaviour of flows with varying specific angular momentum, where the 'hysteresis' type of loop is found when passing through the multiple sonic points region. Our results are in agreement with the timescales and shapes of the luminosity flares observed in Sgr A*. These models may also be applicable for the Galactic stellar mass black holes, like GX 339-4 or GRS 1915+105, where periodic oscillations of X-ray luminosity are detected.

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“…The standard model have been proven to be successful in studying the cataclysmic variables and later for neutron stars and black holes. However, for highly luminous accretion discs whose luminosity exceeds ⋆ E-mail:bbnbh669@ybb.ne.jp † E-mai: sbdas@iitg.ernet.in the Eddington luminosity as is found in the black hole candidate SS 433 or for very low luminous discs compared with the predicted accretion rate as the case of the supermassive black hole candidate Sgr A*, the S-S model is not valid and alternative thick disc models, such as the slim disc model ( Abramowicz et al 1988), the advection-dominated accretion disc model (Narayan & Yi 1994, 1995 and the low angular momentum disc model (Mościbrodzka, Das & Czerny 2006;Czerny & Mościbrodzka 2008), have been developed.…”

Section: Introductionmentioning

confidence: 99%

Unstable mass-outflows in geometrically thick accretion flows around black holes

Okuda¹,

Das

2015

Mon. Not. R. Astron. Soc.

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Accretion flows around black holes generally result in mass-outflows that exhibit irregular behavior quite often. Using 2D time-dependent hydrodynamical calculations, we show that the mass-outflow is unstable in the cases of thick accretion flows such as the low angular momentum accretion flow and the advection-dominated accretion flow. For the low angular momentum flow, the inward accreting matter on the equatorial plane interacts with the outflowing gas along the rotational axis and the centrifugally supported oblique shock is formed at the interface of both the flows, when the viscosity parameter α is as small as α 10 −3 . The hot and rarefied blobs, which result in the eruptive mass-outflow, are generated in the inner shocked region and grow up toward the outer boundary. The advection-dominated accretion flow attains finally in the form of a torus disc with the inner edge of the disc at 3R g r 6R g and the center at 6R g r 10R g , and a series of hot blobs is intermittently formed near the inner edge of the torus and grows up along the outer surface of the torus. As a result, the luminosity and the mass-outflow rate are modulated irregularly where the luminosity is enhanced by 10−40% and the mass-outflow rate is increaed by a factor of few up to ten. We interpret the unstable nature of the outflow to be due to the KelvinHelmholtz instability, examining the Richardson number for the Kelvin-Helmholtz criterion in the inner region of the flow. We propose that the flare phenomena of Sgr A* may be induced by the unstable mass-outflow as is found in this work.

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The pattern of accretion flow on to Sgr A

Cited by 47 publications

References 71 publications

Near-infrared polarimetry setting constraints on the orbiting spot model for Sgr A* flares

Near-infrared polarimetry setting constraints on the orbiting spot model for Sgr A* flares

Oscillating shocks in the low angular momentum flows as a source of variability of accreting black holes

Unstable mass-outflows in geometrically thick accretion flows around black holes

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