INFLOW-OUTFLOW MODEL WITH CONDUCTION AND SELF-CONSISTENT FEEDING FOR Sgr A*

Shcherbakov, Roman V.; Baganoff, Frederick K.

doi:10.1088/0004-637x/716/1/504

Cited by 88 publications

(140 citation statements)

References 35 publications

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“…OurṀ = 4.5 × 10 −8 M yr −1 (see Table 1) is consistent withṀ = 6 × 10 −8 M yr −1 found in models where the BH is fed by stellar winds (Shcherbakov & Baganoff 2010, but see Quataert 2004, and with estimates by Sharma et al (2007) based on local collisionless plasma models. A higherṀ may also change expectations for the recently discovered cloud-like object G2 that moves toward Sgr A* (Gillessen et al 2012), which is expected to be accreted onto the BH soon.…”

Section: Discussionsupporting

confidence: 90%

Coupled jet-disk model for Sagittarius A*: explaining the flat-spectrum radio core with GRMHD simulations of jets

Mościbrodzka

Falcke

2013

A&A

123

146

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Context. The supermassive black hole in the center of the Milky Way, Sgr A*, displays a nearly flat radio spectrum that is typical for jets in active galactic nuclei. Indeed, time-dependent magnetized models of radiatively inefficient accretion flows (RIAFs), which are commonly used to explain the millimeter, near-infrared, and X-ray emission of Sgr A*, often also produce jet-like outflows. However, the emission from these models has so far failed to reproduce the flat radio spectrum. Aims. We investigate whether current accretion simulations can produce the compact flat spectrum emission by simply using a different prescription for the heating of the radiating particles in the jet. Methods. We studied the radiative properties of accretion flows onto a black hole produced in time-dependent general-relativistic magnetohydrodynamic (GRMHD) simulations. A crucial free parameter in these models has always been the electron temperature, and here we allowed for variations in the proton-to-electron temperature ratios in the jet and disk. Results. We found that the flat spectrum is readily reproduced by a standard GRMHD model if one has an almost isothermal jet coupled to a two-temperature accretion flow. The low-frequency radio emission comes from the outflowing sheath of matter surrounding the strongly magnetized nearly empty jet. The model is consistent with the radio sizes and spectrum of Sgr A*. Conclusions. Hence, GRMHD models of accreting black holes can in principle naturally reproduce jets that match observed characteristics. For Sgr A* the model fit to the spectrum predicts higher mass-accretion rates when a jet is included than without a jet. Hence, the impact of the recently discovered G2 cloud that is expected to be accreted onto Sgr A* might be less severe than currently thought.

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Section: Discussionsupporting

confidence: 90%

Coupled jet-disk model for Sagittarius A*: explaining the flat-spectrum radio core with GRMHD simulations of jets

Mościbrodzka

Falcke

2013

A&A

123

146

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“…We found, however, that our results depended very strongly on the assumed power-law indices of the density and temperature profiles as well as on the choice of the point at which the extrapolation matched the numerical solutions. Instead of following this approach, we opt to use the result of Shcherbakov & Baganoff (2010, see also the discussion in Neilsen et al 2013) that 10% of the quiescent X-ray flux from Sgr A* originates in a point source and attribute 10% of the observed flux to the emission from our simulated volume.…”

Section: Current Spectral and Imagingmentioning

confidence: 99%

THE POWER OF IMAGING: CONSTRAINING THE PLASMA PROPERTIES OF GRMHD SIMULATIONS USING EHT OBSERVATIONS OF Sgr A*

Chan

Psaltis

Özel

et al. 2015

ApJ

139

162

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Recent advances in general relativistic magnetohydrodynamic simulations have expanded and improved our understanding of the dynamics of black-hole accretion disks. However, current simulations do not capture the thermodynamics of electrons in the low density accreting plasma. This poses a significant challenge in predicting accretion flow images and spectra from first principles. Because of this, simplified emission models have often been used, with widely different configurations (e.g., disk-versus jet-dominated emission), and were able to account for the observed spectral properties of accreting black holes. Exploring the large parameter space introduced by such models, however, requires significant computational power that exceeds conventional computational facilities. In this paper, we use GRay, a fast graphics processing unit (GPU) based ray-tracing algorithm, on the GPU cluster El Gato, to compute images and spectra for a set of six general relativistic magnetohydrodynamic simulations with different magnetic field configurations and black-hole spins. We also employ two different parametric models for the plasma thermodynamics in each of the simulations. We show that, if only the spectral properties of Sgr A * are used, all 12 models tested here can fit the spectra equally well. However, when combined with the measurement of the image size of the emission using the Event Horizon Telescope, current observations rule out all models with strong funnel emission, because the funnels are typically very extended. Our study shows that images of accretion flows with horizon-scale resolution offer a powerful tool in understanding accretion flows around black holes and their thermodynamic properties.

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“…Falcke & Markoff (2000) find a field strength of ∼25 G for the foot point of a hypothetical jet. Estimates from relativistic MHD simulations result in values in the range of 30−50 G (Moscibrodzka et al 2009;Dexter et al 2010;Shcherbakov & Baganoff 2010).…”

Section: The Magnetic Field Strength Bmentioning

confidence: 99%

Millimeter to X-ray flares from Sagittarius A*

Eckart

García-Marín

Vogel

et al. 2012

A&A

146

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Context. We report on new simultaneous observations and modeling of the millimeter, near-infrared, and X-ray flare emission of the source Sagittarius A* (SgrA*) associated with the super-massive (4 × 10 6 M ) black hole at the Galactic center. Aims. We study the applicability of the adiabatic synchrotron source expansion model and study physical processes giving rise to the variable emission of SgrA* from the radio to the X-ray domain. Methods. Our observations were carried out on 18 May 2009 using the NACO adaptive optics (AO) instrument at the European Southern Observatory's Very Large Telescope, the ACIS-I instrument aboard the Chandra X-ray Observatory, the LABOCA bolometer at the Atacama Pathfinder EXperiment (APEX), and the CARMA mm telescope array at Cedar Flat, California. Results. The X-ray flare had an excess 2−8 keV luminosity between 6 and 12×10 33 erg s −1 . The observations reveal flaring activity in all wavelength bands that can be modeled as the signal from an adiabatically expanding synchrotron self-Compton (SSC) component.Modeling of the light curves shows that the sub-mm follows the NIR emission with a delay of about three-quarters of an hour with an expansion velocity of about v exp ∼ 0.009c. We find source component sizes of around one Schwarzschild radius, flux densities of a few Janskys, and spectral indices α of about +1 (S (ν) ∝ ν −α ). At the start of the flare, the spectra of the two main components peak just short of 1 THz. To statistically explain the observed variability of the (sub-)mm spectrum of SgrA*, we use a sample of simultaneous NIR/X-ray flare peaks and model the flares using a synchrotron and SSC mechanism. Conclusions. These parameters suggest that either the adiabatically expanding source components have a bulk motion larger than v exp or the expanding material contributes to a corona or disk, confined to the immediate surroundings of SgrA*. For the bulk of the synchrotron and SSC models, we find synchrotron turnover frequencies in the range of 300−400 GHz. For the pure synchrotron models, this results in densities of relativistic particles of the order of 10 6.5 cm −3 and for the SSC models, the median densities are about one order of magnitude higher. However, to obtain a realistic description of the frequency-dependent variability amplitude of SgrA*, models with higher turnover frequencies and even higher densities are required.

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INFLOW-OUTFLOW MODEL WITH CONDUCTION AND SELF-CONSISTENT FEEDING FOR Sgr A*

Cited by 88 publications

References 35 publications

Coupled jet-disk model for Sagittarius A*: explaining the flat-spectrum radio core with GRMHD simulations of jets

Coupled jet-disk model for Sagittarius A*: explaining the flat-spectrum radio core with GRMHD simulations of jets

THE POWER OF IMAGING: CONSTRAINING THE PLASMA PROPERTIES OF GRMHD SIMULATIONS USING EHT OBSERVATIONS OF Sgr A*

Millimeter to X-ray flares from Sagittarius A*

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