Millimeter Flares and Vlbi Visibilities From Relativistic Simulations of Magnetized Accretion Onto the Galactic Center Black Hole

Dexter, Jason; Agol, Eric; Fragile, P. Chris

doi:10.1088/0004-637x/703/2/l142

Cited by 128 publications

(154 citation statements)

References 38 publications

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“…Hence, these models are consistent with the observed millimeter variability of SgrA*. However, since Dexter et al (2009Dexter et al ( , 2010) concentrate only on modeling the (sub-)millimeter emission, their modeling could not reproduce the observed NIR/X-ray flares and corresponding (sub-)millimeter flares (Eckart et al 2008;Marrone et al 2008;Dodds-Eden et al 2009;Yusef-Zadeh et al 2008, which are most likely physically associated. The authors also clearly state that -in the framework of their modeling -it is unclear how their description of variability is linked to the NIR/X-ray flare activity.…”

Section: Sub-mm Variability From a Magnetized Accretion Flowmentioning

confidence: 69%

“…Observations and simulations consistently indicate that at frequencies above 200 GHz the variability amplitudes are of the order of 40%−50% (Garcia-Marin et al 2011a,b;Dexter et al 2009Dexter et al , 2010Li et al 2009;Marrone et al 2006aMarrone et al ,b, 2007. At lower frequencies (corresponding to wavelengths of 0.7 cm to 3.0 cm), the observed variability amplitudes are of the order of 10% (Macquart & Bower 2006;Bower et al 2002;Falcke et al 1998) or lower.…”

Section: Limits To the Degree Of Variabilitymentioning

confidence: 95%

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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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Section: Sub-mm Variability From a Magnetized Accretion Flowmentioning

confidence: 69%

Section: Limits To the Degree Of Variabilitymentioning

confidence: 95%

Millimeter to X-ray flares from Sagittarius A*

Eckart

García-Marín

Vogel

et al. 2012

A&A

146

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“…The images from our simulations, however, have significant asymmetry, either because they are dominated by emission in the funnel or because of Doppler effects in the disk. In principle, in order to compare our simulations to the observed image size, we will need to calculate the predicted scattering broadened visibilities in the u−v plane and compare them directly to the data (as is done, e.g., in Broderick et al 2011a andin Dexter et al 2009). However, this introduces additional free parameters in the model, such as the orientation of the black-hole spin vector on the plane of the sky, and the current coverage of the u−v plane is too sparse to allow us to constrain the model parameters significantly better than the simple estimate of the size (see, e.g., the large areas within the confidence contours in Broderick et al 2011a andin Dexter et al 2009).…”

Section: Current Spectral and Imagingmentioning

confidence: 99%

“…Finally, owing to our use of a very fast radiative transport algorithm, instead of calculating the time-averaged properties of the simulated flows before constructing images and spectra like in many previous studies, we are able to calculate images and spectra for each snapshot of the flow, before averaging them together. This approach was also taken by Dexter et al (2009Dexter et al ( , 2010 and Dexter & Fragile (2013). Albeit computationally very expensive, it mimics more closely the averaging that will inevitably occur during the EHT observations and produces results that differ considerably from the alternate procedure.…”

Section: Introductionmentioning

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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“…Noble et al 2007;Mościbrodzka et al 2009;Dexter et al 2009Dexter et al , 2010. More recent models have even included polarization measurements (Shcherbakov et al 2012).…”

Section: Matching Simulations With Observationsmentioning

confidence: 99%

Current Status of Simulations

Fragile

2013

Space Sci Rev

Self Cite

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As the title suggests, the purpose of this chapter is to review the current status of numerical simulations of black hole accretion disks. This chapter focuses exclusively on global simulations of the accretion process within a few tens of gravitational radii of the black hole. Most of the simulations discussed are performed using general relativistic magnetohydrodynamic (MHD) schemes, although some mention is made of Newtonian radiation MHD simulations and smoothed particle hydrodynamics. The goal is to convey some of the exciting work that has been going on in the past few years and provide some speculation on future directions.

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Millimeter Flares and Vlbi Visibilities From Relativistic Simulations of Magnetized Accretion Onto the Galactic Center Black Hole

Cited by 128 publications

References 38 publications

Millimeter to X-ray flares from Sagittarius A*

Millimeter to X-ray flares from Sagittarius A*

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

Current Status of Simulations

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