Radiative Models of SGR A* From GRMHD Simulations

Mościbrodzka, Monika; Gammie, Charles F.; Dolence, Joshua C.; Shiokawa, Hotaka; Leung, Po Kin

doi:10.1088/0004-637x/706/1/497

Cited by 310 publications

(448 citation statements)

References 62 publications

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“…The typical values that describe the physical conditions there are number densities of n ∼ 5 × 10 7 cm 3 , magnetic fields of B ∼ 50 G, and electron temperatures of T e ∼ 5 × 10 10 K. These values are consistent with the results obtained by several other authors (e.g. Yuan et al 2003;Goldston et al 2005;Moscibrodzka et al 2009) and reflect results obtained from X-ray measurements for the central few 10 R s (Baganoff et al 2001(Baganoff et al , 2003.…”

Section: Sub-mm Variability From a Magnetized Accretion Flowsupporting

confidence: 90%

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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 Flowsupporting

confidence: 90%

“…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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“…Specifically, we have studied the impact of realistic electron heating and electron thermal conduction on the spatial distribution of the electron temperature in 2D (axisymmetric) simulations of black hole accretion onto a rotating black hole. We find that the resulting electron temperatures differ significantly from the assumption of a constant electron to proton temperature ratio used in previous work to predict the emission from GRMHD simulations (Mościbrodzka et al 2009;Dibi et al 2012;Drappeau et al 2013);see, e.g. Figures 9-11.…”

Section: Discussioncontrasting

confidence: 75%

Electron thermodynamics in GRMHD simulations of low-luminosity black hole accretion

Ressler

Tchekhovskoy

Quataert

et al. 2015

Mon. Not. R. Astron. Soc.

174

238

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Simple assumptions made regarding electron thermodynamics often limit the extent to which general relativistic magnetohydrodynamic (GRMHD) simulations can be applied to observations of low-luminosity accreting black holes. We present, implement, and test a model that self-consistently evolves an entropy equation for the electrons and takes into account the effects of spatially varying electron heating and relativistic anisotropic thermal conduction along magnetic field lines. We neglect the back-reaction of electron pressure on the dynamics of the accretion flow. Our model is appropriate for systems accreting at ≪ 10 −5 of the Eddington accretion rate, so radiative cooling by electrons can be neglected. It can be extended to higher accretion rates in the future by including electron cooling and proton-electron Coulomb collisions. We present a suite of tests showing that our method recovers the correct solution for electron heating under a range of circumstances, including strong shocks and driven turbulence. Our initial applications to axisymmetric simulations of accreting black holes show that (1) physically-motivated electron heating rates that depend on the local magnetic field strength yield electron temperature distributions significantly different from the constant electron to proton temperature ratios assumed in previous work, with higher electron temperatures concentrated in the coronal region between the disc and the jet; (2) electron thermal conduction significantly modifies the electron temperature in the inner regions of black hole accretion flows if the effective electron mean free path is larger than the local scale-height of the disc (at least for the initial conditions and magnetic field configurations we study). The methods developed in this work are important for producing more realistic predictions for the emission from accreting black holes such as Sagittarius A* and M87; these applications will be explored in future work.

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“…Sgr A * 's accretion rate is very low (Ṁ < 2 × 10 −7 M yr −1 ) as deduced from observations of polarization and Faraday rotation measurements (Bower et al 2003;Marrone et al 2007). This accretion rate is consistent with general relativistic magnetohydrodynamical (GRMHD) simulations that estimate a rate of a few times 10 −9 M yr −1 (Mościbrodzka et al 2009;Drappeau et al 2013). The bulk of the emission from Sgr A * is observed at radio and submillimeter frequencies, reaching a maximum of about 1 Jansky at the peak of the spectrum (e.g.…”

Section: Introductionsupporting

confidence: 87%

Using infrared/X-ray flare statistics to probe the emission regions near the event horizon of Sgr A*

Dibi

Markoff

Belmont

et al. 2016

Mon. Not. R. Astron. Soc.

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The supermassive black hole at the centre of the Galaxy flares at least daily in the infrared (IR) and X-ray bands, yet the process driving these flares is still unknown. So far detailed analysis has only been performed on a few bright flares. In particular, the broadband spectral modelling suffers from a strong lack of simultaneous data. However, new monitoring campaigns now provide data on thousands of flaring events, allowing a statistical analysis of the flare properties. In this paper, we investigate the X-ray and IR flux distributions of the flare events.Using a self-consistent calculation of the particle distribution, we model the statistical properties of the flares. Based on a previous work on single flares, we consider two families of models: pure synchrotron models and synchrotron self-Compton (SSC) models. We investigate the effect of fluctuations in some relevant parameters (e.g. acceleration properties, density, magnetic field) on the flux distributions. The distribution of these parameters is readily derived from the flux distributions observed at different wavelengths.In both scenarios, we find that fluctuations of the power injected in accelerated particles plays a major role. This must be distributed as a power-law (with different indices in each model). In the synchrotron dominated scenario, we derive the most extreme values of the acceleration power required to reproduce the brightest flares. In that model, the distribution of the acceleration slope fluctuations is constrained and in the SSC scenario we constrain the distributions of the correlated magnetic field and flow density variations.

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Radiative Models of SGR A* From GRMHD Simulations

Cited by 310 publications

References 62 publications

Millimeter to X-ray flares from Sagittarius A*

Millimeter to X-ray flares from Sagittarius A*

Electron thermodynamics in GRMHD simulations of low-luminosity black hole accretion

Using infrared/X-ray flare statistics to probe the emission regions near the event horizon of Sgr A*

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