Monte Carlo simulations of the broad-band spectra of Sagittarius A* through the use of general relativistic magnetohydrodynamics

Hilburn, Guy; Liang, Edison; Liu, Siming; Li, Hui

doi:10.1111/j.1365-2966.2009.15787.x

Cited by 15 publications

(17 citation statements)

References 36 publications

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“…Sgr A* has already been modelled in several numerical studies (e.g. Goldston, Quataert & Igumenshchev ; Ohsuga, Kato & Mineshige ; Dexter, Agol & Fragile ; Mościbrodzka et al ; Dexter et al ; Hilburn et al ; Shcherbakov, Penna & McKinney ; Dexter & Fragile ; Dolence et al ; Shiokawa et al ). All of these models consist of two separate codes: a GRMHD code describing the dynamics, and then a subsequent code to calculate the radiative emission based on the output of the first one.…”

Section: Introductionmentioning

confidence: 99%

General relativistic magnetohydrodynamic simulations of accretion on to Sgr A*: how important are radiative losses?

Dibi

Drappeau

Fragile

et al. 2012

Monthly Notices of the Royal Astronomical Society

103

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We present general relativistic magnetohydrodynamic numerical simulations of the accretion flow around the supermassive black hole in the Galactic Centre, Sagittarius A* (Sgr A*). The simulations include for the first time radiative cooling processes (synchrotron, bremsstrahlung and inverse Compton) self‐consistently in the dynamics, allowing us to test the common simplification of ignoring all cooling losses in the modelling of Sgr A*. We confirm that for Sgr A*, neglecting the cooling losses is a reasonable approximation if the Galactic Centre is accreting below ∼10−8 M⊙ yr−1, i.e. Ṁ<10−7trueṀ Edd . However, above this limit, we show that radiative losses should be taken into account as significant differences appear in the dynamics and the resulting spectra when comparing simulations with and without cooling. This limit implies that most nearby low‐luminosity active galactic nuclei are in the regime where cooling should be taken into account. We further make a parameter study of axisymmetric gas accretion around the supermassive black hole at the Galactic Centre. This approach allows us to investigate the physics of gas accretion in general, while confronting our results with the well‐studied and observed source, Sgr A*, as a test case. We confirm that the nature of the accretion flow and outflow is strongly dependent on the initial geometry of the magnetic field. For example, we find it difficult, even with very high spins, to generate powerful outflows from discs threaded with multiple, separate poloidal field loops.

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Section: Introductionmentioning

confidence: 99%

General relativistic magnetohydrodynamic simulations of accretion on to Sgr A*: how important are radiative losses?

Dibi

Drappeau

Fragile

et al. 2012

Monthly Notices of the Royal Astronomical Society

103

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“…This suggests changes in accretion rate, from the average fit, of about 20%-25%. As discussed previously in Hilburn et al (2010), mass accretion rates vary in HARM trials by about a factor of two. Similarly, Dexter et al (2009Dexter et al ( , 2010 suggest variability up to about 50% for both 2D and 3D Sagittarius A* models.…”

Section: Model Tests and Evaluationmentioning

confidence: 63%

“…Evaluating HARM output to supply input data to the radiation transport code requires several steps, as described in Hilburn et al (2010).…”

Section: Modelingmentioning

confidence: 99%

Numerical Modeling of Multi-Wavelength Spectra of M87 Core Emission

Hilburn¹,

Liang²

2012

ApJ

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Spectral fits to M87 core data from radio to hard X-ray are generated via a specially selected software suite, comprised of the High-Accuracy Relativistic Magnetohydrodynamics GRMHD accretion disk model and a twodimensional Monte Carlo radiation transport code. By determining appropriate parameter changes necessary to fit X-ray-quiescent and flaring behavior of M87's core, we assess the reasonableness of various flaring mechanisms. This shows that an accretion disk model of M87's core out to 28 GM/c 2 can describe the inner emissions. High spin rates show GRMHD-driven polar outflow generation, without citing an external jet model. Our results favor accretion rate changes as the dominant mechanism of X-ray flux and index changes, with variations in density of approximately 20% necessary to scale between the average X-ray spectrum and flaring or quiescent spectra. The best-fit parameters are black hole spin a/M > 0.8 and maximum accretion flow density n 3 × 10 7 cm −3 , equivalent to horizon accretion rates betweenṁ =Ṁ/Ṁ Edd ≈ 2 × 10 −6 and 1 × 10 −5 (withṀ Edd defined assuming a radiative efficiency η = 0.1). These results demonstrate that the immediate surroundings of M87's core are appropriate to explain observed X-ray variability.

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“…Simulations based on the equilibrium torus solutions of Fishbone & Moncrief (1976) and Chakrabarti (1985) have found many applications: thin disk models (Shafee et al 2008;Noble et al 2009;Penna et al 2010) black hole spin evolution (Gammie et al 2004), radio emission from Sgr A* (Noble et al 2007;Dibi et al 2012;Shcherbakov et al 2012), black hole jets (McKinney 2006(McKinney , 2005Nagataki 2009;Tchekhovskoy et al 2011;, computations of spectra (Hilburn et al 2010), magnetized accretion with neutrino losses (Barkov & Baushev 2011;Shibata et al 2007;Barkov 2008), pair production in low luminosity galactic nuclei (Mościbrodzka et al 2011), numerical convergence studies (Shiokawa et al 2012), tilted disk evolution (Fragile et al 2007;Fragile & Blaes 2008;Henisey et al 2012), binary black hole mergers (Farris et al 2011(Farris et al , 2012, and magnetically arrested disks (De Villiers et al 2003;McKinney et al 2012).…”

Section: Introductionmentioning

confidence: 99%

A new equilibrium torus solution and GRMHD initial conditions

Penna

Kulkarni

Narayan

2013

A&A

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Context. General relativistic magnetohydrodynamic (GRMHD) simulations are providing influential models for black hole spin measurements, gamma ray bursts, and supermassive black hole feedback. Many of these simulations use the same initial condition: a rotating torus of fluid in hydrostatic equilibrium. A persistent concern is that simulation results sometimes depend on arbitrary features of the initial torus. For example, the Bernoulli parameter (which is related to outflows), appears to be controlled by the Bernoulli parameter of the initial torus. Aims. In this paper, we give a new equilibrium torus solution and describe two applications for the future. First, it can be used as a more physical initial condition for GRMHD simulations than earlier torus solutions. Second, it can be used in conjunction with earlier torus solutions to isolate the simulation results that depend on initial conditions. Methods. We assume axisymmetry, an ideal gas equation of state, constant entropy, and ignore self-gravity. We fix an angular momentum distribution and solve the relativistic Euler equations in the Kerr metric. Results. The Bernoulli parameter, rotation rate, and geometrical thickness of the torus can be adjusted independently. Our torus tends to be more bound and have a larger radial extent than earlier torus solutions. Conclusions. While this paper was in preparation, several GRMHD simulations appeared based on our equilibrium torus. We believe it will continue to provide a more realistic starting point for future simulations.

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Monte Carlo simulations of the broad-band spectra of Sagittarius A* through the use of general relativistic magnetohydrodynamics

Cited by 15 publications

References 36 publications

General relativistic magnetohydrodynamic simulations of accretion on to Sgr A*: how important are radiative losses?

General relativistic magnetohydrodynamic simulations of accretion on to Sgr A*: how important are radiative losses?

Numerical Modeling of Multi-Wavelength Spectra of M87 Core Emission

A new equilibrium torus solution and GRMHD initial conditions

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