MHD SIMULATIONS OF ACCRETION ONTO Sgr A*: QUIESCENT FLUCTUATIONS, OUTBURSTS, AND QUASIPERIODICITY

Journal Article · Mon Aug 10 00:00:00 EDT 2009 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/701/1/521; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)· OSTI ID:21313660

Chikwan, Chan ^[1]; Siming, Liu ^[2]; Fryer, Christopher L; Psaltis, Dimitrios; Oezel, Feryal; Melia, Fulvio ^[3]; Rockefeller, Gabriel ^[4]

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1. Institute for Theory and Computation, Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)
2. Department of Physics and Astronomy, University of Glasgow, Kelvin Bldg Rm 620, Glasgow G12 8QQ (United Kingdom)
3. Department of Physics, the University of Arizona, Tucson, AZ 85721 (United States)
4. Computational Computer Science Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)

High-resolution observations of Sgr A* have revealed a wide variety of phenomena, ranging from intense rapid flares to quasi-periodic oscillations (QPOs), making this object an ideal system to study the properties of low luminosity accreting black holes. In this paper, we use a pseudospectral algorithm to construct and evolve a three-dimensional magnetohydrodynamic (MHD) model of the accretion disk in Sgr A*. Assuming a hybrid thermal-nonthermal emission scheme and calibrating the parameters by observations, we show that the MHD turbulence in the environment of Sgr A* can by itself only produce factor two fluctuations in luminosity. These fluctuations cannot explain the magnitude of flares observed in this system. However, we also demonstrate that external forcing of the accretion disk, which may be generated by the 'clumpy material' raining down onto the disk from the large-scale flow, do produce outbursts qualitatively similar to those observed by XMM-Newton in X-rays and by ground-based facilities in the near infrared. Strong, but short-term QPOs emerge naturally in the simulated light curves. We attribute these to nonaxisymmetric density perturbations that emerge as the disk evolves back toward its quiescent state.

• OSTI ID: 21313660
• Journal Information: Astrophysical Journal, Vol. 701, Issue 1; Other Information: DOI: 10.1088/0004-637X/701/1/521; Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ACCRETION DISKS
ALGORITHMS
BLACK HOLES
DISTURBANCES
FLUCTUATIONS
GALAXIES
LUMINOSITY
MAGNETOHYDRODYNAMICS
OSCILLATIONS
PERIODICITY
PERTURBATION THEORY
SIMULATION
THREE-DIMENSIONAL CALCULATIONS
TURBULENCE
X RADIATION