Astronomy and Astrophysics – Astrophysics
Scientific paper
2006-11-08
Astrophys.J.701:521-534,2009
Astronomy and Astrophysics
Astrophysics
13 pages including 12 figures, submitted to ApJ, comments welcome
Scientific paper
10.1088/0004-637X/701/1/521
High resolution observations of Sgr A* have revealed a wide variety of phenomena, ranging from intense rapid flares to quasi-periodic oscillations, making this object an ideal system to study the properties of low luminosity accreting black holes. In this paper, we use a pseudo-spectral algorithm to construct and evolve a three-dimensional magnetohydrodynamic model of the accretion disk in Sgr A*. Assuming a hybrid thermal-nonthermal emission scheme, we show that the MHD turbulence can by itself only produce factor of two fluctuations in luminosity. These amplitudes in variation cannot explain the magnitude of flares observed in this system. However, we also demonstrate that density perturbations in the disk do produce outbursts qualitatively similar to those observed by XMM-Newton in X-rays and ground-based facilities in the near infrared. Quasi-periodic oscillations emerge naturally in the simulated lightcurves. We attribute these to non-axisymmetric density perturbations that emerge as the disk evolves back toward its quiescent state.
Chan Chi-kwan
Fryer Christopher L.
Liu Siming
Melia Fulvio
Ozel Feryal
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