Near-Infrared and X-ray Quasi-Periodic Oscillations in Numerical Models   of Sgr A*
  We report transient quasi-periodic oscillations (QPOs) on minute timescales in relativistic, radiative models of the galactic center source Sgr A*. The QPOs result from nonaxisymmetric $m=1$ structure in the accretion flow excited by MHD turbulence. Near-infrared (NIR) and X-ray power spectra show significant peaks at frequencies comparable to the orbital frequency at the innermost stable circular orbit (ISCO) $f_o$. The excess power is associated with inward propagating magnetic filaments inside the ISCO. The amplitudes of the QPOs are sensitive to the electron distribution function. We argue that transient QPOs appear at a range of frequencies in the neighborhood of $f_o$ and that the power spectra, averaged over long times, likely show a broad bump near $f_o$ rather than distinct, narrow QPO features. 
Joshua C. Dolence, Charles F. Gammie, Hotaka Shiokawa, Scott C. Noble
astro-ph.HE astro-ph.GA gr-qc