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A Possible Rossby Wave Instability Origin for the Flares in Sagittarius A

Michel Tagger 1 F. Melia
1 APC-Gravitation - APC - Gravitation
APC (UMR_7164) - AstroParticule et Cosmologie, AEI - Max-Planck-Institut für Gravitationsphysik ( Albert-Einstein-Institut )
Abstract : In recent years, near-IR and X-ray flares have been detected from the Galaxy's central radio point source, Sagittarius A* (Sgr A*), believed to be a \~3.10^6 solar masses supermassive black hole. In some cases, the transient emission appears to be modulated with a (quasi-)periodic oscillation (QPO) of ~ 17-20 minutes. The implied ~ 3 r_S size of the emitter (where r_S = 2GM/c^2 is the Schwarzschild radius) points to an instability - possibly induced by accretion - near the Marginally Stable Orbit (MSO) of a slowly spinning object. But Sgr A* is not accreting via a large, 'standard' disk; instead, the low density environment surrounding it apparently feeds the black hole with low angular momentum clumps of plasma that circularize within ~ 10-300 r_S and merge onto a compact, hot disk. In this Letter, we follow the evolution of the disk following such an event, and show that a Rossby wave instability, particularly in its magnetohydrodynamic (MHD) form, grows rapidly and produces a period of enhanced accretion lasting several hours. Both the amplitude of this response, and its duration, match the observed flare characteristics rather well.
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http://hal.in2p3.fr/in2p3-00025149
Contributor : Simone Lantz <>
Submitted on : Tuesday, November 29, 2005 - 3:36:15 PM
Last modification on : Saturday, September 19, 2020 - 4:53:22 AM

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Michel Tagger, F. Melia. A Possible Rossby Wave Instability Origin for the Flares in Sagittarius A. Astrophysical Journal Letters, IOP Science, 2006, 636, pp.L33-L36. ⟨10.1086/499806⟩. ⟨in2p3-00025149⟩

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