Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 497, Issue 4, Pages 4999-5007Publisher
OXFORD UNIV PRESS
DOI: 10.1093/mnras/staa2288
Keywords
accretion, accretion discs; black hole physics; MHD; polarization; radiative transfer; Galaxy: centre
Categories
Funding
- Sofja Kovalevskaja Award from the Alexander von Humboldt Foundation
- CONACYT/DAAD grant [57265507]
- NASA Astrophysics Theory Program [80NSSC20K0527]
- Gordon and Betty Moore Foundation [GBMF7392]
- National Science Foundation [NSF PHY-1748958]
- National Science Foundation AAG [1815304, 1911080]
- NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center
- Direct For Mathematical & Physical Scien
- Division Of Astronomical Sciences [1911080] Funding Source: National Science Foundation
- Direct For Mathematical & Physical Scien
- Division Of Astronomical Sciences [1815304] Funding Source: National Science Foundation
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Large-amplitude Sgr A* near-infrared (NIR) flares result from energy injection into electrons near the black hole event horizon. Astrometry data show continuous rotation of the emission region during bright flares, and corresponding rotation of the linear polarization angle. One broad class of physical flare models invokes magnetic reconnection. Here, we show that such a scenario can arise in a general relativistic magnetohydrodynamic simulation of a magnetically arrested disc. Saturation of magnetic flux triggers eruption events, where magnetically dominated plasma is expelled from near the horizon and forms a rotating, spiral structure. Dissipation occurs via reconnection at the interface of the magnetically dominated plasma and surrounding fluid. This dissipation is associated with large increases in NIR emission in models of Sgr A*, with durations and amplitudes consistent with the observed flares. Such events occur at roughly the time-scale to re-accumulate the magnetic flux from the inner accretion disc, similar or equal to 10 h for Sgr A*. We study NIR observables from one sample event to show that the emission morphology tracks the boundary of the magnetically dominated region. As the region rotates around the black hole, the NIR centroid and linear polarization angle both undergo continuous rotation, similar to the behaviour seen in Sgr A* flares.
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