The Relationship Between Simulated Sub-Millimeter and Near-Infrared Images of Sagittarius A* from a Magnetically Arrested Black Hole Accretion Flow

Abstract

Sagittarius A* (Sgr A*), the supermassive black hole at the center of the Milky Way, undergoes large-amplitude near-infrared (NIR) flares that can coincide with the continuous rotation of the NIR emission region. One promising explanation for this observed NIR behavior is a magnetic flux eruption, which occurs in three-dimensional General Relativistic Magneto-Hydrodynamic (3D GRMHD) simulations of magnetically arrested accretion flows. After running two-temperature 3D GRMHD simulations, where the electron temperature is evolved self-consistently along with the gas temperature, it is possible to calculate ray-traced images of the synchotron emission from thermal electrons in the accretion flow. Changes in the gas dominated ($\sigma =b^2/2\rho <1$) regions of the accretion flow during a magnetic flux eruption reproduce the NIR flaring and NIR emission region rotation of Sgr A* with durations consistent with observation. In this paper, we demonstrate that these models also predict that large (1.5x - 2x) size increases of the sub-millimeter (sub-mm) and millimeter (mm) emission region follow most NIR flares by 20 - 50 minutes. These size increases occur across a wide parameter space of black hole spin ($a=0.3,0.5,-0.5,0.9375$) and initial tilt angle between the accretion flow and black hole spin axes ${\theta }_0$ (${\theta }_0=0^{\circ }$, $16^{\circ }$, $30^{\circ }$). We also calculate the sub-mm polarization angle rotation and the shift of the sub-mm spectral index from zero to -0.8 during a prominent NIR flare in our high spin ($a=0.9375$) simulation. We show that, during a magnetic flux eruption, a large ($\sim 10r_g$), magnetically dominated $(\sigma >1)$, low density, and high temperature ``bubble'' forms in the accretion flow. The drop in density inside the bubble and additional electron heating in accretion flow between 15$r_g$ - 25$r_g$ leads to a sub-mm size increase in corresponding images.

arXiv comment18 pages, 15 figures. Monthly Notices of the Royal Astronomical Society, 2024

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Cited by in corpus (4)

• New Evidence for a Flux-independent Spectral Index of Sgr A* in the Near-infrared
• Non-thermal Synchrotron Emission and Polarization Signatures during Black Hole Flux Eruptions
• Radiative Cooling Effects on Plasmoid Formation in Black Hole Accretion Flows with Multiple Magnetic Loops
• Polarization Signatures of Magnetic Reconnection Bubbles near Black Holes