Properties of the Radio-Emitting Gas Around SgrA*

Abstract

We show that the radial profiles of the temperature and density of the electrons as well as the magnetic field strength around the massive black hole at the Galactic center, SgrA*, may be constrained directly from existing radio data without any need to make prior assumptions about the dynamics of the emitting gas. The observed spectrum and wavelength-dependent angular size of SgrA* indicate that the synchrotron emission originates from an optically-thick plasma of quasi-thermal electrons. We find that the electron temperature rises above the virial temperature within tens of Schwarzschild radii from the black hole, suggesting that the emitting plasma may be outflowing. Constraints on the electron density profile are derived from polarization measurements. Our best-fit results differ from expectations based on existing theoretical models. However, these models cannot be ruled out as of yet due to uncertainties in the source size measurements. Our constraints could tighten considerably with future improvements in the size determination and simultaneous polarization measurements at multiple wavelengths.

6 pages, 1 figure, accepted for publication in JCAP (Journal of Cosmology & Astroparticle Physics)

References in corpus (8)

• An Unambiguous Detection of Faraday Rotation in Sagittarius A*
• The Intrinsic Size of Sagittarius A* from 0.35 cm to 6 cm
• The Rotation Measure and 3.5mm Polarization of Sgr A*
• Hot Accretion With Conduction: Spontaneous Thermal Outflows
• Sub-milliarcsecond Imaging of SgrA* and M87
• Testing RIAF model for Sgr A* using the size measurements
• Testing General Relativity with High-Resolution Imaging of Sgr A*
• Accretion models of Sgr A*

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• Simultaneous Chandra, CSO and VLA Observations of Sgr A*: The Nature of Flaring Activity
• Magnetization degree at the jet base of M87 derived from the event horizon telescope data: Testing magnetically driven jet paradigm
• Constraining particle acceleration in Sgr A* with simultaneous GRAVITY, Spitzer, NuSTAR and Chandra observations
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• The origin of hotspots around Sgr A*: Orbital or pattern motion?
• Faraday Rotation in Global Accretion Disk Simulations: Implications for Sgr A*
• Accretion of Low Angular Momentum Material onto Black Holes: Radiation Properties of Axisymmetric MHD Flows
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• Constraining Radiatively Inefficient Accretion Flows with Polarization
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• Measuring the Direction and Angular Velocity of a Black Hole Accretion Disk via Lagged Interferometric Covariance
• Long-term monitoring of Sgr A* at 7 mm with VERA and KaVA