New Constraints on the Nature of Radio Emission in Sagittarius A*

Abstract

The mm to sub-mm spectrum of Sgr A* at the Galactic center, as well as its polarization characteristics, are consistent with the inner 10 Schwarzschild radii of a tight Keplerian emitting region of hot, magnetized, orbiting gas. This plasma may also be the source through self-Comptonization of the X-rays detected by Chandra. It has long been suspected that the circularization region between the quasi-spherical infall at large radii, and this inner zone, is responsible for producing the rest of Sgr A*'s spectrum. In this paper, we report the results of a detailed study of this region. First, the combination of existing cm and X-ray data preclude the possibility of producing the observed strong 1.36 GHz radio flux via thermal synchrotron within a bounded flow. If Sgr A*'s radio spectrum is produced by accreting gas, it appears that a non-thermal particle distribution is a necessity. Second, if this is the correct picture for how Sgr A*'s spectrum is produced, it appears that the Chandra-detected X-rays may originate either from self-Comptonization in the inner Keplerian region, or from optically-thin nonthermal synchrotron emission in the much larger, circularization zone, extending up to 500 Schwarzschild radii or more. This is a question that should be answered by upcoming broadband observations, since the mm-bump and X-rays are strongly correlated in the former case, whereas the X-rays are strongly correlated to the cm-radio flux in the latter. In addition, X-rays produced in the circularized gas could show periodic or quasi-periodic variations, but not those produced via nonthermal synchrotron emission much farther out.

arXiv comment15 pages, 2 figures, ApJ Letters, In press

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• Interferometric Detection of Linear Polarization from Sagittarius A* at 230 GHz
• On The Nature of the Variable Infrared Emission from Sgr A*
• Flaring Activity of Sgr A* at 43 and 22 GHz: Evidence for Expanding Hot Plasma
• A Multi-Wavelength Study of Sgr A*: The Role of Near-IR Flares in Production of X-ray, Soft $\gamma$-ray and Sub-millimeter Emission
• Simultaneous Chandra, CSO and VLA Observations of Sgr A*: The Nature of Flaring Activity
• Simultaneous Multi-Wavelength Observations of Sgr A* during 2007 April 1-11
• Results from an extensive simultaneous broadband campaign on the underluminous active nucleus M81*: further evidence for mass-scaling accretion in black holes
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• Variable Linear Polarization from Sagittarius A*: Evidence for a Hot Turbulent Accretion Flow
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• Stochastic Electron Acceleration During the NIR and X-ray Flares in Sagittarius A*
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• Spin-Induced Disk Precession in the Supermassive Black Hole at the Galactic Center
• General relativistic MHD simulations of non-thermal flaring in Sagittarius A*
• MHD Simulations of Accretion onto Sgr A*: Quiescent Fluctuations, Outbursts, and Quasi-Periodicity
• A comparison of the R_h=ct and LCDM cosmologies using the Cosmic Distance Duality Relation
• ATCA Survey of Ammonia in the Galactic Center: The Temperatures of Dense Gas Clumps between SgrA* and SgrB2
• X-ray and Radio Variability of M31*, The Andromeda Galaxy Nuclear Supermassive Black Hole
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• Covariant Kinetic Theory with an Application to the Coma Cluster
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• MC Simulations of the Broadband Spectra of Sagittarius A* through the use of GRMHD
• A Numerical Assessment of Cosmic-ray Energy Diffusion through Turbulent Media
• The Nature of Linearly Polarized Millimeter and Sub-millimeter Emission in Sagittarius A*
• Diffusive Cosmic-ray Acceleration in Sagittarius A*
• Monitoring the Galactic Centre with Australia Telescope Compact Array
• Spin-Induced Disk Precession in Sagittarius A*
• Unseen Progenitors of Luminous High-z Quasars in the R_h=ct Universe
• Long-Term Radio Modulation in Sagittarius A* from Spin-Induced Disk Precession
• A Relativistic Disk in Sagittarius A*
• Polarimetric Imaging of Sgr A* in its Flaring State