ALMA Observations of the Terahertz Spectrum of Sagittarius A*

Abstract

We present ALMA observations at 233, 678, and 870 GHz of the Galactic Center black hole, Sagittarius A*. These observations reveal a flat spectrum over this frequency range with spectral index $\alpha \approx -0.3$, where the flux density $S\propto {\nu }^{\alpha }$. We model the submm and far infrared spectrum with a one zone synchrotron model of thermal electrons. We infer electron densities $n=(2-5)\times 10^6$ cm${}^{-3}$, electron temperatures $T_e=(1-3)\times 10^{11}$ K, and magnetic field strength $B=10-50$ G. The parameter range can be further constrained using the observed quiescent X-ray luminosity. The flat submm spectrum results in a high electron temperature and implies that the emitting electrons are efficiently heated. We also find that the emission is most likely optically thin at 233 GHz. These results indicate that millimeter and submillimeter wavelength very long baseline interferometry of Sgr A* including those of the Event Horizon Telescope should see a transparent emission region down to event horizon scales.

Accepted for publication in ApJL

References in corpus (37)

• First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole
• First M87 Event Horizon Telescope Results. VI. The Shadow and Mass of the Central Black Hole
• First M87 Event Horizon Telescope Results. IV. Imaging the Central Supermassive Black Hole
• First M87 Event Horizon Telescope Results. V. Physical Origin of the Asymmetric Ring
• First M87 Event Horizon Telescope Results. II. Array and Instrumentation
• Detection of the gravitational redshift in the orbit of the star S2 near the Galactic centre massive black hole
• First M87 Event Horizon Telescope Results. III. Data Processing and Calibration
• Event-horizon-scale structure in the supermassive black hole candidate at the Galactic Centre
• Detection of orbital motions near the last stable circular orbit of the massive black hole SgrA*
• An Unambiguous Detection of Faraday Rotation in Sagittarius A*
• The Submillimeter Bump in Sgr A* from Relativistic MHD Simulations
• Simulating the Emission and Outflows from Accretion Disks
• Observational appearance of inefficient accretion flows and jets in 3D GRMHD simulations: Application to Sgr~A*
• The Disc-Jet Symbiosis Emerges: Modeling the Emission of Sagittarius A* with Electron Thermodynamics
• Plasma diagnostic potential of 2p4f in N${}^{+}$ -- accurate wavelengths and oscillator strengths
• The Power of Imaging: Constraining the Plasma Properties of GRMHD Simulations using EHT Observations of Sgr A*
• Thermal disequilibration of ions and electrons by collisionless plasma turbulence
• Radio and Millimeter Monitoring of Sgr A*: Spectrum, Variability, and Constraints on the G2 Encounter
• Electron and proton heating in trans-relativistic magnetic reconnection
• Variability Timescale and Spectral Index of Sgr A* in the Near Infrared: Approximate Bayesian Computation Analysis of the Variability of the Closest Supermassive Black Hole
• Results from an extensive simultaneous broadband campaign on the underluminous active nucleus M81*: further evidence for mass-scaling accretion in black holes
• The Scattering and Intrinsic Structure of Sagittarius A* at Radio Wavelengths
• Faraday rotation in GRMHD simulations of the jet launching zone of M87
• The Rotation Measure and 3.5mm Polarization of Sgr A*
• Detection of intrinsic source structure at ~3 Schwarzschild radii with Millimeter-VLBI observations of SAGITTARIUS A*
• ALMA Polarimetry of Sgr A*: Probing the Accretion Flow from the Event Horizon to the Bondi Radius
• Simulations of imaging the event horizon of Sagittarius A* from space
• Simultaneous NIR/sub-mm observation of flare emission from SgrA*
• ALMA and VLA measurements of frequency-dependent time lags in Sagittarius A*: evidence for a relativistic outflow
• The X-ray Flux Distribution of Sagittarius A* as Seen by Chandra
• The Intrinsic Two-Dimensional Size of Sagittarius A*
• The impact of Faraday effects on polarized black hole images of Sagittarius A*
• Propagation Effects in Magnetized Transrelativistic Plasmas
• Disentangling the Circumnuclear Environs of Centaurus A: III. An Inner Molecular Ring, Nuclear Shocks and the CO to warm H2 interface
• A Detection of Sgr A* in the far infrared
• The millimeter-wave continuum spectrum of Centaurus A and its nucleus
• A jet-dominated model for a broad-band spectral energy distribution of the nearby low-luminosity active galactic nucleus in M94

Cited by in corpus (37)

• First Sagittarius A* Event Horizon Telescope Results. VI: Testing the Black Hole Metric
• First Sagittarius A* Event Horizon Telescope Results. V. Testing Astrophysical Models of the Galactic Center Black Hole
• First Sagittarius A* Event Horizon Telescope Results. III: Imaging of the Galactic Center Supermassive Black Hole
• First Sagittarius A* Event Horizon Telescope Results. II. EHT and Multi-wavelength Observations, Data Processing, and Calibration
• Event Horizon Telescope observations of the jet launching and collimation in Centaurus A
• Millimeter light curves of Sagittarius A* observed during the 2017 Event Horizon Telescope campaign
• Rapid Variability of Sgr A* across the Electromagnetic Spectrum
• A parameter survey of Sgr A* radiative models from GRMHD simulations with self-consistent electron heating
• Sgr A* X-ray flares from non-thermal particle acceleration in a magnetically arrested disc
• Constraining particle acceleration in Sgr A* with simultaneous GRAVITY, Spitzer, NuSTAR and Chandra observations
• The Flux Distribution of Sgr A*
• General relativistic MHD simulations of non-thermal flaring in Sagittarius A*
• Spectral and Imaging properties of Sgr A* from High-Resolution 3D GRMHD Simulations with Radiative Cooling
• Polarimetric signatures of hot spots in black hole accretion flows
• Reconnection-driven flares in 3D black hole magnetospheres -- A scenario for hot spots around Sagittarius A*
• Magnetic reconnection plasmoid model for Sagittarius A* flares
• Using Machine Learning to Link Black Hole Accretion Flows with Spatially Resolved Polarimetric Observables
• Time Variations in the Flux Density of Sgr A* at 230 GHz Detected with ALMA
• Probing spacetime and accretion model for the Galactic Center: Comparison of Kerr and dilaton black hole shadows
• The intrinsic structure of Sagittarius A* at 1.3 cm and 7 mm
• Persistent Non-Gaussian Structure in the Image of Sagittarius A* at 86 GHz
• Second Scale Submillimeter Variability of Sagittarius A* during flaring activity of 2019: On the Origin of Bright Near Infrared Flares
• The Effects of Gas Angular Momentum on the Formation of Magnetically Arrested Disks and the Launching of Powerful Jets
• General relativistic effects and the near-infrared and X-ray variability of Sgr A* I
• Multi-wavelength Variability of Sagittarius A* in July 2019
• Electromagnetic Emission from a Binary Black Hole Merger Remnant in Plasma: Field Alignment and Plasma Temperature
• How Spatially Resolved Polarimetry Informs Black Hole Accretion Flow Models
• Probing Plasma Physics with Spectral Index Maps of Accreting Black Holes on Event Horizon Scales
• Magnetic field structure in the vicinity of a super-massive black hole in low luminosity galaxies: the case of Sgr A*
• The Chandra High Resolution X-ray Spectrum of Quiescent Emission from Sgr A*
• Magnetic flux eruptions at the root of time-lags in low-luminosity AGN
• Observational Constraints on Direct Electron Heating in the Hot Accretion Flows in Sgr A* and M87*
• New Evidence for a Flux-independent Spectral Index of Sgr A* in the Near-infrared
• Scale-invariance of black hole accretion: modeling emission from a black hole X-ray binary with relativistic accretion flow simulations
• The X-ray variation of M81* resolved by Chandra and NuSTAR
• HOLESOM: Constraining the Properties of Slowly-Accreting Massive Black Holes with Self-Organizing Maps
• Radiative energy from a reconnection region around massive black hole