Detection of intrinsic source structure at ~3 Schwarzschild radii with Millimeter-VLBI observations of SAGITTARIUS A*

Abstract

We report results from very long baseline interferometric (VLBI) observations of the supermassive black hole in the Galactic center, Sgr A*, at 1.3 mm (230 GHz). The observations were performed in 2013 March using six VLBI stations in Hawaii, California, Arizona, and Chile. Compared to earlier observations, the addition of the APEX telescope in Chile almost doubles the longest baseline length in the array, provides additional {\it uv} coverage in the N-S direction, and leads to a spatial resolution of $\sim$30 $\mu$as ($\sim$3 Schwarzschild radii) for Sgr A*. The source is detected even at the longest baselines with visibility amplitudes of $\sim$4-13% of the total flux density. We argue that such flux densities cannot result from interstellar refractive scattering alone, but indicate the presence of compact intrinsic source structure on scales of $\sim$3 Schwarzschild radii. The measured nonzero closure phases rule out point-symmetric emission. We discuss our results in the context of simple geometric models that capture the basic characteristics and brightness distributions of disk- and jet-dominated models and show that both can reproduce the observed data. Common to these models are the brightness asymmetry, the orientation, and characteristic sizes, which are comparable to the expected size of the black hole shadow. Future 1.3 mm VLBI observations with an expanded array and better sensitivity will allow a more detailed imaging of the horizon-scale structure and bear the potential for a deep insight into the physical processes at the black hole boundary.

arXiv comment11 pages, 5 figures, accepted to ApJ

References in corpus (43)

• Exchange Monte Carlo Method and Application to Spin Glass Simulations
• The Galactic Center Massive Black Hole and Nuclear Star Cluster
• Viewing the Shadow of the Black Hole at the Galactic Center
• Information criteria for astrophysical model selection
• Event-horizon-scale structure in the supermassive black hole candidate at the Galactic Centre
• DiFX2: A more flexible, efficient, robust and powerful software correlator
• GRMHD Simulations of Magnetized Advection Dominated Accretion on a Non-Spinning Black Hole: Role of Outflows
• The Supermassive Black Hole at the Galactic Center
• Jet Launching Structure Resolved Near the Supermassive Black Hole in M87
• Stability of Relativistic Jets from Rotating, Accreting Black Holes via Fully Three-Dimensional Magnetohydrodynamic Simulations
• Radiative Models of Sgr A* from GRMHD Simulations
• An Improved Distance and Mass Estimate for Sgr A* from a Multistar Orbit Analysis
• A size of ~1 AU for the radio source Sgr A* at the centre of the Milky Way
• Imaging Optically-Thin Hot Spots Near the Black Hole Horizon of Sgr A* at Radio and Near-Infrared Wavelengths
• The Submillimeter Bump in Sgr A* from Relativistic MHD Simulations
• Resolved Magnetic-Field Structure and Variability Near the Event Horizon of Sagittarius A*
• 1.3 mm Wavelength VLBI of Sagittarius A*: Detection of Time-Variable Emission on Event Horizon Scales
• Detection of the Intrinsic Size of Sagittarius A* through Closure Amplitude Imaging (includes Online Supporting Material)
• The Intrinsic Size of Sagittarius A* from 0.35 cm to 6 cm
• Observational appearance of inefficient accretion flows and jets in 3D GRMHD simulations: Application to Sgr~A*
• The Power of Imaging: Constraining the Plasma Properties of GRMHD Simulations using EHT Observations of Sgr A*
• Plasma diagnostic potential of 2p4f in N${}^{+}$ -- accurate wavelengths and oscillator strengths
• Estimating the Parameters of Sgr A*'s Accretion Flow Via Millimeter VLBI
• Towards the event horizon -- the supermassive black hole in the Galactic Center
• Coupled jet-disk model for Sgr A*: explaining the flat-spectrum radio core with GRMHD simulations of jets
• Millimeter Flares and VLBI Visibilities from Relativistic Simulations of Magnetized Accretion onto the Galactic Center Black Hole
• 230 GHz VLBI observations of M87: event-horizon-scale structure at the enhanced very-high-energy $\gamma$-ray state in 2012
• Tilted black hole accretion disc models of Sagittarius A*: time-variable millimetre to near-infrared emission
• Theory and Simulations of Refractive Substructure in Resolved Scatter-Broadened Images
• Persistent Asymmetric Structure of Sagittarius A* on Event Horizon Scales
• Imaging an Event Horizon: Mitigation of Scattering Toward Sagittarius A*
• The Proper Motion of the Galactic Center Pulsar Relative to Sagittarius A*
• A geometric crescent model for black hole images
• The Intrinsic Two-Dimensional Size of Sagittarius A*
• Discovery of Substructure in the Scatter-Broadened Image of Sgr A*
• Imaging an Event Horizon: Mitigation of Source Variability of Sagittarius A*
• Stochastic Optics: A Scattering Mitigation Framework for Radio Interferometric Imaging
• Fine-scale structure of the quasar 3C 279 Measured with 1.3 mm very long baseline interferometry
• The Optics of Refractive Substructure
• Bayesian techniques for comparing time-dependent GRMHD simulations to variable Event Horizon Telescope observations
• Wisps in the Galactic center: NIR triggered observations of the radio source Sgr A* at 43 GHz
• First 230 GHz VLBI Fringes on 3C 279 using the APEX Telescope
• Resolving the inner jet structure of 1924-292 with the EVENT HORIZON TELESCOPE

Cited by in corpus (54)

• First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole
• First Sagittarius A* Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole in the Center of the Milky Way
• First M87 Event Horizon Telescope Results. II. Array and Instrumentation
• First M87 Event Horizon Telescope Results. III. Data Processing and Calibration
• 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
• The Event Horizon General Relativistic Magnetohydrodynamic Code Comparison Project
• On the charge of the Galactic centre black hole
• The role of electron heating physics in images and variability of the Galactic Centre black hole Sagittarius A*
• The Size, Shape, and Scattering of Sagittarius A* at 86 GHz: First VLBI with ALMA
• Polarimetric properties of Event Horizon Telescope targets from ALMA
• The Scattering and Intrinsic Structure of Sagittarius A* at Radio Wavelengths
• Faraday rotation in the jet of M87 inside the Bondi radius: indication of winds from hot accretion flows confining the relativistic jet
• Shadow of a black hole at cosmological distance
• Extended Uncertainty Principle Black Holes
• 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
• A parameter survey of Sgr A* radiative models from GRMHD simulations with self-consistent electron heating
• Scalar field effects on the orbit of S2 star
• Rapid Variability of Sgr A* across the Electromagnetic Spectrum
• Black hole shadow as a standard ruler in cosmology
• Monitoring the Morphology of M87* in 2009-2017 with the Event Horizon Telescope
• Constraining the charge of the Galactic centre black hole
• Constraints on a tidal charge of the supermassive black hole in M87* with the EHT observations in April 2017
• ALMA Observations of the Terahertz Spectrum of Sagittarius A*
• EHT-HOPS pipeline for millimeter VLBI data reduction
• Metrics and Motivations for Earth-Space VLBI: Time-Resolving Sgr A* with the Event Horizon Telescope
• Effect of Electromagnetic Interaction on Galactic Center Flare Components
• Spatially resolved origin of mm-wave linear polarization in the nuclear region of 3C 84
• Simulations of M87 and Sgr A* Imaging with the Millimetron Space Observatory on near-Earth orbits
• Testing the ALP-photon coupling with polarization measurements of Sagittarius A*
• On the Comparison of AGN with GRMHD Simulations: I. Sgr A*
• The Galactic Center as a laboratory for theories of gravity and dark matter
• Visibility of Black Hole Shadows in Low-luminosity AGN
• Positron Effects on Polarized Images and Spectra from Jet and Accretion Flow Models of M87* and Sgr A*
• Black hole Spin Measurement Based on Time-domain VLBI Observations of Infalling Gas Cloud
• 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
• An 86-GHz search for Pulsars in the Galactic Center with the Atacama Large Millimeter/submillimeter Array
• General relativistic effects and the near-infrared and X-ray variability of Sgr A* I
• Constrains on the electric charges of the binary black holes with GWTC-1 events
• VLBI imaging of black holes via second moment regularization
• Micro-arcsecond structure of Sagittarius A* revealed by high-sensitivity 86 GHz VLBI observations
• Resolving the Nuclear Radio Emission from M32 with Very Large Array
• Imaging the event horizon of M87* from space on different timescales
• Possible evidence from the flaring activity of Sgr A* for a star at a distance of ~3.3 Schwarzscild radii from the blackhole
• Probing Accretion Turbulence in the Galactic Center with EHT Polarimetry
• A proof-of-concept neural network for inferring parameters of a black hole from partial interferometric images of its shadow
• Prospects for Wideband VLBI Correlation in the Cloud
• Seeing relativity -- II. Revisiting and visualizing the Reissner-Nordström metric
• Detecting Black Hole Occultations by Stars with Space Interferometric Telescopes
• Effects of non-vanishing dark matter pressure in the Milky Way galaxy
• The Core-shift of Sagittarius A* as a Discriminant between Disk and Jet Emission Models with millimeter-VLBI
• Shadow cast by a rotating black hole with anisotropic matter