The Intrinsic Shape of Sagittarius A* at 3.5-mm Wavelength

Abstract

The radio emission from Sgr A${}^{\ast }$ is thought to be powered by accretion onto a supermassive black hole of $\sim 4\times 10^6{\mathrm{M}}_{\odot }$ at the Galactic Center. At millimeter wavelengths, Very Long Baseline Interferometry (VLBI) observations can directly resolve the bright innermost accretion region of Sgr A${}^{\ast }$. Motivated by the addition of many sensitive, long baselines in the north-south direction, we developed a full VLBI capability at the Large Millimeter Telescope Alfonso Serrano (LMT). We successfully detected Sgr A${}^{\ast }$ at 3.5~mm with an array consisting of 6 Very Long Baseline Array telescopes and the LMT. We model the source as an elliptical Gaussian brightness distribution and estimate the scattered size and orientation of the source from closure amplitude and self-calibration analysis, obtaining consistent results between methods and epochs. We then use the known scattering kernel to determine the intrinsic two dimensional source size at 3.5 mm: $(147\pm 7\mu \mathrm{as})\times (120\pm 12\mu \mathrm{as})$, at position angle $88^{\circ }\pm 7^{\circ }$ east of north. Finally, we detect non-zero closure phases on some baseline triangles, but we show that these are consistent with being introduced by refractive scattering in the interstellar medium and do not require intrinsic source asymmetry to explain.

10 pages, 8 figures, accepted for publication in ApJ

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• First Sagittarius A* Event Horizon Telescope Results. III: Imaging of the Galactic Center Supermassive Black Hole
• BlackHoleCam: fundamental physics of the Galactic center
• The Size, Shape, and Scattering of Sagittarius A* at 86 GHz: First VLBI with ALMA
• The Scattering and Intrinsic Structure of Sagittarius A* at Radio Wavelengths
• ALMA Polarimetry of Sgr A*: Probing the Accretion Flow from the Event Horizon to the Bondi Radius
• Radio observations of active galactic nuclei with mm-VLBI
• Simulations of imaging the event horizon of Sagittarius A* from space
• Stochastic Optics: A Scattering Mitigation Framework for Radio Interferometric Imaging
• Spacetime Tomography Using The Event Horizon Telescope
• Silhouettes of invisible black holes
• The Optics of Refractive Substructure
• The Galactic Center as a laboratory for theories of gravity and dark matter
• Quantifying Intrinsic Variability of Sagittarius A* using Closure Phase Measurements of the Event Horizon Telescope
• Evidence for a jet and outflow from Sgr A*: a continuum and spectral line study
• Asymmetric structure in Sgr A* at 3mm from closure phase measurements with VLBA, GBT and LMT
• Testing General Relativity with the Black Hole Shadow Size and Asymmetry of Sagittarius A*: Limitations from Interstellar Scattering
• 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
• MeqSilhouette : A mm-VLBI observation and signal corruption simulator
• VLBI imaging of black holes via second moment regularization
• Micro-arcsecond structure of Sagittarius A* revealed by high-sensitivity 86 GHz VLBI observations
• Interferometric Image Reconstruction using Closure Invariants and Machine Learning
• VLBA Observations of Strong Anisotripic Radio Scattering towards the Orion Nebula
• Visible shapes of black holes M87* and SgrA*