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Detection of Intrinsic Source Structure at ~3 Schwarzschild Radii with Millimeter-VLBI Observations of SAGITTARIUS A*

Lu, Ru-Sen and Lamb, James (2018) Detection of Intrinsic Source Structure at ~3 Schwarzschild Radii with Millimeter-VLBI Observations of SAGITTARIUS A*. Astrophysical Journal, 859 (1). Art. No. 60. ISSN 1538-4357.

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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 uv coverage in the N–S direction, and leads to a spatial resolution of ~30 μas (~3 Schwarzschild radii) for Sgr A*. The source is detected even at the longest baselines with visibility amplitudes of ~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 ~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 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.

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Lu, Ru-Sen0000-0002-7692-7967
Additional Information:© 2018 The American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2017 December 18; revised 2018 March 28; accepted 2018 April 10; published 2018 May 24. We thank the anonymous referee for constructive comments that improved the paper. The authors thank the APEX observatory staff and the APEX team at the MPIfR for their support. In particular, we appreciate the help of R. Güsten, D. Muders, and A. Weiss. R.-S.L. thanks Dr. Lei Chen for fruitful discussion on the data analysis and Dr. R. W. Porcas and Dr. N. R. MacDonald for very useful comments and discussions. K.A. thanks Prof. Koji Hukushima, Prof. Masato Okada, and Dr. Kenji Nagata for useful advice and suggestions on the development of our modeling code using the Exchange Monte Carlo method adopted in this work. H.F. acknowledges funding from the European Research Council (ERC) Synergy Grant "BlackHoleCam" (Grant 610058). E.R. acknowledges support from the Spanish MINECO through grants AYA2012-38491-C02-01 and AYA2015-63939-C2-2-P and from the Generalitat Valenciana grant PROMETEOII/2014/057. Based on observations with the Atacama Pathfinder EXperiment (APEX) telescope (under project ID 091.F-9312(A)). APEX is a collaboration between the Max Planck Institute for Radio Astronomy, the European Southern Observatory, and the Onsala Space Observatory. The Submillimeter Array is a joint project between the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics and is funded by the Smithsonian Institution and the Academia Sinica. The JCMT was operated by the Joint Astronomy Centre on behalf of the Science and Technology Facilities Council of the UK, the Netherlands Organisation for Scientific Research, and the National Research Council of Canada. Funding for ongoing CARMA development and operations was supported by the NSF and CARMA partner universities. Facility: EHT - .
Funding AgencyGrant Number
European Research Council (ERC)610058
Ministerio de Economía, Industria y Competitividad (MINECO)AYA2012-38491-C02-01
Ministerio de Economía, Industria y Competitividad (MINECO)AYA2015-63939-C2-2-P
Generalitat ValencianaPROMETEOII/2014/057
Smithsonian InstitutionUNSPECIFIED
Academia SinicaUNSPECIFIED
CARMA partner universitiesUNSPECIFIED
Subject Keywords:Galaxy: center – submillimeter: general – techniques: high angular resolution – techniques: interferometric
Record Number:CaltechAUTHORS:20180613-112956599
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Official Citation:Ru-Sen Lu et al 2018 ApJ 859 60
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:87067
Deposited By: Tony Diaz
Deposited On:13 Jun 2018 18:52
Last Modified:13 Jun 2018 18:52

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