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Title: PERSISTENT ASYMMETRIC STRUCTURE OF SAGITTARIUS A* ON EVENT HORIZON SCALES

The Galactic Center black hole Sagittarius A* (Sgr A*) is a prime observing target for the Event Horizon Telescope (EHT), which can resolve the 1.3 mm emission from this source on angular scales comparable to that of the general relativistic shadow. Previous EHT observations have used visibility amplitudes to infer the morphology of the millimeter-wavelength emission. Potentially much richer source information is contained in the phases. We report on 1.3 mm phase information on Sgr A* obtained with the EHT on a total of 13 observing nights over four years. Closure phases, which are the sum of visibility phases along a closed triangle of interferometer baselines, are used because they are robust against phase corruptions introduced by instrumentation and the rapidly variable atmosphere. The median closure phase on a triangle including telescopes in California, Hawaii, and Arizona is nonzero. This result conclusively demonstrates that the millimeter emission is asymmetric on scales of a few Schwarzschild radii and can be used to break 180° rotational ambiguities inherent from amplitude data alone. The stability of the sign of the closure phase over most observing nights indicates persistent asymmetry in the image of Sgr A* that is not obscured by refraction due to interstellar electrons alongmore » the line of sight.« less
Authors:
; ; ; ; ;  [1] ; ; ; ;  [2] ;  [3] ; ;  [4] ; ;  [5] ;  [6] ;  [7] ;  [8] ;  [9] ;  [10] more »; « less
  1. Massachusetts Institute of Technology, Haystack Observatory, Route 40, Westford, MA 01886 (United States)
  2. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
  3. Perimeter Institute for Theoretical Physics, 31 Caroline Street North, Waterloo, ON N2L 2Y5 (Canada)
  4. Steward Observatory and Department of Astronomy, University of Arizona, 933 North Cherry Ave., Tucson, AZ 85721-0065 (United States)
  5. Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn (Germany)
  6. Korea Astronomy and Space Science Institute, 776 Daedeokdae-ro, Yuseong-gu, Daejeon 305-348 (Korea, Republic of)
  7. Institute of Astronomy and Astrophysics, Academia Sinica, P.O. Box 23-141, Taipei 10617, Taiwan (China)
  8. Academia Sinica Institute for Astronomy and Astrophysics, 645 N. A‘ohōkū Place, Hilo, HI 96720 (United States)
  9. Department of Astrophysics/IMAPP, Radboud University Nijmegen, P.O. Box 9010, 6500 GL, Nijmegen (Netherlands)
  10. Caltech Submillimeter Observatory, 111 Nowelo Street, Hilo, HI 96720 (United States)
Publication Date:
OSTI Identifier:
22518561
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 820; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; AMPLITUDES; ASYMMETRY; BLACK HOLES; COMPARATIVE EVALUATIONS; EMISSION; IMAGES; MILKY WAY; MORPHOLOGY; RELATIVISTIC RANGE; SCHWARZSCHILD RADIUS; TELESCOPES; VISIBILITY