PERSISTENT ASYMMETRIC STRUCTURE of SAGITTARIUS A∗ on EVENT HORIZON SCALES

Vincent L. Fish, Michael D. Johnson, Sheperd S. Doeleman, Avery E. Broderick, Dimitrios Psaltis, Ru Sen Lu, Kazunori Akiyama, Walter Alef, Juan Carlos Algaba, Keiichi Asada, Christopher Beaudoin, Alessandra Bertarini, Lindy Blackburn, Ray Blundell, Geoffrey C. Bower, Christiaan Brinkerink, Roger Cappallo, Andrew A. Chael, Richard Chamberlin, Chi Kwan ChanGeoffrey B. Crew, Jason Dexter, Matt Dexter, Sergio A. Dzib, Heino Falcke, Robert Freund, Per Friberg, Christopher H. Greer, Mark A. Gurwell, Paul T.P. Ho, Mareki Honma, Makoto Inoue, Tim Johannsen, Junhan Kim, Thomas P. Krichbaum, James Lamb, Jonathan León-Tavares, Abraham Loeb, Laurent Loinard, David Macmahon, Daniel P. Marrone, James M. Moran, Monika Mościbrodzka, Gisela N. Ortiz-León, Tomoaki Oyama, Feryal Zel, Richard L. Plambeck, Nicolas Pradel, Rurik A. Primiani, Alan E.E. Rogers, Katherine Rosenfeld, Helge Rottmann, Alan L. Roy, Chester Ruszczyk, Daniel L. Smythe, Jason Soohoo, Justin Spilker, Jordan Stone, Peter Strittmatter, Remo P.J. Tilanus, Michael Titus, Laura Vertatschitsch, Jan Wagner, John F.C. Wardle, Jonathan Weintroub, David Woody, Melvyn Wright, Paul Yamaguchi, André Young, Ken H. Young, J. Anton Zensus, Lucy M. Ziurys

Research output: Contribution to journalArticle

53 Scopus citations

Abstract

The Galactic Center black hole SagittariusA∗ (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 SgrA∗ 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 SgrA∗ that is not obscured by refraction due to interstellar electrons along the line of sight.

Original languageEnglish (US)
Article number90
JournalAstrophysical Journal
Volume820
Issue number2
DOIs
StatePublished - Apr 1 2016

Keywords

  • Galaxy: center
  • submillimeter: general
  • techniques: high angular resolution
  • techniques: interferometric

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Fish, V. L., Johnson, M. D., Doeleman, S. S., Broderick, A. E., Psaltis, D., Lu, R. S., Akiyama, K., Alef, W., Algaba, J. C., Asada, K., Beaudoin, C., Bertarini, A., Blackburn, L., Blundell, R., Bower, G. C., Brinkerink, C., Cappallo, R., Chael, A. A., Chamberlin, R., ... Ziurys, L. M. (2016). PERSISTENT ASYMMETRIC STRUCTURE of SAGITTARIUS A∗ on EVENT HORIZON SCALES. Astrophysical Journal, 820(2), [90]. https://doi.org/10.3847/0004-637X/820/2/90