Persistent Asymmetric Structure of Sagittarius A* on Event Horizon Scales

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Fish, Vincent
Broderick, Avery
Lu, Ru-Sen
Akiyama, Kazunori
Alef, Walter
Algaba, Juan
Asada, Keiichi
Beaudoin, Christopher
Bertarini, Alessandra
Bower, Geoffrey
Brinkerink, Christiaan
Cappallo, Roger
Chamberlin, Richard
Chan, Chi-Kwan
Crew, Geoffrey
Dexter, Jason
Dexter, Matt
Dzib, Sergio
Falcke, Heino
Freund, Robert
Friberg, Per
Greer, Christopher
Ho, Paul
Honma, Mareki
Inoue, Makoto
Johannsen, Tim
Kim, Junhan
Krichbaum, Thomas
Lamb, James
León-Tavares, Jonathan
Loinard, Laurent
MacMahon, David
Marrone, Daniel
Mościbrodzka, Monika
Ortiz-León, Gisela
Oyama, Tomoaki
Note: Order does not necessarily reflect citation order of authors.
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https://doi.org/10.3847/0004-637x/820/2/90Metadata
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Fish, Vincent L., Michael D. Johnson, Sheperd S. Doeleman, Avery E. Broderick, Dimitrios Psaltis, Ru-Sen Lu, Kazunori Akiyama, et al. 2016. “Persistent Asymmetric Structure of Sagittarius A* on Event Horizon Scales.” The Astrophysical Journal 820 (2) (March 22): 90. doi:10.3847/0004-637x/820/2/90. http://dx.doi.org/10.3847/0004-637x/820/2/90.Abstract
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 4 years. Closure phases, 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-degree 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 along the line of sight.Terms of Use
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http://nrs.harvard.edu/urn-3:HUL.InstRepos:30455610
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