Persistent Asymmetric Structure of Sagittarius A* on Event Horizon Scales
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.
Keywords
Cite
@article{arxiv.1602.05527,
title = {Persistent Asymmetric Structure of Sagittarius A* on Event Horizon Scales},
author = {Vincent L. Fish and Michael D. Johnson and Sheperd S. Doeleman and Avery E. Broderick and Dimitrios Psaltis and Ru-Sen Lu and Kazunori Akiyama and Walter Alef and Juan Carlos Algaba and Keiichi Asada and Christopher Beaudoin and Alessandra Bertarini and Lindy Blackburn and Ray Blundell and Geoffrey C. Bower and Christiaan Brinkerink and Roger Cappallo and Andrew A. Chael and Richard Chamberlin and Chi-Kwan Chan and Geoffrey B. Crew and Jason Dexter and Matt Dexter and Sergio A. Dzib and Heino Falcke and Robert Freund and Per Friberg and Christopher H. Greer and Mark A. Gurwell and Paul T. P. Ho and Mareki Honma and Makoto Inoue and Tim Johannsen and Junhan Kim and Thomas P. Krichbaum and James Lamb and Jonathan León-Tavares and Abraham Loeb and Laurent Loinard and David MacMahon and Daniel P. Marrone and James M. Moran and Monika Mościbrodzka and Gisela N. Ortiz-León and Tomoaki Oyama and Feryal Özel and Richard L. Plambeck and Nicolas Pradel and Rurik A. Primiani and Alan E. E. Rogers and Katherine Rosenfeld and Helge Rottmann and Alan L. Roy and Chester Ruszczyk and Daniel L. Smythe and Jason SooHoo and Justin Spilker and Jordan Stone and Peter Strittmatter and Remo P. J. Tilanus and Michael Titus and Laura Vertatschitsch and Jan Wagner and John F. C. Wardle and Jonathan Weintroub and David Woody and Melvyn Wright and Paul Yamaguchi and André Young and Ken H. Young and J. Anton Zensus and Lucy M. Ziurys},
journal= {arXiv preprint arXiv:1602.05527},
year = {2016}
}
Comments
11 pages, accepted to ApJ