Person:
Chael, Andrew

Profile Picture

Email Address

AA Acceptance Date

Birth Date

Research Projects

Organizational Units

Job Title

Last Name

Chael

First Name

Andrew

Name

Chael, Andrew

Filters

2015 - 20162

Settings

Author's Publications: search.filters.isAuthorOfPublication.7ceb7bb9-e7f7-40aa-aad5-6fa51ba8d096

Search Results

Now showing 1 - 2 of 2
  • Thumbnail Image
    Publication
    Persistent Asymmetric Structure of Sagittarius A* on Event Horizon Scales
    (American Astronomical Society, 2016) Fish, Vincent; Johnson, Michael; Doeleman, Sheperd; Broderick, Avery; Psaltis, Dimitrios; Lu, Ru-Sen; Akiyama, Kazunori; Alef, Walter; Algaba, Juan; Asada, Keiichi; Beaudoin, Christopher; Bertarini, Alessandra; Blackburn, Lindy; Blundell, Raymond; Bower, Geoffrey; Brinkerink, Christiaan; Cappallo, Roger; Chael, Andrew; Chamberlin, Richard; Chan, Chi-Kwan; Crew, Geoffrey; Dexter, Jason; Dexter, Matt; Dzib, Sergio; Falcke, Heino; Freund, Robert; Friberg, Per; Greer, Christopher; Gurwell, Mark; Ho, Paul; Honma, Mareki; Inoue, Makoto; Johannsen, Tim; Kim, Junhan; Krichbaum, Thomas; Lamb, James; León-Tavares, Jonathan; Loeb, Abraham; Loinard, Laurent; MacMahon, David; Marrone, Daniel; Moran, James; Mościbrodzka, Monika; Ortiz-León, Gisela; Oyama, Tomoaki; Özel, Feryal
    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.
  • Thumbnail Image
    Publication
    Resolved magnetic-field structure and variability near the event horizon of Sagittarius A
    (American Association for the Advancement of Science (AAAS), 2015) Johnson, Michael; Fish, V. L.; Doeleman, Sheperd; Marrone, D. P.; Plambeck, R. L.; Wardle, J. F. C.; Akiyama, K.; Asada, K.; Beaudoin, C.; Blackburn, Lindy; Blundell, Raymond; Bower, G. C.; Brinkerink, C.; Broderick, A. E.; Cappallo, R.; Chael, Andrew; Crew, G. B.; Dexter, J.; Dexter, M.; Freund, R.; Friberg, P.; Gold, R.; Gurwell, M. A.; Ho, P. T. P.; Honma, M.; Inoue, M.; Kosowsky, Michael; Krichbaum, T. P.; Lamb, J.; Loeb, Abraham; Lu, R.-S.; MacMahon, D.; McKinney, J. C.; Moran, James; Narayan, Ramesh; Primiani, Rurik; Psaltis, D.; Rogers, A. E. E.; Rosenfeld, Katherine; SooHoo, J.; Tilanus, R. P. J.; Titus, M.; Vertatschitsch, L.; Weintroub, Jonathan; Wright, M.; Young, Ken; Zensus, J. A.; Ziurys, L. M.
    Near a black hole, differential rotation of a magnetized accretion disk is thought to produce an instability that amplifies weak magnetic fields, driving accretion and outflow. These magnetic fields would naturally give rise to the observed synchrotron emission in galaxy cores and to the formation of relativistic jets, but no observations to date have been able to resolve the expected horizonscale magnetic-field structure. We report interferometric observations at 1.3- millimeter wavelength that spatially resolve the linearly polarized emission from the Galactic Center supermassive black hole, Sagittarius A*. We have found evidence for partially ordered fields near the event horizon, on scales of ∼6 Schwarzschild radii, and we have detected and localized the intra-hour variability associated with these fields.