First 230 GHz VLBI fringes on 3C 279 using the APEX Telescope

Wagner, Jan; Roy, A. L.; Krichbaum, T. P.; Alef, W.; Bansod, A.; Bertarini, Alessandra; Güsten, R.; Graham, D. A.; Hodgson, Jeffrey A.; Martens, Rhonda; Menten, K. M.; Muders, D.; Rottmann, Helge; Tuccari, G.; Weiß, A.; Wieching, G.; Wunderlich, Michael T.; Zensus, J. A.; Araneda, J.P.; Arriagada, Oriel; Cantzler, Michael; Durán, C.; Montenegro‐Montes, F. M.; Olivares, R.; Caro, Patricio; Bergman, P.; Conway, J.; Haas, Rüdiger; Johansson, Jan M.; Lindqvist, Michael; Olofsson, H.; Pantaleev, Miroslav; Buttaccio, S.; Cappallo, R. J.; Crew, G. B.; Doeleman, Sheperd S.; Fish, Vincent L.; Lu, Ru-Sen; Ruszczyk, Chet; Soohoo, Jason; Titus, Michael; Freund, R.; Marrone, Daniel P.; Strittmatter, P. A.; Ziurys, L. M.; Blundell, R.; Primiani, Rurik A.; Weintroub, Jonathan; Young, Ken; Bremer, M.; Sánchez, Salvador; Marscher, A. P.; Chilson, Ryan; Asada, Keiichi; Inoue, Makoto

doi:10.1051/0004-6361/201423613

Cited by 17 publications

(9 citation statements)

References 14 publications

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“…Nonzero closure phases have been detected on bright quasar sources with the EHT and used to model the structure of these sources (Lu et al 2012(Lu et al , 2013Akiyama et al 2015;Wagner et al 2015), but the relative weakness of SgrA * has thus far only allowed a weak upper limit to be placed on the absolute value of its closure phase on the California-Hawaii-Arizona triangle (Fish et al 2011). In this paper we report on detections of nonzero closure phases in SgrA * , providing the first direct indication of asymmetric emission near the black hole.…”

Section: Closure Phasesmentioning

confidence: 86%

Persistent Asymmetric Structure of Sagittarius A* on Event Horizon Scales

Fish

Johnson

Doeleman

et al. 2016

ApJ

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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 along the line of sight.

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Section: Closure Phasesmentioning

confidence: 86%

Persistent Asymmetric Structure of Sagittarius A* on Event Horizon Scales

Fish

Johnson

Doeleman

et al. 2016

ApJ

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“…Development and deployment of broadband VLBI systems (Whitney et al 2013;Vertatschitsch et al 2015) led to data recording rates that now exceed those of typical cm-VLBI arrays by more than an order of magnitude. Parallel efforts to support infrastructure upgrades at additional VLBI sites, including the Atacama Large Millimeter/submillimeter Array (ALMA; Matthews et al 2018;Goddi et al 2019) and the Atacama Pathfinder Experiment telescope (APEX) in Chile (Wagner et al 2015), the Large Millimeter Telescope Alfonso Serrano (LMT) in Mexico (Ortiz-León et al 2016), the IRAM 30 m telescope on Pico Veleta (PV) in Spain (Greve et al 1995), the Submillimeter Telescope Observatory in Arizona (SMT; Baars et al 1999), the James Clerk Maxwell Telescope (JCMT) and the Submillimeter Array (SMA) in Hawai'i (Doeleman et al 2008;Primiani et al 2016;Young et al 2016), and the South Pole Telescope (SPT) in Antarctica (Kim et al 2018a), extended the range of EHT baselines and coverage, and the overall collecting area of the array. These developments increased the sensitivity of the EHT by a factor of ∼30 over early experiments that confirmed horizon-scale structures in M87 * and Sgr A * (Doeleman et al 2008(Doeleman et al , 2012Akiyama et al 2015;Johnson et al 2015;Fish et al 2016;Lu et al 2018).…”

Section: The Event Horizon Telescopementioning

confidence: 99%

First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole

Akiyama¹,

Alberdi²,

Alef³

et al. 2019

ApJL

3,022

1,428

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When surrounded by a transparent emission region, black holes are expected to reveal a dark shadow caused by gravitational light bending and photon capture at the event horizon. To image and study this phenomenon, we have assembled the Event Horizon Telescope, a global very long baseline interferometry array observing at a wavelength of 1.3 mm. This allows us to reconstruct event-horizon-scale images of the supermassive black hole candidate in the center of the giant elliptical galaxy M87. We have resolved the central compact radio source as an asymmetric bright emission ring with a diameter of 42±3 μas, which is circular and encompasses a central depression in brightness with a flux ratio 10:1. The emission ring is recovered using different calibration and imaging schemes, with its diameter and width remaining stable over four different observations carried out in different days. Overall, the observed image is consistent with expectations for the shadow of a Kerr black hole as predicted by general relativity. The asymmetry in brightness in the ring can be explained in terms of relativistic beaming of the emission from a plasma rotating close to the speed of light around a black hole. We compare our images to an extensive library of ray-traced general-relativistic magnetohydrodynamic simulations of black holes and derive a central mass of M=(6.5±0.7)×10 9 M e . Our radiowave observations thus provide powerful evidence for the presence of supermassive black holes in centers of galaxies and as the central engines of active galactic nuclei. They also present a new tool to explore gravity in its most extreme limit and on a mass scale that was so far not accessible.

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“…The first issue is reconstructing the image only from the visibility amplitudes and closure phases (see Section 2.1), which have been the standard data products of EHT observations (Lu et al 2012(Lu et al , 2013Akiyama et al 2015;Wagner et al 2015;Fish et al 2016) and optical/infrared interferometry. The algorithm of Honma et al (2014) is applicable only for full-complex visibilities, which are the usual data products from longer-wavelength radio interferometers.…”

Section: Introductionmentioning

confidence: 99%

Imaging the Schwarzschild-radius-scale Structure of M87 with the Event Horizon Telescope Using Sparse Modeling

Akiyama

Kuramochi

Ikeda

et al. 2017

ApJ

144

129

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We propose a new imaging technique for radio and optical/infrared interferometry. The proposed technique reconstructs the image from the visibility amplitude and closure phase, which are standard data products of shortmillimeter very long baseline interferometers such as the Event Horizon Telescope (EHT) and optical/infrared interferometers, by utilizing two regularization functions: the ℓ 1 -norm and total variation (TV) of the brightness distribution. In the proposed method, optimal regularization parameters, which represent the sparseness and effective spatial resolution of the image, are derived from data themselves using cross-validation (CV). As an application of this technique, we present simulated observations of M87 with the EHT based on four physically motivated models. We confirm that ℓ 1 +TV regularization can achieve an optimal resolution of ∼20%-30% of the diffraction limit λ/D max , which is the nominal spatial resolution of a radio interferometer. With the proposed technique, the EHT can robustly and reasonably achieve super-resolution sufficient to clearly resolve the black hole shadow. These results make it promising for the EHT to provide an unprecedented view of the event-horizon-scale structure in the vicinity of the supermassive black hole in M87 and also the Galactic center Sgr A * .

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First 230 GHz VLBI fringes on 3C 279 using the APEX Telescope

Cited by 17 publications

References 14 publications

Persistent Asymmetric Structure of Sagittarius A* on Event Horizon Scales

Persistent Asymmetric Structure of Sagittarius A* on Event Horizon Scales

First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole

Imaging the Schwarzschild-radius-scale Structure of M87 with the Event Horizon Telescope Using Sparse Modeling

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