1.3 mm WAVELENGTH VLBI OF SAGITTARIUS A*: DETECTION OF TIME-VARIABLE EMISSION ON EVENT HORIZON SCALES

Fish, Vincent L.; Doeleman, Sheperd S.; Beaudoin, Christopher; Blundell, R.; Bolin, David E.; Bower, Geoffrey C.; Chamberlin, Richard; Freund, R.; Friberg, Per; Gurwell, M. A.; Honma, Mareki; Inoue, Makoto; Krichbaum, T. P.; Lamb, James W.; Marrone, Daniel P.; Moran, J. M.; Oyama, Tomoaki; Plambeck, R. L.; Primiani, Rurik A.; Rogers, A. E. E.; Smythe, D. L.; Soohoo, Jason; Strittmatter, P. A.; Tilanus, R. P. J.; Titus, Michael; Weintroub, Jonathan; Wright, M. C. H.; Woody, D. P.; Young, Ken; Ziurys, L. M.

doi:10.1088/2041-8205/727/2/l36

Cited by 198 publications

(287 citation statements)

References 34 publications

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“…This trend is not reproduced by the other triangles, but the observed and simulated values show that the highest deviations from zero-closure phases occur for triangles with an angle of maximum resolution close to the position angle of the detected secondary component. Fish et al (2011) detected closure phase values of (0 ± 40) • for Sgr A* using mm-VLBI at 1.3 mm with an Earth-scaled triangle of SMT-JCMT-CARMA. Broderick et al (2011) showed that accretion flow models can reproduce closure phase values up to ±30 • in some cases.…”

Section: Discussionmentioning

confidence: 85%

“…The short timescales suggest that this feature originates in a very compact region, possibly located close to the event horizon of the BH. Even though the detection of structures on these scales has not been achieved yet, Doeleman et al (2008Doeleman et al ( , 2009 and Fish et al (2011) have detected an intrinsic source structure of ∼40 µas on event-horizon scales using Very Long Baseline Interferometry (VLBI) at 0.7 mm and 1.3 mm.…”

Section: Introductionmentioning

confidence: 99%

“…While the flux variability of Sgr A* has been studied by many authors (e.g., Zhao et al 2003;Mauerhan et al 2005;Marrone et al 2006Marrone et al , 2008Doeleman et al 2008;Eckart et al 2008aEckart et al ,b,c, 2009Eckart et al , 2012Yusef-Zadeh et al 2008Li et al 2009;Kunneriath et al 2010;Sabha et al 2010;Zamaninasab et al 2010;Fish et al 2011;Miyazaki et al 2012), size measurements during flares have not been performed as frequently (e.g., Rogers et al 1994;Krichbaum et al 1998;Lo et al 1998;Doeleman et al 2001Doeleman et al , 2008Shen et al 2005Shen et al , 2006Huang et al 2007;Lu et al 2011;Bower et al 2014). Recently, Bower et al (2014) performed triggered multi-frequency VLBI observations of Sgr A* at NIR, X-ray, and 43 GHz that revealed an elliptical intrinsic source size of 35.4 × 12.6 R s with an rms variation of ∼5% and maximum peak-to-peak change of 15%.…”

Section: Introductionmentioning

confidence: 99%

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Wisps in the Galactic center: Near-infrared triggered observations of the radio source Sgr A* at 43 GHz

Rauch

Ros

Krichbaum

et al. 2016

A&A

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Context. The compact radio and near-infrared (NIR) source Sagittarius A* (Sgr A*) associated with the supermassive black hole in the Galactic center was observed at 7 mm in the context of a NIR triggered global Very Long Baseline Array (VLBA) campaign.Aims. Sgr A* shows variable flux densities ranging from radio through X-rays. These variations sometimes appear in spontaneous outbursts that are referred to as flares. Multi-frequency observations of Sgr A* provide access to easily observable parameters that can test the currently accepted models that try to explain these intensity outbursts. Methods. On May 16-18, 2012 Sgr A* has been observed with the VLBA at 7 mm (43 GHz) for 6 h each day during a global multiwavelength campaign. These observations were triggered by a NIR flare observed at the Very Large Telescope (VLT). Accurate flux densities and source morphologies were acquired. Results. The total 7 mm flux of Sgr A* shows only minor variations during its quiescent states on a daily basis of 0.06 Jy. An observed NIR flare on May 17 was followed ∼4.5 h later by an increase in flux density of 0.22 Jy at 43 GHz. This agrees well with the expected time delay of events that are casually connected by adiabatic expansion. Shortly before the peak of the radio flare, Sgr A* developed a secondary radio off-core feature at 1.5 mas toward the southeast. Even though the closure phases are too noisy to place actual constraints on this feature, a component at this scale together with a time delay of 4.5 ± 0.5 h between the NIR and radio flare provide evidence for an adiabatically expanding jet feature.

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Section: Discussionmentioning

confidence: 85%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Wisps in the Galactic center: Near-infrared triggered observations of the radio source Sgr A* at 43 GHz

Rauch

Ros

Krichbaum

et al. 2016

A&A

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“…Ongoing VLBI observations at 1.3 mm (mm-VLBI, Doeleman et al 2008;Fish et al 2011) may be able to distinguish variabilities caused by magnetic turbulence and adiabatic expansion. In models based on relativistic MHD simulations, the size and shape of the emission region do not change with variations in the total flux.…”

Section: Millimeter Vlbi Signature Of Adiabatic Expansionmentioning

confidence: 99%

“…Source structure on event-horizon scales has been detected by Doeleman et al (2008) and Fish et al (2011) by means of very long baseline interferometry (VLBI) at 1.3 mm wavelength. In the radio and millimeter wavelength regime, SgrA* is found to be variable (Zhao et al 2003;Mauerhan et al 2005;Eckart et al 2008;Marrone et al 2008;Li et al 2009;Yusef-Zadeh et al 2008.…”

Section: Introductionmentioning

confidence: 99%

Millimeter to X-ray flares from Sagittarius A*

Eckart

García-Marín

Vogel

et al. 2012

A&A

146

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Context. We report on new simultaneous observations and modeling of the millimeter, near-infrared, and X-ray flare emission of the source Sagittarius A* (SgrA*) associated with the super-massive (4 × 10 6 M ) black hole at the Galactic center. Aims. We study the applicability of the adiabatic synchrotron source expansion model and study physical processes giving rise to the variable emission of SgrA* from the radio to the X-ray domain. Methods. Our observations were carried out on 18 May 2009 using the NACO adaptive optics (AO) instrument at the European Southern Observatory's Very Large Telescope, the ACIS-I instrument aboard the Chandra X-ray Observatory, the LABOCA bolometer at the Atacama Pathfinder EXperiment (APEX), and the CARMA mm telescope array at Cedar Flat, California. Results. The X-ray flare had an excess 2−8 keV luminosity between 6 and 12×10 33 erg s −1 . The observations reveal flaring activity in all wavelength bands that can be modeled as the signal from an adiabatically expanding synchrotron self-Compton (SSC) component.Modeling of the light curves shows that the sub-mm follows the NIR emission with a delay of about three-quarters of an hour with an expansion velocity of about v exp ∼ 0.009c. We find source component sizes of around one Schwarzschild radius, flux densities of a few Janskys, and spectral indices α of about +1 (S (ν) ∝ ν −α ). At the start of the flare, the spectra of the two main components peak just short of 1 THz. To statistically explain the observed variability of the (sub-)mm spectrum of SgrA*, we use a sample of simultaneous NIR/X-ray flare peaks and model the flares using a synchrotron and SSC mechanism. Conclusions. These parameters suggest that either the adiabatically expanding source components have a bulk motion larger than v exp or the expanding material contributes to a corona or disk, confined to the immediate surroundings of SgrA*. For the bulk of the synchrotron and SSC models, we find synchrotron turnover frequencies in the range of 300−400 GHz. For the pure synchrotron models, this results in densities of relativistic particles of the order of 10 6.5 cm −3 and for the SSC models, the median densities are about one order of magnitude higher. However, to obtain a realistic description of the frequency-dependent variability amplitude of SgrA*, models with higher turnover frequencies and even higher densities are required.

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Greenland telescope project: Direct confirmation of black hole with sub‐millimeter VLBI

et al. 2014

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A 12 m diameter radio telescope will be deployed to the Summit Station in Greenland to provide direct confirmation of a Super Massive Black Hole (SMBH) by observing its shadow image in the active galaxy M87. The telescope (Greenland Telescope: GLT) is to become one of the Very Long Baseline Interferometry (VLBI) stations at sub-millimeter (submm) regime, providing the longest baseline >9000 km to achieve an exceptional angular resolution of 20 μas at 350 GHz, which will enable us to resolve the shadow size of~40 μas. The triangle with the longest baselines formed by the GLT, the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, and the Submillimeter Array (SMA) in Hawaii will play a key role for the M87 observations. We have been working on the image simulations based on realistic conditions for a better understanding of the possible observed images. In parallel, retrofitting of the telescope and the site developments are in progress. Based on 3 years of opacity monitoring at 225 GHz, our measurements indicate that the site is excellent for submm observations, comparable to the ALMA site. The GLT is also expected to make single-dish observations up to 1.5 THz.

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1.3 mm WAVELENGTH VLBI OF SAGITTARIUS A*: DETECTION OF TIME-VARIABLE EMISSION ON EVENT HORIZON SCALES

Cited by 198 publications

References 34 publications

Wisps in the Galactic center: Near-infrared triggered observations of the radio source Sgr A* at 43 GHz

Wisps in the Galactic center: Near-infrared triggered observations of the radio source Sgr A* at 43 GHz

Millimeter to X-ray flares from Sagittarius A*

Greenland telescope project: Direct confirmation of black hole with sub‐millimeter VLBI

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