The Intrinsic Two-Dimensional Size of Sagittarius A*

Bower, Geoffrey C.; Markoff, Sera; Brunthaler, A.; Law, Casey J.; Falcke, H.; Maitra, D.; Clavel, M.; Goldwurm, A.; Morris, Mark; Witzel, G.; Meyer, L.; Ghez, A. M.

doi:10.1088/0004-637x/790/1/1

Cited by 55 publications

(77 citation statements)

References 58 publications

(105 reference statements)

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“…screen (e.g., Bower et al 2014), the nature of the radio emission near the central supermassive black hole (SMBH) remains hidden, so it is somewhat difficult to probe its putative jet intrinsic geometry and properties. On the other hand, the radio core of M 87 is resolved into a clear jet structure and can be readily used as a laboratory for testing various theoretical models of the magnetized plasma flows onto compact objects.…”

Section: Introductionmentioning

confidence: 99%

General relativistic magnetohydrodynamical simulations of the jet in M 87

Mościbrodzka

Falcke

Shiokawa

2016

A&A

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280

312

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Context. The connection between black hole, accretion disk, and radio jet can be constrained best by fitting models to observations of nearby low-luminosity galactic nuclei, in particular the well-studied sources Sgr A* and M 87. There has been considerable progress in modeling the central engine of active galactic nuclei by an accreting supermassive black hole coupled to a relativistic plasma jet. However, can a single model be applied to a range of black hole masses and accretion rates? Aims. Here we want to compare the latest three-dimensional numerical model, originally developed for Sgr A* in the center of the Milky Way, to radio observations of the much more powerful and more massive black hole in M 87. Methods. We postprocess three-dimensional GRMHD models of a jet-producing radiatively inefficient accretion flow around a spinning black hole using relativistic radiative transfer and ray-tracing to produce model spectra and images. As a key new ingredient in these models, we allow the proton-electron coupling in these simulations depend on the magnetic properties of the plasma. Results. We find that the radio emission in M 87 is described well by a combination of a two-temperature accretion flow and a hot single-temperature jet. Most of the radio emission in our simulations comes from the jet sheath. The model fits the basic observed characteristics of the M 87 radio core: it is "edge-brightened", starts subluminally, has a flat spectrum, and increases in size with wavelength. The best fit model has a mass-accretion rate ofṀ ∼ 9 × 10 −3 M yr −1 and a total jet power of P j ∼ 10 43 erg s −1 . Emission at λ = 1.3 mm is produced by the counter-jet close to the event horizon. Its characteristic crescent shape surrounding the black hole shadow could be resolved by future millimeter-wave VLBI experiments. Conclusions. The model was successfully derived from one for the supermassive black hole in the center of the Milky Way by appropriately scaling mass and accretion rate. This suggests the possibility that this model could also apply to a wider range of low-luminosity black holes.

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Section: Introductionmentioning

confidence: 99%

General relativistic magnetohydrodynamical simulations of the jet in M 87

Mościbrodzka

Falcke

Shiokawa

2016

A&A

Self Cite

280

312

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“…It is expected that the λ 2 -dependency breaks at around 43 GHz and the intrinsic source size is no longer dominated by scatter broadening and thus reveales its true structure (Krichbaum et al 1998(Krichbaum et al , 2006Lo et al 1998;Doeleman et al 2001;Bower et al 2004Bower et al , 2006Shen et al 2005), while Bower et al (2014) reported that strong interstellar scattering is still present at 7 mm. Therefore, observations of Sgr A* with 7 mm VLBI are of particular interest to study its source size and morphology.…”

Section: Introductionmentioning

confidence: 99%

“…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%. Akiyama et al (2013) found even stronger fluctuations of its intrinsic size of 19% at 43 GHz based on VERA observations of the emitting region.…”

Section: Introductionmentioning

confidence: 99%

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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“…The Astrophysical Journal, 819:60 (25pp), 2016 March 1 doi:10.3847/0004-637X/819/1/60 sources, scatter broadening, and intrinsic temporal variability of SgrA * on hourly timescales (e.g., Bower et al 2014). Here we present sensitive observations of the Galactic center at multiple radio frequencies, obtained using the improved broadband capability of the Very Large Array (VLA), finding new radio structures interpreted to be associated with Sgr A * activity.…”

Section: Introductionmentioning

confidence: 99%

SGR A* and Its Environment: Low-Mass Star Formation, the Origin of X-Ray Gas and Collimated Outflow

Yusef‐Zadeh

Wardle

Schödel

et al. 2016

ApJ

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We present high-resolution multiwavelength radio continuum images of the region within 150″ of SgrA * , revealing a number of new extended features and stellar sources in this region. First, we detect a continuous 2″ east-west ridge of radio emission, linking SgrA * and a cluster of stars associated with IRS 13 N and IRS 13E. The ridge suggests that an outflow of east-west blob-like structures is emerging from SgrA * . In particular, we find arc-like radio structures within the ridge with morphologies suggestive of photoevaporative protoplanetary disks. We use infrared K s and L′ fluxes to show that the emission has similar characteristics to those of a protoplanetary disk irradiated by the intense radiation field at the Galactic center. This suggests that star formation has taken place within the S-cluster 2″ from SgrA * . We suggest that the diffuse X-ray emission associated with Sgr A * is due to an expanding hot wind produced by the mass loss from B-type main sequence stars, and/or the disks of photoevaporation of low mass young stellar objects (YSOs) at a rate of ∼10 −6  M yr −1 . The proposed model naturally reduces the inferred accretion rate and is an alternative to the inflow-outflow style models to explain the underluminous nature of Sgr A * . Second, on a scale of 5″ from Sgr A * , we detect new cometary radio and infrared sources at a position angle PA∼50°which is similar to that of two other cometary sources X3 and X7, all of which face Sgr A * . In addition, we detect a striking tower of radio emission at a PA∼50°-60°along the major axis of the Sgr A East supernova remnant shell on a scale of 150″ from Sgr A * . We suggest that the cometary sources and the tower feature are tracing interaction sites of a mildly relativistic jet from Sgr A * with the atmosphere of stars and the nonthermal Sgr A East shell at a PA∼50°-60°with´-, and opening angle 10°. Lastly, we suggest that the east-west ridge of radio emission traces an outflow that is potentially associated with past flaring activity from Sgr A * . The position angle of the outflow driven by flaring activity is close to −90°.

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The Intrinsic Two-Dimensional Size of Sagittarius A*

Cited by 55 publications

References 58 publications

General relativistic magnetohydrodynamical simulations of the jet in M 87

General relativistic magnetohydrodynamical simulations of the jet in M 87

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

SGR A* and Its Environment: Low-Mass Star Formation, the Origin of X-Ray Gas and Collimated Outflow

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