Persistent Asymmetric Structure of Sagittarius A* on Event Horizon Scales

Fish, Vincent L.; Johnson, Michael D.; Doeleman, Sheperd S.; Broderick, Avery E.; Psaltis, Dimitrios; Lu, Ru-Sen; Akiyama, Kazunori; Alef, W.; Algaba, Juan Carlos; Asada, Keiichi; Beaudoin, Christopher; Bertarini, Alessandra; Blackburn, L.; Blundell, R.; Bower, Geoffrey C.; Brinkerink, Christiaan D.; Cappallo, R. J.; Chael, Andrew; Chamberlin, Richard; Chan, Chi-kwan; Crew, G. B.; Dexter, Jason; Dexter, Matt; Dzib, S. A.; Falcke, H.; Freund, R.; Friberg, Per; Greer, Christopher H.; Gurwell, M. A.; Ho, P. T. P.; Honma, Mareki; Inoue, Makoto; Johannsen, Tim; Kim, Junhan; Krichbaum, T. P.; Lamb, James W.; León-Tavares, J.; Loeb, Abraham; Loinard, Laurent; MacMahon, David H. E.; Marrone, Daniel P.; Moran, J. M.; Mościbrodzka, Monika; Ortiz-León, Gisela N.; Oyama, Tomoaki; Özel, Feryal; Plambeck, R. L.; Pradel, Nicolas; Primiani, Rurik A.; Rogers, A. E. E.; Rosenfeld, Katherine; Rottmann, Helge; Roy, A. L.; Ruszczyk, Chet; Smythe, D. L.; Soohoo, Jason; Spilker, Justin; Stone, Jordan; Strittmatter, P. A.; Tilanus, R. P. J.; Titus, Michael; Vertatschitsch, Laura; Wagner, Jan; Wardle, J. F. C.; Weintroub, Jonathan; Woody, D. P.; Wright, M. C. H.; Yamaguchi, Paul; Young, André; Young, Ken; Zensus, J. A.; Ziurys, L. M.

doi:10.3847/0004-637x/820/2/90

Cited by 78 publications

(93 citation statements)

References 73 publications

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“…Fish et al (2011);Doeleman et al (2009) Doeleman et al (2009 show that source components orbiting the SMBH can be detected even with non-imaging EHT data sets, and Fish et al (2011Fish et al ( , 2016 confirm strong evidence for time-variable changes in SgrA* on scales of a few Schwarzschild radii using EHT observations. With these refined analysis tools and successful pre-cursor observations, the prospects for directly probing the event horizon with the EHT are excellent, and present exciting opportunities to constrain physics and dynamics at the black hole boundary, as well as potential tests of GR, in conjunction with NIR observations (Psaltis et al, 2016a).…”

Section: Sizementioning

confidence: 64%

The Milky Way’s Supermassive Black Hole: How Good a Case Is It?

Eckart

Hüttemann²,

Kiefer³

et al. 2017

Found Phys

122

105

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The compact and, with 4.3±0.3×106 M ⊙ , very massive object located at the center of the Milky Way is currently the very best candidate for a supermassive black hole (SMBH) in our immediate vicinity. The strongest evidence for this is provided by measurements of stellar orbits, variable X-ray emission, and strongly variable polarized near-infrared emission from the location of the radio source Sagittarius A* (SgrA*) in the middle of the central stellar cluster. Simultaneous near-infrared and X-ray observations of SgrA* have revealed insights into the emission mechanisms responsible for the powerful near-infrared and X-ray flares from within a few tens to one hundred Schwarzschild radii of such a putative SMBH at the center of the Milky Way. If SgrA* is indeed a SMBH it will, in projection onto the sky, have the largest event horizon and will certainly be the first and most important target of the Event Horizon Telescope (EHT) Very Long Baseline Interferometry (VLBI) observations currently being prepared. These observations in combination with the infrared interferometry experiment GRAVITY at the Very Large Telescope Interferometer (VLTI) and other experiments across the electromagnetic spectrum might yield proof for the presence of a black hole at the center of the Milky Way. The large body of evidence continues to discriminate the identification of SgrA* as a SMBH from alternative possibilities. It is, however, unclear when the ever mounting evidence for SgrA* being associated with a SMBH will suffice as a convincing proof. Additional compelling evidence may come from future gravitational wave observatories. This manuscript reviews the observational facts, theoretical grounds and conceptual aspects for the case of SgrA* being a black hole. We treat theory and observations in the framework of the philosophical discussions about "(Anti)Realism and Underdetermination", as this line of arguments allows us to describe the situation in observational astrophysics with respect to supermassive black holes. Questions concerning the existence of supermassive black holes and in particular SgrA* are discussed using causation as an indispensable element. We show that the results of our investigation are convincingly mapped out by this combination of concepts.

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Section: Sizementioning

confidence: 64%

The Milky Way’s Supermassive Black Hole: How Good a Case Is It?

Eckart

Hüttemann²,

Kiefer³

et al. 2017

Found Phys

122

105

View full text Add to dashboard Cite

show abstract

“…The simple model is useful for future exploration of the parameter space, providing a quick, flexible overview of the most likely flow dynamic ranges. We plan to perform further detailed analysis, using the closure phase data recently published in Fish et al (2016). Their data will prove useful to constrain the dynamics of the accretion flow, as well as the black hole spin, its inclination angle, and position angle.…”

Section: Summary and Future Perspectivementioning

confidence: 99%

“…Very long baseline interferometry (VLBI) observations of the nearest supermassive black hole, Sagittarius A * (Sgr A * ), have provided valuable information concerning the emission region within a few Schwarzschild radii of the black hole (e.g., Doeleman et al 2008;Fish et al 2011Fish et al , 2016. The extremely dim luminosity of Sgr A * (~-L 10 9 Edd , where L Edd is the Eddington luminosity) suggests that the accretion flow around the black hole is in the radiatively inefficient accretion flow (RIAF) regime (e.g., Narayan et al 1995;Manmoto et al 1997;Özel et al 2000;Yuan et al 2003).…”

Section: Introductionmentioning

confidence: 99%

The Effects of Accretion Flow Dynamics on the Black Hole Shadow of Sagittarius A*

Akiyama

Asada

2016

ApJ

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A radiatively inefficient accretion flow (RIAF), which is commonly characterized by its sub-Keplerian nature, is a favored accretion model for the supermassive black hole at the Galactic center, Sagittarius A * . To investigate the observable features of an RIAF, we compare the modeled shadow images, visibilities, and spectra of three flow models with dynamics characterized by (i) a Keplerian shell that is rigidly rotating outside the innermost stable circular orbit (ISCO) and infalling with a constant angular momentum inside ISCO, (ii) a sub-Keplerian motion, and (iii) a free-falling motion with zero angular momentum at infinity. At near-millimeter wavelengths, the emission is dominated by the flow within several Schwarzschild radii. The energy shift due to these flow dynamics becomes important and distinguishable, suggesting that the flow dynamics are an important model parameter for interpreting the millimeter/sub-millimeter very long baseline interferometric observations with the forthcoming, fully assembled Event Horizon Telescope (EHT). As an example, we demonstrate that structural variations of Sagittarius A * on event horizon-scales detected in previous EHT observations can be explained by the nonstationary dynamics of an RIAF.

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“…An accurate model for the microphysics is even more important as our observations are reaching a very high level of resolution (especially with the Event Horizon Telescope returning results, e.g. Fish et al 2016). Interpreting the high quality data requires taking into account particle distributions in the medium and understanding what the physical plasma conditions are.…”

Section: Introductionmentioning

confidence: 99%

Using infrared/X-ray flare statistics to probe the emission regions near the event horizon of Sgr A*

Dibi

Markoff

Belmont

et al. 2016

Mon. Not. R. Astron. Soc.

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The supermassive black hole at the centre of the Galaxy flares at least daily in the infrared (IR) and X-ray bands, yet the process driving these flares is still unknown. So far detailed analysis has only been performed on a few bright flares. In particular, the broadband spectral modelling suffers from a strong lack of simultaneous data. However, new monitoring campaigns now provide data on thousands of flaring events, allowing a statistical analysis of the flare properties. In this paper, we investigate the X-ray and IR flux distributions of the flare events.Using a self-consistent calculation of the particle distribution, we model the statistical properties of the flares. Based on a previous work on single flares, we consider two families of models: pure synchrotron models and synchrotron self-Compton (SSC) models. We investigate the effect of fluctuations in some relevant parameters (e.g. acceleration properties, density, magnetic field) on the flux distributions. The distribution of these parameters is readily derived from the flux distributions observed at different wavelengths.In both scenarios, we find that fluctuations of the power injected in accelerated particles plays a major role. This must be distributed as a power-law (with different indices in each model). In the synchrotron dominated scenario, we derive the most extreme values of the acceleration power required to reproduce the brightest flares. In that model, the distribution of the acceleration slope fluctuations is constrained and in the SSC scenario we constrain the distributions of the correlated magnetic field and flow density variations.

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Persistent Asymmetric Structure of Sagittarius A* on Event Horizon Scales

Cited by 78 publications

References 73 publications

The Milky Way’s Supermassive Black Hole: How Good a Case Is It?

The Milky Way’s Supermassive Black Hole: How Good a Case Is It?

The Effects of Accretion Flow Dynamics on the Black Hole Shadow of Sagittarius A*

Using infrared/X-ray flare statistics to probe the emission regions near the event horizon of Sgr A*

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