PROSPECTS FOR TESTING THE NATURE OF Sgr A*'s NEAR-INFRARED FLARES ON THE BASIS OF CURRENT VERY LARGE TELESCOPE—AND FUTURE VERY LARGE TELESCOPE INTERFEROMETER—OBSERVATIONS

Hamaus, Nico; Paumard, T.; Müller, Thomas; Gillessen, S.; Eisenhauer, F.; Trippe, Sascha; Genzel, R.

doi:10.1088/0004-637x/692/1/902

Cited by 69 publications

(90 citation statements)

References 67 publications

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“…Such applications would provide valuable counterparts to potential astrometry of the flaring region with polarimetric VLBI or with near-infrared interferometry (e.g., Hamaus et al 2009;Vincent et al 2011). Our method may also be valuable for other observations of time-variable structures with sparse visibility data.…”

Section: Discussionmentioning

confidence: 99%

Measuring the Direction and Angular Velocity of a Black Hole Accretion Disk via Lagged Interferometric Covariance

Johnson

Loeb

Shiokawa

et al. 2015

ApJ

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We show that interferometry can be applied to study irregular, rapidly rotating structures, as are expected in the turbulent accretion flow near a black hole. Specifically, we analyze the lagged covariance between interferometric baselines of similar lengths but slightly different orientations. For a flow viewed close to face-on, we demonstrate that the peak in the lagged covariance indicates the direction and angular velocity of the emission pattern from the flow. Even for moderately inclined flows, the covariance robustly estimates the flow direction, although the estimated angular velocity can be significantly biased. Importantly, measuring the direction of the flow as clockwise or counterclockwise on the sky breaks a degeneracy in accretion disk inclinations when analyzing timeaveraged images alone. We explore the potential efficacy of our technique using three-dimensional, general relativistic magnetohydrodynamic simulations, and we highlight several baseline pairs for the Event Horizon Telescope (EHT) that are well-suited to this application. These results indicate that the EHT may be capable of estimating the direction and angular velocity of the emitting material near Sgr A * , and they suggest that a rotating flow may even be utilized to improve imaging capabilities.

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Section: Discussionmentioning

confidence: 99%

Measuring the Direction and Angular Velocity of a Black Hole Accretion Disk via Lagged Interferometric Covariance

Johnson

Loeb

Shiokawa

et al. 2015

ApJ

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“…Indeed in the hotspot model, the combined effects of the beaming and the gravitational redshift on the proper luminosity are small at r = 100 r g since the corresponding orbital period is ∼1.5 days, which implies that any magnification has a long timescale and a very small amplitude (Broderick & Loeb 2005;Hamaus et al 2009). In the jet geometry, the Doppler factor is small owing to the small inclination and the mild velocity of the Sgr A* jet; therefore, the beaming factor, varying as the square of the Doppler factor, is also small (Barrière et al 2014).…”

Section: Magnetic Energy Heatingmentioning

confidence: 99%

Study of the X-ray activity of Sagittarius A* during the 2011XMM-Newtoncampaign

Mossoux

Grosso

Vincent

et al. 2014

A&A

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Context. At the dynamical center of the Milky Way, there is the closest supermassive black hole: Sgr A*. Its non-flaring luminosity is several orders of magnitude lower than the Eddington luminosity, but flares can be observed in the infrared and X-rays. This flaring activity can help us to understand radiation mechanisms from Sgr A*. Aims. Our aim is to investigate the X-ray flaring activity of Sgr A* and to constrain the physical properties of the X-ray flares and their origin. Methods. In March and April 2011, we observed Sgr A* with XMM-Newton with a total exposure of ≈ 226 ks in coordination with the 1.3 mm Very-Long-Baseline Interferometry array. We performed timing analysis of the X-ray emission from Sgr A* using a Bayesian-blocks algorithm to detect X-ray flares observed with XMM-Newton. Furthermore, we computed X-ray smoothed light curves observed in this campaign in order to have better accuracy on the position and the amplitude of the flares. Results. We detected two X-ray flares on March 30 and April 3, 2011, which for comparison have a peak detection level of 6.8 and 5.9 σ in the XMM-Newton/EPIC (pn+MOS1+MOS2) light curve in the 2−10 keV energy range with a 300 s bin. The former is characterized by two sub-flares: the first one is very short (∼ 458 s) with a peak luminosity of L unabs 2−10 keV ∼ 9.4 × 10 34 erg s −1 , whereas the second one is longer (∼ 1542 s) with a lower peak luminosity (L unabs 2−10 keV ∼ 6.8 × 10 34 erg s −1 ). The comparison with the sample of X-ray flares detected during the 2012 Chandra XVP campaign favors the hypothesis that the 2011 March 30 flare is a single flare rather than two distinct subflares. We model the light curve of this flare with the gravitational lensing of a simple hotspot-like structure, but we cannot satisfactorily reproduce the large decay of the light curve between the two subflares with this model. From magnetic energy heating during the rise phase of the first subflare and assuming an X-ray photons production efficiency of 1 and a magnetic field of 100 G at 2 r g , we derive an upper limit to the radial distance of the first subflare of 100 +19 −29 r g . We use the decay phase of the first subflare to estimate a lower limit to the radial distance of 4 r g from synchrotron cooling in the infrared. Conclusions. The X-ray emitting region of the first subflare is located at a radial position of 4 − 100 +19−29 and has a corresponding radius of 1.8 − 2.87 ± 0.01 in r g unit for a magnetic field of 100 G at 2 r g .

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“…Doing transformative science will require connecting accretion and jet physics and signatures of strong gravity to the non-imaging interferometric (closure phase and polarized visibilities, e.g., see Figure 1) and astrometric observables. These observables have been calculated from orbiting hotspot models (Hamaus et al 2009;Doeleman et al 2009;Fish et al 2009), but should be explored using numerical simulations where the dynamics is treated self-consistently. It will also be important to leverage all existing observational constraints, e.g.…”

Section: Discussionmentioning

confidence: 99%

“…The predicted "shadow" (Bardeen 1973;Falcke et al 2000) may be detected by future EHT observations. Time-resolved astrometry with VLTI GRAVITY data could map out particle orbits near the event horizon (Hamaus et al 2009). …”

Section: Introductionmentioning

confidence: 99%

Event horizon scale emission models for Sagittarius A*

Dexter¹

2013

Proc. IAU

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Abstract. Very long baseline interferometry observations at millimeter wavelengths have detected source structure in Sgr A* on event horizon scales. Near-infrared interferometry will achieve similar resolution in the next few years. These experiments provide an unprecedented opportunity to explore strong gravity around black holes, but interpreting the data requires physical modeling. I discuss the calculation of images, spectra, and light curves from relativistic MHD simulations of black hole accretion. The models provide an excellent description of current observations, and predict that we may be on the verge of detecting a black hole shadow, which would constitute the first direct evidence for the existence of black holes.

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PROSPECTS FOR TESTING THE NATURE OF Sgr A*'s NEAR-INFRARED FLARES ON THE BASIS OF CURRENT VERY LARGE TELESCOPE—AND FUTURE VERY LARGE TELESCOPE INTERFEROMETER—OBSERVATIONS

Cited by 69 publications

References 67 publications

Measuring the Direction and Angular Velocity of a Black Hole Accretion Disk via Lagged Interferometric Covariance

Measuring the Direction and Angular Velocity of a Black Hole Accretion Disk via Lagged Interferometric Covariance

Study of the X-ray activity of Sagittarius A* during the 2011XMM-Newtoncampaign

Event horizon scale emission models for Sagittarius A*

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