Variable Infrared Emission from the Supermassive Black Hole at the Center of the Milky Way

Ghez, A. M.; Wright, Shelley A.; Matthews, K.; Thompson, D.J.; Mignant, D. Le; Tanner, Angelle; Hornstein, S. D.; Morris, Mark; Becklin, E. E.; Soifer, B. T.

doi:10.1086/382024

Cited by 271 publications

(359 citation statements)

References 31 publications

(48 reference statements)

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“…Its spectral energy distribution (SED) shows an inverted spectrum from the radio to the (sub-)millimeter domain (Falcke et al 2000). It displays order-of-magnitude flares in the infrared and X-ray domain (Baganoff et al 2001;Genzel et al 2003;Eckart et al 2004Eckart et al , 2006aGhez et al 2004). Baganoff et al (2003) detected a very low quiescent X-ray luminosity.…”

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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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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“…However, there is no clear agreement on the precise distribution shape. Analysing data between 2004, Dodds-Eden et al (2010 used a two-component distribution to model the data, with a log-normal population of low flux flares and a power-law distribution with index Γ = −2.7 ± 0.14 at higher fluxes. In contrast, Witzel et al (2012), analysed data between 2003 and 2010 with a different reduction method and found a single power-law distribution with index Γ = −4.2 ± 0.1 at all fluxes 1 .…”

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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“…In the simulation of cases B and C, we find that the duration and the interval between the successive eruptive mass-outflows roughly are in agreement with the flares of Sgr A*. But, the small modulations of luminosity does not correspond to the large amplitudes of the flare intensities observed at various wavelengths, because the amplitudes at radio, IR and X-ray are roughly varied by factors of 1/2, 1-5 and 45, respectively (Genzel et al 2003;Ghez et al 2004;Eckart et al 2006;Meyer et al 2006a,b;Trippe et al 2007;Yusef-Zadeh et al 2009, 2011. It is well known that the submilimeter flare lags the X-ray flare roughly by two hours.…”

Section: A Possible Model To the Flares Of Sgr A*mentioning

confidence: 66%

Unstable mass-outflows in geometrically thick accretion flows around black holes

Okuda¹,

Das

2015

Mon. Not. R. Astron. Soc.

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Accretion flows around black holes generally result in mass-outflows that exhibit irregular behavior quite often. Using 2D time-dependent hydrodynamical calculations, we show that the mass-outflow is unstable in the cases of thick accretion flows such as the low angular momentum accretion flow and the advection-dominated accretion flow. For the low angular momentum flow, the inward accreting matter on the equatorial plane interacts with the outflowing gas along the rotational axis and the centrifugally supported oblique shock is formed at the interface of both the flows, when the viscosity parameter α is as small as α 10 −3 . The hot and rarefied blobs, which result in the eruptive mass-outflow, are generated in the inner shocked region and grow up toward the outer boundary. The advection-dominated accretion flow attains finally in the form of a torus disc with the inner edge of the disc at 3R g r 6R g and the center at 6R g r 10R g , and a series of hot blobs is intermittently formed near the inner edge of the torus and grows up along the outer surface of the torus. As a result, the luminosity and the mass-outflow rate are modulated irregularly where the luminosity is enhanced by 10−40% and the mass-outflow rate is increaed by a factor of few up to ten. We interpret the unstable nature of the outflow to be due to the KelvinHelmholtz instability, examining the Richardson number for the Kelvin-Helmholtz criterion in the inner region of the flow. We propose that the flare phenomena of Sgr A* may be induced by the unstable mass-outflow as is found in this work.

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Variable Infrared Emission from the Supermassive Black Hole at the Center of the Milky Way

Cited by 271 publications

References 31 publications

Millimeter to X-ray flares from Sagittarius A*

Millimeter to X-ray flares from Sagittarius A*

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

Unstable mass-outflows in geometrically thick accretion flows around black holes

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