A<i>CHANDRA</i>/HETGS CENSUS OF X-RAY VARIABILITY FROM Sgr A* DURING 2012

Neilsen, Joseph; Nowak, Michael A.; Gammie, Charles F.; Dexter, Jason; Markoff, Sera; Haggard, Daryl; Nayakshin, Sergei; Wang, Q. Daniel; Grosso, N.; Porquet, D.; Tomsick, John A.; Degenaar, N.; Fragile, P. Chris; Houck, J. C.; Wijnands, Rudy; Miller, J. M.; Baganoff, Frederick K.

doi:10.1088/0004-637x/774/1/42

Cited by 182 publications

(350 citation statements)

References 93 publications

(137 reference statements)

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“…We found, however, that our results depended very strongly on the assumed power-law indices of the density and temperature profiles as well as on the choice of the point at which the extrapolation matched the numerical solutions. Instead of following this approach, we opt to use the result of Shcherbakov & Baganoff (2010, see also the discussion in Neilsen et al 2013) that 10% of the quiescent X-ray flux from Sgr A* originates in a point source and attribute 10% of the observed flux to the emission from our simulated volume.…”

Section: Current Spectral and Imagingmentioning

confidence: 99%

THE POWER OF IMAGING: CONSTRAINING THE PLASMA PROPERTIES OF GRMHD SIMULATIONS USING EHT OBSERVATIONS OF Sgr A*

Chan

Psaltis

Özel

et al. 2015

ApJ

139

162

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Recent advances in general relativistic magnetohydrodynamic simulations have expanded and improved our understanding of the dynamics of black-hole accretion disks. However, current simulations do not capture the thermodynamics of electrons in the low density accreting plasma. This poses a significant challenge in predicting accretion flow images and spectra from first principles. Because of this, simplified emission models have often been used, with widely different configurations (e.g., disk-versus jet-dominated emission), and were able to account for the observed spectral properties of accreting black holes. Exploring the large parameter space introduced by such models, however, requires significant computational power that exceeds conventional computational facilities. In this paper, we use GRay, a fast graphics processing unit (GPU) based ray-tracing algorithm, on the GPU cluster El Gato, to compute images and spectra for a set of six general relativistic magnetohydrodynamic simulations with different magnetic field configurations and black-hole spins. We also employ two different parametric models for the plasma thermodynamics in each of the simulations. We show that, if only the spectral properties of Sgr A * are used, all 12 models tested here can fit the spectra equally well. However, when combined with the measurement of the image size of the emission using the Event Horizon Telescope, current observations rule out all models with strong funnel emission, because the funnels are typically very extended. Our study shows that images of accretion flows with horizon-scale resolution offer a powerful tool in understanding accretion flows around black holes and their thermodynamic properties.

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Section: Current Spectral and Imagingmentioning

confidence: 99%

THE POWER OF IMAGING: CONSTRAINING THE PLASMA PROPERTIES OF GRMHD SIMULATIONS USING EHT OBSERVATIONS OF Sgr A*

Chan

Psaltis

Özel

et al. 2015

ApJ

139

162

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“…This has been done in two ways. Neilsen et al (2013) considered only well resolved individual flares and assumed a common power-law spectral shape. They find that the averaged flare luminosity is distributed as a power-law with index Γ = −1.9 +0.3 −0.4 .…”

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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“…During this campaign we observed 39 new X-ray flares, roughly tripling the number observed and allowing for the first statistical analyses (Nowak et al 2012;Neilsen et al 2013). These X-ray flares seem to always be accompanied by simultaneous NIR flaring, though many NIR flares are seen without corresponding X-ray activity.…”

mentioning

confidence: 99%

The Intrinsic Two-Dimensional Size of Sagittarius A*

Bower

Markoff

Brunthaler

et al. 2014

ApJ

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General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. Download date: 12 May 2018The Astrophysical Journal, 790:1 (10pp), 2014 July 20 doi:10.1088/0004-637X/790/1/1 C 2014. The American Astronomical Society. All rights reserved. Printed in the U.S.A. ABSTRACT We report the detection of the two-dimensional structure of the radio source associated with the Galactic Center black hole, Sagittarius A*, obtained from Very Long Baseline Array observations at a wavelength of 7 mm. The intrinsic source is modeled as an elliptical Gaussian with major-axis size 35.4 × 12.6 R S in position angle 95 THE INTRINSIC TWO-DIMENSIONAL SIZE OF SAGITTARIUS A*• east of north. This morphology can be interpreted in the context of both jet and accretion disk models for the radio emission. There is supporting evidence in large angular-scale multi-wavelength observations for both source models for a preferred axis near 95• . We also place a maximum peak-to-peak change of 15% in the intrinsic major-axis size over five different epochs. Three observations were triggered by detection of near infrared (NIR) flares and one was simultaneous with a large X-ray flare detected by NuSTAR. The absence of simultaneous and quasi-simultaneous flares indicates that not all high energy events produce variability at radio wavelengths. This supports the conclusion that NIR and X-ray flares are primarily due to electron excitation and not to an enhanced accretion rate onto the black hole.

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ACHANDRA/HETGS CENSUS OF X-RAY VARIABILITY FROM Sgr A* DURING 2012

Cited by 182 publications

References 93 publications

THE POWER OF IMAGING: CONSTRAINING THE PLASMA PROPERTIES OF GRMHD SIMULATIONS USING EHT OBSERVATIONS OF Sgr A*

THE POWER OF IMAGING: CONSTRAINING THE PLASMA PROPERTIES OF GRMHD SIMULATIONS USING EHT OBSERVATIONS OF Sgr A*

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

The Intrinsic Two-Dimensional Size of Sagittarius A*

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