scholarly journals Status of GRMHD simulations and radiative models of Sgr A*

2016 ◽  
Vol 11 (S322) ◽  
pp. 43-49
Author(s):  
Monika Mościbrodzka
Keyword(s):  
Black Hole ◽  
Galactic Center ◽  
Kerr Black Hole ◽  
Theoretical Models ◽  
Radiative Properties ◽  
X Ray ◽  
Accretion Flows ◽  
General Relativistic ◽  
Sgr A ◽  
Magnetohydrodynamic Simulations

AbstractThe Galactic center is a perfect laboratory for testing various theoretical models of accretion flows onto a supermassive black hole. Here, I review general relativistic magnetohydrodynamic simulations that were used to model emission from the central object - Sgr A*. These models predict dynamical and radiative properties of hot, magnetized, thick accretion disks with jets around a Kerr black hole. Models are compared to radio-VLBI, mm-VLBI, NIR, and X-ray observations of Sgr A*. I present the recent constrains on the free parameters of the model such as accretion rate onto the black hole, the black hole angular momentum, and orientation of the system with respect to our line of sight.

scholarly journals Statistical and theoretical studies of flares from Sagittarius A⋆

2016 ◽  
Vol 11 (S322) ◽  
pp. 31-38
Author(s):  
Ya-Ping Li ◽  
Qiang Yuan ◽  
Q. Daniel Wang ◽  
P. F. Chen ◽  
Joseph Neilsen ◽  
...  
Keyword(s):  
Black Hole ◽  
Solar Flares ◽  
Galactic Center ◽  
Theoretical Models ◽  
Spatial Dimension ◽  
X Ray ◽  
Sagittarius A ◽  
Multi Wavelength ◽  
Self Organized Criticality ◽  
Sgr A

AbstractMulti-wavelength flares have routinely been observed from the supermassive black hole, Sagittarius A⋆ (Sgr A⋆), at our Galactic center. The nature of these flares remains largely unclear, despite many theoretical models. We study the statistical properties of the Sgr A⋆ X-ray flares and find that they are consistent with the theoretical prediction of the self-organized criticality system with the spatial dimension S = 3. We suggest that the X-ray flares represent plasmoid ejections driven by magnetic reconnection (similar to solar flares) in the accretion flow onto the black hole. Motivated by the statistical results, we further develop a time-dependent magnetohydrodynamic (MHD) model for the multi-band flares from Sgr A⋆ by analogy with models of solar flares/coronal mass ejections (CMEs). We calculate the X-ray, infrared flare light curves, and the spectra, and find that our model can explain the main features of the flares.

scholarly journals Relative depolarization of the black hole photon ring in GRMHD models of Sgr A* and M87*

2021 ◽  
Vol 503 (3) ◽  
pp. 4563-4575
Author(s):  
A Jiménez-Rosales ◽  
J Dexter ◽  
S M Ressler ◽  
A Tchekhovskoy ◽  
M Bauböck ◽  
...  
Keyword(s):  
Black Hole ◽  
Relativistic Effects ◽  
Image Features ◽  
Black Hole Mass ◽  
Magnetic Turbulence ◽  
Intensity Images ◽  
General Relativistic ◽  
Sharp Image ◽  
Sgr A ◽  
Magnetohydrodynamic Simulations

ABSTRACT Using general relativistic magnetohydrodynamic simulations of accreting black holes, we show that a suitable subtraction of the linear polarization per pixel from total intensity images can enhance the photon ring feature. We find that the photon ring is typically a factor of ≃2 less polarized than the rest of the image. This is due to a combination of plasma and general relativistic effects, as well as magnetic turbulence. When there are no other persistently depolarized image features, adding the subtracted residuals over time results in a sharp image of the photon ring. We show that the method works well for sample, viable GRMHD models of Sgr A* and M87*, where measurements of the photon ring properties would provide new measurements of black hole mass and spin, and potentially allow for tests of the ‘no-hair’ theorem of general relativity.

scholarly journals Looking for the underlying cause of black hole X-ray variability in GRMHD simulations

2020 ◽  
Vol 496 (3) ◽  
pp. 3808-3828
Author(s):  
D A Bollimpalli ◽  
R Mahmoud ◽  
C Done ◽  
P C Fragile ◽  
W Kluźniak ◽  
...  
Keyword(s):  
Black Hole ◽  
Power Spectra ◽  
Time Lags ◽  
X Ray ◽  
Accretion Flows ◽  
Mass Fluxes ◽  
Frequency Independent ◽  
Show Evidence ◽  
General Relativistic ◽  
Characteristic Features

ABSTRACT Long-term observations have shown that black hole X-ray binaries exhibit strong, aperiodic variability on time-scales of a few milliseconds to seconds. The observed light curves display various characteristic features like a lognormal distribution of flux and a linear rms–flux relation, which indicate that the underlying variability process is stochastic in nature. It is also thought to be intrinsic to accretion. This variability has been modelled as inward propagating fluctuations of mass accretion rate, although the physical process driving the fluctuations remains puzzling. In this work, we analyse five exceptionally long-duration general relativistic magnetohydrodynamic (GRMHD) simulations of optically thin, geometrically thick, black hole accretion flows to look for hints of propagating fluctuations in the simulation data. We find that the accretion profiles from these simulations do show evidence for inward propagating fluctuations below the viscous frequency by featuring strong radial coherence and positive time lags when comparing smaller to larger radii, although these time lags are generally shorter than the viscous time-scale and are frequency-independent. Our simulations also support the notion that the fluctuations in $\dot{M}$ build up in a multiplicative manner, as the simulations exhibit linear rms–mass flux relations, as well as lognormal distributions of their mass fluxes. When combining the mass fluxes from the simulations with an assumed emissivity profile, we additionally find broad agreement with observed power spectra and time lags, including a recovery of the frequency dependency of the time lags.

scholarly journals Pinpointing the base of the AGN jets through general relativistic X-ray reverberation studies

2014 ◽  
Vol 10 (S313) ◽  
pp. 346-351
Author(s):  
D. Emmanoulopoulos
Keyword(s):  
Black Hole ◽  
Time Lag ◽  
Galactic Nuclei ◽  
Theoretical Models ◽  
Significant Information ◽  
Response Models ◽  
X Ray ◽  
Geometrical Properties ◽  
General Relativistic ◽  
Frame Work

AbstractMany theoretical models of Active Galactic Nuclei (AGN) predict that the X-ray corona, lying above the black hole, constitutes the base of the X-ray jet. Thus, by studying the exact geometry of the close black hole environment, we can pinpoint the launching site of the jet. Detection of negative X-ray reverberation time delays (i.e. soft band X-ray variations lagging behind the corresponding hard band X-ray variations) can yield significant information about the geometrical properties of the AGN, such as the location of the X-ray source, as well as the physical properties of the the black hole, such as its mass and spin. In the frame-work of the lamp-post geometry, I present the first systematic X-ray time-lag modelling results of an ensemble of 12 AGN, using a fully general relativistic (GR) ray tracing approach for the estimation of the systems' response functions. By combing these state-of-the art GR response models with statistically innovative fitting routines, I derive the geometrical layout of the close BH environment for each source, unveiling the position of the AGN jet-base.

scholarly journals How to tell an accreting boson star from a black hole

2020 ◽  
Vol 497 (1) ◽  
pp. 521-535 ◽  
Author(s):  
Hector Olivares ◽  
Ziri Younsi ◽  
Christian M Fromm ◽  
Mariafelicia De Laurentis ◽  
Oliver Porth ◽  
...  
Keyword(s):  
Black Hole ◽  
Radiative Transfer ◽  
Event Horizon ◽  
Polar Regions ◽  
Radio Observations ◽  
Accretion Flow ◽  
Supermassive Black Hole ◽  
General Relativistic ◽  
Sgr A ◽  
Magnetohydrodynamic Simulations

ABSTRACT The capability of the Event Horizon Telescope (EHT) to image the nearest supermassive black hole candidates at horizon-scale resolutions offers a novel means to study gravity in its strongest regimes and to test different models for these objects. Here, we study the observational appearance at 230 GHz of a surfaceless black hole mimicker, namely a non-rotating boson star, in a scenario consistent with the properties of the accretion flow on to Sgr A*. To this end, we perform general relativistic magnetohydrodynamic simulations followed by general relativistic radiative transfer calculations in the boson star space–time. Synthetic reconstructed images considering realistic astronomical observing conditions show that, despite qualitative similarities, the differences in the appearance of a black hole – either rotating or not – and a boson star of the type considered here are large enough to be detectable. These differences arise from dynamical effects directly related to the absence of an event horizon, in particular, the accumulation of matter in the form of a small torus or a spheroidal cloud in the interior of the boson star, and the absence of an evacuated high-magnetization funnel in the polar regions. The mechanism behind these effects is general enough to apply to other horizonless and surfaceless black hole mimickers, strengthening confidence in the ability of the EHT to identify such objects via radio observations.

scholarly journals Extraction of Black Hole Rotational Energy by a Magnetic Field

2003 ◽  
Vol 214 ◽  
pp. 87-90
Author(s):  
Shinji Koide
Keyword(s):  
Magnetic Field ◽  
Black Hole ◽  
Large Scale ◽  
Kerr Black Hole ◽  
Negative Energy ◽  
Rotational Energy ◽  
Alfven Wave ◽  
Numerical Result ◽  
General Relativistic ◽  
Magnetohydrodynamic Simulations

We have developed a numerical method for general relativistic magnetohydrodynamic simulations in Kerr space-time. The method is applied to the basic astrophysical problem of the Kerr black hole activity in the large-scale strong magnetic field. The numerical result shows that the magnetic field extracts the rotational energy of the black hole with negative energy-at-infinity and the torsional Alfven wave is induced from the ergosphere.

scholarly journals General relativistic MHD simulations of non-thermal flaring in Sagittarius A*

2021 ◽  
Author(s):  
K Chatterjee ◽  
S Markoff ◽  
J Neilsen ◽  
Z Younsi ◽  
G Witzel ◽  
...  
Keyword(s):  
Particle Acceleration ◽  
Near Infrared ◽  
Power Spectra ◽  
X Rays ◽  
Thermal Electron ◽  
X Ray ◽  
Particle Distributions ◽  
Accretion Flows ◽  
General Relativistic ◽  
Sgr A

Abstract Sgr A* exhibits regular variability in its multiwavelength emission, including daily X-ray flares and roughly continuous near-infrared (NIR) flickering. The origin of this variability is still ambiguous since both inverse Compton and synchrotron emission are possible radiative mechanisms. The underlying particle distributions are also not well constrained, particularly the non-thermal contribution. In this work, we employ the GPU-accelerated general relativistic magnetohydrodynamics (GRMHD) code H-AMR to perform a study of flare flux distributions, including the effect of particle acceleration for the first time in high-resolution 3D simulations of Sgr A*. For the particle acceleration, we use the general relativistic ray-tracing (GRRT) code BHOSS to perform the radiative transfer, assuming a hybrid thermal+non-thermal electron energy distribution. We extract ∼60 hr lightcurves in the sub-millimetre, NIR and X-ray wavebands, and compare the power spectra and the cumulative flux distributions of the lightcurves to statistical descriptions for Sgr A* flares. Our results indicate that non-thermal populations of electrons arising from turbulence-driven reconnection in weakly magnetised accretion flows lead to moderate NIR and X-ray flares and reasonably describe the X-ray flux distribution while fulfilling multiwavelength flux constraints. These models exhibit high rms per cent amplitudes, $\gtrsim 150{{\ \rm per\ cent}}$ both in the NIR and the X-rays, with changes in the accretion rate driving the 230 GHz flux variability, in agreement with Sgr A* observations.

scholarly journals Living on the edge: Rossby wave instability and HFQPOs in black hole binaries

2020 ◽  
Vol 638 ◽  
pp. A33 ◽  
Author(s):  
P. Varniere ◽  
F. H. Vincent ◽  
F. Casse
Keyword(s):  
Black Hole ◽  
Rossby Wave ◽  
Kerr Black Hole ◽  
High Energy ◽  
Accretion Disc ◽  
Wave Instability ◽  
Stable Orbit ◽  
X Ray ◽  
General Relativistic ◽  
The Impact

Context. The Rossby wave instability (RWI) has been proposed to explain the origin of the high-frequency quasi-periodic oscillations observed in the X-ray emission of astrophysical systems harbouring black holes. Recent numerical computations have proven that the RWI does exist in a general relativistic context and that its presence is associated with a time-variable X-ray emission from the disc. Aims. Using our new Numerical Observatory of Violent Accreting system, NOVAs, we explore the way the RWI impacts an accretion disc orbiting a spinning black hole under realistic astrophysical conditions. Our aim is to study the impact of the presence of the RWI in the very inner part of the accretion disc on known observables and explore some possibly new ones. Methods. We present the first full general relativistic hydrodynamical simulations of the RWI occurring at the last stable orbit of an accretion disc orbiting around a Kerr black-hole. Those simulations, coupled with a full general relativistic ray-tracing, have allowed us to directly compare our simulations with the observables we obtained from the X-ray emission of the disc. Results. Our study shows, for the first time, that the RWI naturally arises near the inner edge of an accretion disc whenever it gets close to its last stable orbit, as predicted analytically. From there, we show that not only does the RWI create a visible timing feature but it also impacts the energy spectrum of the source, which exhibits a high energy extension due to the presence of hot vortices generated by the RWI in the disc. Our study also shows that systems with the RWI present at the inner edge of the disc only exhibit similar behavior to systems in which HFQPOs have been detected.

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