scholarly journals HFQPOs and discoseismic mode excitation in eccentric, relativistic discs. II. Magnetohydrodynamic simulations

2020 ◽  
Vol 497 (1) ◽  
pp. 451-465 ◽  
Author(s):  
Janosz W Dewberry ◽  
Henrik N Latter ◽  
Gordon I Ogilvie ◽  
Sebastien Fromang
Keyword(s):  
Binary Systems ◽  
Wave Excitation ◽  
Mhd Turbulence ◽  
Magnetorotational Instability ◽  
X Ray ◽  
Mhd Simulations ◽  
The Face ◽  
Inertial Wave ◽  
Net Flux ◽  
Magnetohydrodynamic Simulations

ABSTRACT Trapped inertial oscillations (r modes) provide a promising explanation for high-frequency quasi-periodic oscillations (HFQPOs) observed in the emission from black hole X-ray binary systems. An eccentricity (or warp) can excite r modes to large amplitudes, but concurrently, the oscillations are likely damped by magnetohydrodynamic (MHD) turbulence driven by the magnetorotational instability (MRI). We force eccentricity in global, unstratified, zero-net-flux MHD simulations of relativistic accretion discs and find that a sufficiently strong disc distortion generates trapped inertial waves despite this damping. In our simulations, eccentricities above ∼0.03 in the inner disc excite trapped waves. In addition to the competition between r-mode damping and driving, we observe that larger amplitude eccentric structures modify and in some cases suppress MRI turbulence. Given the variety of distortions (warps as well as eccentricities) capable of amplifying r modes, the robustness of trapped inertial wave excitation in the face of MRI turbulence in our simulations provides support for a discoseismic explanation for HFQPOs.

scholarly journals Wave modes from the magnetorotational instability in accretion discs

2012 ◽  
Vol 8 (S290) ◽  
pp. 201-202
Author(s):  
Giuseppe Di Bernardo ◽  
Ulf Torkelsson
Keyword(s):  
Three Dimensional ◽  
Accretion Disc ◽  
Light Curves ◽  
Accretion Discs ◽  
Magnetorotational Instability ◽  
Periodic Oscillations ◽  
X Ray ◽  
Black Hole Binaries ◽  
Angular Momentum Transport ◽  
Magnetohydrodynamic Simulations

AbstractThe magnetorotational instability (MRI) is widely believed to be the source of turbulence in accretion discs. This turbulence is responsible for the anomalous angular momentum transport in accretion discs. The turbulence will affect other aspects of the dynamics of the disc as well, and we will concentrate on two such issues: a) what kind of oscillations can be excited by the turbulence itself, and b) how the turbulence is interacting with modes that have been excited by some other agent. This is of interest in understanding the quasi-periodic oscillations (QPOs) that have been observed in the X-ray light curves of accreting neutron star and black hole binaries. We carry out local three dimensional (3D) magnetohydrodynamic simulations of a keplerian differentially rotating accretion disc, using a shearing box configuration taking in account the effects of the vertical stratification.

scholarly journals MHD simulations of the magnetorotational instability in a shearing box with zero net flux

2007 ◽  
Vol 476 (3) ◽  
pp. 1123-1132 ◽  
Author(s):  
S. Fromang ◽  
J. Papaloizou ◽  
G. Lesur ◽  
T. Heinemann
Keyword(s):  
Magnetorotational Instability ◽  
Mhd Simulations ◽  
Net Flux

scholarly journals Magnetohydrodynamic simulations of the collapsar model for early and late evolution of gamma-ray bursts

2007 ◽  
Vol 365 (1854) ◽  
pp. 1207-1212
Author(s):  
Daniel Proga
Keyword(s):  
Gamma Ray ◽  
Gamma Ray Bursts ◽  
Energy Output ◽  
Time Behaviour ◽  
Supply Rate ◽  
X Ray ◽  
Mhd Simulations ◽  
Late Evolution ◽  
Magnetohydrodynamic Simulations ◽  
Gaseous Envelope

I present results from magnetohydrodynamic (MHD) simulations of a gaseous envelope collapsing onto a black hole (BH). These results support the notion that the collapsar model is one of the most promising scenarios to explain the huge release of energy in a matter of seconds associated with gamma-ray bursts (GRBs). Additionally, the MHD simulations show that at late times, when the mass supply rate is expected to decrease, the region in the vicinity of the BH can play an important role in determining the rate of accretion, its time behaviour and ultimately the energy output. In particular, the magnetic flux accumulated around the BH can repeatedly stop and then restart the energy release. As proposed by Proga & Zhang, the episode or episodes of reoccurrence of accretion processes can correspond to X-ray flares discovered recently in a number of GRBs.

scholarly journals HFQPOs and discoseismic mode excitation in eccentric, relativistic discs. I. Hydrodynamic simulations

2020 ◽  
Vol 497 (1) ◽  
pp. 435-450 ◽  
Author(s):  
Janosz W Dewberry ◽  
Henrik N Latter ◽  
Gordon I Ogilvie ◽  
Sebastien Fromang
Keyword(s):  
Black Hole ◽  
Binary Systems ◽  
Companion Paper ◽  
Inertial Waves ◽  
Magnetorotational Instability ◽  
Hydrodynamic Simulations ◽  
Stable Circular Orbit ◽  
Innermost Stable Circular Orbit ◽  
Inertial Wave ◽  
First Time

ABSTRACT High-frequency quasi-periodic oscillations (HFQPOs) observed in the emission of black hole X-ray binary systems promise insight into strongly curved spacetime. ‘Discoseismic’ oscillations with frequencies set by the intrinsic properties of the central black hole, in particular ‘trapped inertial waves’ (r modes), offer an attractive explanation for HFQPOs. To produce an observable signature, however, such oscillations must be excited to sufficiently large amplitudes. Turbulence driven by the magnetorotational instability fails to provide the necessary amplification, but r modes may still be excited via interaction with accretion disc warps or eccentricities. We present 3D global hydrodynamic simulations of relativistic accretion discs, which demonstrate for the first time the excitation of trapped inertial waves by an imposed eccentricity in the flow. While the r modes’ saturated state depends on the vertical boundary conditions used in our unstratified, cylindrical framework, their excitation is unambiguous in all runs with eccentricity ≳ 0.005 near the innermost stable circular orbit. These simulations provide a proof of concept, demonstrating the robustness of trapped inertial wave excitation in a non-magnetized context. In a companion paper, we explore the competition between this excitation, and damping by magnetohydrodynamic turbulence.

scholarly journals Magnetohydrodynamics in a cylindrical shearing box

2019 ◽  
Vol 71 (5) ◽  
Author(s):  
Takeru K Suzuki ◽  
Tetsuo Taki ◽  
Scott S Suriano
Keyword(s):  
Mhd Equations ◽  
Radial Dependence ◽  
Mhd Turbulence ◽  
Magnetorotational Instability ◽  
Mhd Simulations ◽  
Self Consistent ◽  
Consistent Manner ◽  
Set Up ◽  
Isothermal Equation ◽  
Physical Quantities

ABSTRACT We develop a framework for magnetohydrodynamical (MHD) simulations in a local cylindrical shearing box by extending the formulation of the Cartesian shearing box. We construct shearing-periodic conditions at the radial boundaries of a simulation box from the conservation relations of the basic MHD equations, taking into account the explicit radial dependence of physical quantities. We demonstrate quasi-steady mass accretion, which cannot be handled by the standard Cartesian shearing box model, with an ideal MHD simulation in a vertically unstratified cylindrical shearing box for up to 200 rotations. In this demonstrative run we set up (i) net vertical magnetic flux, (ii) a locally isothermal equation of state, and (iii) a sub-Keplerian equilibrium rotation, whereas the sound velocity and the initial Alfvén velocity have the same radial dependence as that of the Keplerian velocity. Inward mass accretion is induced to balance the outward angular momentum flux of the MHD turbulence triggered by the magnetorotational instability in a self-consistent manner. We discuss detailed physical properties of the saturated magnetic field, in comparison to the results of a Cartesian shearing box simulation.

scholarly journals Recent results from simulations of the magnetorotational instability

2010 ◽  
Vol 6 (S274) ◽  
pp. 422-428 ◽  
Author(s):  
James M. Stone
Keyword(s):  
Particle Acceleration ◽  
First Principles ◽  
Mhd Turbulence ◽  
Magnetorotational Instability ◽  
Nonlinear Saturation ◽  
Global Models ◽  
Mhd Simulations ◽  
Control Saturation ◽  
Future Work ◽  
Local Shearing

AbstractThe nonlinear saturation of the magnetorotational instability (MRI) is best studied through numerical MHD simulations. Recent results of simulations that adopt the local shearing box approximation, and fully global models that follow the entire disk, are described. Outstanding issues remain, such as a first-principles understanding of the dynamo processes that control saturation with no net magnetic flux. Important directions for future work include a better understanding of basic plasma processes, such as reconnection, dissipation, and particle acceleration, in the MHD turbulence driven by the MRI.

Fractionation of polymethylene chains: An electron crystallographic investigation

1986 ◽  
Vol 44 ◽  
pp. 794-795
Author(s):  
Douglas L. Dorset
Keyword(s):  
Cross Section ◽  
Binary Systems ◽  
Linear Chain ◽  
Pure Component ◽  
Organic Substrates ◽  
Crystallographic Investigation ◽  
X Ray Diffraction ◽  
X Ray ◽  
Molecular Sizes ◽  
The Stability

A variety of linear chain materials exist as polydisperse systems which are difficultly purified. The stability of continuous binary solid solutions assume that the Gibbs free energy of the solution is lower than that of either crystal component, a condition which includes such factors as relative molecular sizes and shapes and perhaps the symmetry of the pure component crystal structures.Although extensive studies of n-alkane miscibility have been carried out via powder X-ray diffraction of bulk samples we have begun to examine binary systems as single crystals, taking advantage of the well-known enhanced scattering cross section of matter for electrons and also the favorable projection of a paraffin crystal structure posited by epitaxial crystallization of such samples on organic substrates such as benzoic acid.

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