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Global 3D MHD Simulations of Optically Thin Black Hole Accretion Disks

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Title: Global 3D MHD Simulations of Optically Thin Black Hole Accretion Disks


1
Global 3D MHD Simulations of Optically Thin Black
Hole Accretion Disks
  • Ryoji Matsumoto?
  • Mami Machida and Kenji Nakamura

2
Time Variabilities of Black Hole Candidates
GRS1915105
X-ray variability of Cyg X-1
3
Conventional Theory of Accretion Disks Introduces
Viscosity Parameter a
  • Standard Accretion Disk Model (Shakura and
    Sunyaev 1973) trf aP
  • a 0.01-0.1 gtgt Molecular Viscosity
  • MRI (Balbus and Hawley 1991) can generate
    magnetic turbulence and enhance the efficiency of
    angular momentum transport

4
We study the time variabilities of black hole
accretion flows by direct global 3D MHD
simulations
5
Basic Equations
6
Global Three-dimensional MHD Simulations of
Black Hole Accretion Flows
(Machida and Matsumoto 2003 ApJ )
Gravitational potential f - GM/(r-rg)
Angular momentum initially uniform at
R50rg Pgas/Pmag ß 100 Magnetic Reynolds
Number Rm 2000, (J/?-vc gt
0)
25064192mesh
2
Anomalous Resistivity ? (1/Rm) max (J/?) /vc
1, 0.0
7
Time Variation of Density Distribution
8
Equatorial Density and Magnetic Field Lines
(rlt60)
(rlt10)
9
Numerical Results Reproduce X-ray variability of
Black Hole Candidates
Numerical Results Time Variation of Accretion
Rate
X-ray Flux from Cyg X-1
10
Comparison of PSD Obtained by Observation and
Numerical Simulation(see Machidas poster)
-0.9
PSD
f
-1.5
f
1Hz
100Hz
frequency
Power Spectral Density (PSD) of Time Variation in
Cyg X-1
PSD of accretion rate obtained by Numerical
Simulation
11
X-ray Shot of Cyg X-1
hard
soft
Negoro et al. 2001
X-ray Intensity Variation in Cyg X-1 (Negoro
1995)
Manmoto et al. 1996
12
Time Variation of the Equatorial Density
3000 rg/c
13
Magnetic Flare in the Innermost Region
Joule Heating
T30590
Current density
Magnetic energy
T30610
Accretion rate
T30630
Current density and magnetic field lines
time
14
(No Transcript)
15
State Transition of Black Hole Accretion Flows
Simulated by Global 3D MHD Simulations including
Radiative Cooling
16
State Transition in Accretion Disks
  • Optically thick, geometrically thin disk
    (high/soft)

X-ray intensity
Qrad Qvis

energy
  • Optically thin disk (low/hard)

X-ray intensity
Qadv Qvis
energy
17
Thermal Equilibrium Curve of Accretion Disks
Abramowicz et al. 1995
Accretion Rate
Slim
ADAF
SADM
Surface Density
Optically thick
Optically thin
18
Correlation between Surface Density and Accretion
Rate in Non-radiative Disk Simulation
Accretion Rate
r 2.5
ADAF Solution
r 5.0
S
19
Numerical Simulation of Transition between Hard
State to Soft State
Abramowicz et al. 1995
Accretion Rate
Slim
ADAF
SADM
Surface Density
Optically thick
Optically thin
20
We Included Optically Thin Radiative Cooling
  • Cooling term is switched on after the accretion
    flow becomes quasi-steady
  • We assume bremsstrahlung cooling
  • Qbrem ? ? T
  • Cooling is not included in rarefied corona where
    ?lt?crit

1/2
2
21
Numerical Result
Hot
Cool
22
Summary of Numerical Results
Cool Down
ADAF
Low ßdisk
Mdot decrease S increase
Mdotdecresase Sdecrease
23
Time Development in SMdot plane
24
During the Transition from Low/hard State to
High/soft state, Mdot Decreases
Abramowicz et al. 1995
Accretion Rate
Slim
ADAF
SADM
Surface Density
Optically thick
Optically thin
25
X-ray Light Curve of GRS1915105
26
Summary
  1. We carried out global 3D MHD simulations of
    radiatively inefficient black hole accretion
    flows without assuming the viscosity parameter a
  2. Numerical results reproduce the time
    variabilities observed in X-ray hard states of
    black hole candidates
  3. State transision from low/hard state to high/soft
    state is simulated by including optically thin
    radiative cooling
  4. Next target is the global simulations of
    radiatively efficient disk
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