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Accretion/Blandford-Znajeck processes and jet formation. Maxim Barkov MPI-K, Heidelberg, Germany Space Research Institute, Russia, University of Leeds, UK Serguei Komissarov University of Leeds, UK. Blandford-Znajek mechanism.

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slide1
Accretion/Blandford-Znajeck processes

and jet formation

Maxim Barkov

MPI-K, Heidelberg, Germany

Space Research Institute, Russia,

University of Leeds, UK

Serguei Komissarov

University of Leeds, UK

Variable Galactic Gamma-Ray Sources , Heidelberg, Germany

slide2
Blandford-Znajek mechanism

In the last few years we can see significant progress in general relativistic magneto hydrodynamics (GRMHD) simulations of BH accretion systems. It reveals a flow structure that can be decomposed into a disk, corona, disk wind and highly magnetized polar region that contains the jet (De Villiers, Hawley and Krolik 2003; Hawley and Krolik 2006; McKinney and Gammie 2004; McKinney 2005, 2006, 2007; McKinney and Balndford 2009; Shibata, Sekiguchi and Takahashi, 2007, Barkov and Komissarov 2008, 2010, Barkov and Baushev 2011).

Variable Galactic Gamma-Ray Sources , Heidelberg, Germany

slide4
III. Numerical simulations

Setup

(Barkov & Komissarov 2008a,b)

(Komissarov & Barkov 2009)

Uniform magnetization

R=4500km

Y= 4x1027-4x1028Gcm-2

black hole

M=3Msun

a=0.9

Rotation:

rc=6.3x103km

l0 = 1017 cm2 s-1

  • 2D axisymmetric
  • GRMHD;
  • Kerr-Schild metric;
  • Realistic EOS;
  • Neutrino cooling;
  • Starts at 1s from
  • collapse onset.
  • Lasts for < 1s

outer boundary,

R= 2.5x104 km

free fall

accretion

(Bethe 1990)

Variable Galactic Gamma-Ray Sources , Heidelberg, Germany

slide5
Free fall model of collapsing star(Bethe, 1990)‏

radial velocity:

mass density:

accretion rate:

Gravity: gravitational field of Black Hole only (Kerr metric);

no self-gravity;

Microphysics: neutrino cooling ;

realistic equation of state, (HELM, Timmes & Swesty, 2000);

dissociation of nuclei (Ardeljan et al., 2005);

Ideal Relativistic MHD - no physical resistivity (only numerical);

Variable Galactic Gamma-Ray Sources , Heidelberg, Germany

slide6
Model:A

C1=9; Bp=3x1010 G

unit length=4.5km

t=0.24s

log10 B/Bp

log10  (g/cm3)

log10 P/Pm

magnetic field lines, and velocity vectors

Variable Galactic Gamma-Ray Sources , Heidelberg, Germany

slide7
Model:A

C1=9; Bp=3x1010 G

unit length=4.5km

t=0.31s

log10  (g/cm3)

magnetic field lines, and velocity vectors

Variable Galactic Gamma-Ray Sources , Heidelberg, Germany

slide8
Model:A

C1=9; Bp=3x1010 G

log10  (g/cm3)

magnetic field lines

Variable Galactic Gamma-Ray Sources , Heidelberg, Germany

slide9
Model:C

C1=3; Bp=1010 G

log10 P/Pm

velocity vectors

Variable Galactic Gamma-Ray Sources , Heidelberg, Germany

slide10
Jets are powered mainly by the black hole via

the Blandford-Znajek mechanism !!

Model: C

  • No explosion if a=0;
  • Jets originate from

the black hole;

  • ~90% of total magnetic flux

is accumulated by the black hole;

  • Energy flux in the ouflow ~

energy flux through the horizon

(disk contribution < 10%);

  • Theoretical BZ power:

Variable Galactic Gamma-Ray Sources , Heidelberg, Germany

slide11
1/50 of case a=0.9

Variable Galactic Gamma-Ray Sources , Heidelberg, Germany

slide14
Different magnetic field topologies:

Dipole, quadruple 1 and quadruple 2.

The initial conditions consist of an equilibrium torus (Fishbone and Moncrief 976; Abramowicz et al. 1978; Komissarov 2006), which is a "torus" of plasma with a black hole at the center. The value of the specific angular momentum of matter and angular momentum of BH ‘a’ determines the total effective potential.

Variable Galactic Gamma-Ray Sources , Heidelberg, Germany

magnetic flux time evolution
Magnetic flux Ψ time evolution

Time evolution of magnetic flux of Dipole model on radius r=4.7 rgleft panel and on horizon central panel,

t=0.00496 sec -- solid,

t=0.0248 sec -- dashed,

t=0.0495 sec -- dot dashed,

t=0.0991 sec -- doted,

t=0.346 sec -- three dots dashed.

Time evolution of magnetic flux of model Quadruple 2 on horizon,

t=0.00496 sec -- solid,

t=0.0248 sec -- dashed,

t=0.1238 sec -- doted,

t=0.4452 sec -- three dots dashed.

Variable Galactic Gamma-Ray Sources , Heidelberg, Germany

slide16
Dipole

Quadruple 1

Quadruple 2

Radial component of magnetic field.

Variable Galactic Gamma-Ray Sources , Heidelberg, Germany

slide17
Quadruple 2. Radial component of magnetic field.

Variable Galactic Gamma-Ray Sources , Heidelberg, Germany

slide18
Flux of matter (MA) - bottom panels and electromagnetic (EM) - up panels

per radian depends on θ and time on radius R=180 rg.

a=0

a=0.9

In our simulations up to ½ of initial electromagnetic flux are transformed to non-relativistic hot wind though numerous shock waves.

It can supply hot corona in such objects as SS433.

Variable Galactic Gamma-Ray Sources , Heidelberg, Germany

lorentz factor
Lorentz factor
  • Distribution of Lorentz factor and magnetic lines for time 0.2075 sec.
  • Cooling case provides most stable and powerful outflow.
  • The Lorentz factor achieves Γ≤ 4.5 (numerical restriction)

No cooling

Modified cooling

Cooling

Variable Galactic Gamma-Ray Sources , Heidelberg, Germany

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