Relativistic MHD Simulations of jets

1
Relativistic MHD Simulations of jets
Y. Mizuno1,2,5Yosuke.Mizuno_at_msfc.nasa.gov K.-I.
Nishikawa2,3, P. Hardee3, S. Koide4 , G. J.
Fishman1 1 NASA/Marshall Space Flight Center, 2
National Space Science and Technology Center, 3
University of Alabama, 4 Department of
Engineering, Toyama University, 5 NRC Research
fellow
Abstract
We have performed 3D RMHD simulations to
investigate the stability and structure of highly
relativistic MHD precessed jets with three
different frequencies. As initial condition
preexisting jet flow is established across the
computational volume an input the precessional
perturbation from the inner boundary. We show the
results from simulations of a super-magnetosonic
jet surrounded by a fast wind. The simulation
results reveal complex pressure structure inside
the RMHD jet. The structure will be produced by a
combination of the helical surface and body modes
excited by the precession. The jet strongly
interacts with the external wind. It means
significant energy loss from the jet surface.
1.Introduction
2.Simulation model

• Relativistic jets can exhibit time-dependent
  curved structures with superluminally moving
  component (3C345 etc.) or with both
  superluminally moving and more slowly moving or
  stational components (M87, 3C120 etc.).
• Superluminal motions along curved trajectories
  can be explained by helical jet model.
• Helical patterns are the expected result for
  Kelvin-Helmholtz and Current-driven jet
  instabilities in relativistic flows.

• The numerical code
• 3D relativistic MHD code (Koide et al. 2000
  Koide 2003 Mizuno et al. 2004) with Cartesian
  coordinates.
• The initial condition
• preexisting jet flow is established across the
  computational volume (the case in which a leading
  Mach disk and bow shock have passed) and leaving
  in a pressure balance with a low-density external
  wind (rj/rext2.0).
• The jet flow vj0.9165c, Lorentz factor g2.5
  and external wind vext0.5c
• Adiabatic index G5/3, sound speed aext0.7155c,
  aj0.6446c, and Alfven speed va,ext0.06457c,
  va,j0.06127c. The jets are super-magnetosonic
  flows
• We set vertical magnetic field (Bz,j0.1
  (r0c2)1/2, Bz,ext0.95Bz,j) along the jet
• We input precessional perturbation with
  transverse velocity (vt0.01c, 0.1c) and
  perturbation frequency (wRj/vj 0.4, 0.93, 2.69)
  from the inner boundary
• Numerical region and Mesh points
• -3 Rj lt x,y lt 3Rj, 0 Rj lt z lt 20Rj with 90 90
  300 mesh points

z direction
Our propose

• We investigate a detailed analysis of the
  time-dependent structures of relativistic jets by
  using 3D relativistic MHD simulations.

Schematic picture of Jet head region
Simulation region
3.Results
1D Slices (parallel to the jet axis located at
x/Rj0.12(solid line), 0.33(dashed line),
0.53(dashed-dotted line))

• Previous works for 3D relativistic hydro
  simulations (Hardee et al. 2001)
• rj/rext10.0, vj0.9165, vext0.0
• adiabatic index G5/3, sound speed aext0.6121c,
  aj0.2753c
• precessional perturbation with transverse
  velocity (vt0.01c) and perturbation frequency
  (wRj/vj 0.4, 0.93, 2.69)

Vt0.01 case
vr
vf
vz
wRj/vj
Pgas
Bz
vr
vf
Pgas
Br
gzvz
0.4
0.4
0.93
0.93
2.69
2.69

• Axial velocities near the jet axis in slow
  transverse velocity case show that all of the
  simulations are in linear regime for initial
  transverse velocity (especially high-frequency
  case shows the classic linear exponential
  growth). In previous works of 3D hydro case
  (Hardee et al. 2002) the simulations are fully
  evolved out to about 30 Rj for the low- and
  moderate-frequency. Therefore we need more longer
  simulations to check the simulations are fully
  evolved out.
• From comparison to 3D hydro case the simulation
  results show the similar tendency. However
  amplitude of velocities in 3D MHD case are much
  larger than 3D hydro case. It is because the
  effect of magnetic field and external wind. We
  need analytical works to investigate more detail.
  
• In fast transverse velocity case the simulations
  of middle- and high-frequency cases are fully
  evolved out and tend to non-linear regime.
• The radial magnetic field in meddle-frequency
  case shows substructure. It can be explained by
  the fluctuations in the axial velocity and
  pressure.
• The results of high-frequency cases with fast
  transverse velocity is very complicated. We
  suspect the simulations show the results of a
  beat frequency between helical surface and first
  body mode. It leads to the decrease in radial
  magnetic field and radial velocity.
• We need theoretical analysis to understand the
  complicated structure of these simulation
  results.

Vt0.1 case
wRj/vj
Bz
vr
vf
Pgas
Br
gzvz
0.4
0.93
2.69
4.Summary and Future work
2D Plot (x-y plane, z/Rj15) of high-frequency
case (wRj/vj2.69)

• We have performed 3D RMHD simulations to
  investigate the stability and structure of highly
  relativistic MHD precessed jets.
• The simulation results reveal complex pressure
  structure inside the RMHD jet.
• The structure will be produced by a combination
  of the helical surface and body modes excited by
  the precession.
• The jet strongly interact with external wind. It
  means significant energy loss from the jet
  surface.
• To investigate the more detail of jet structure,
  we need theoretical works based on normal mode
  analysis.
• As future works we will plan to investigate the
  effect of external wind and in the regime of
  sub-magnetosonic relativistic jet flow.

Vt0.01 case
Vt0.1 case

• The jet interact with external wind.
• In fast transverse velocity case the pressure
  structure is more complicated and more strongly
  interact with external wind. It is because the
  simulation becomes non-linear phase.
• It expect significant energy loss from the jet
  surface.