Simulation Study of Magnetic Fields generated by …...• The growth rate of the Weibel instability...
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Simulation Study of Magnetic Fields generated by the Electromagnetic Filamentation Instability First GLAST Symposium, February 5 – 8, 2007 For further information: ken- [email protected] K.-I. Nishikawa (NSSTC/UAH), E. Ramirez-Ruiz (IAS/UCSC), P. Hardee (Univ. of Alabama, Tuscaloosa), C. Hededal (Niels Bohr Inst.), Y. Mizuno (NPP/MSFC), G.J. Fishman (NASA/MSFC) Key Scientific questions • How do shocks in relativistic jets evolve? • How are particles accelerated? • What are the dominant radiation processes? • How do 3-D relativistic particle simulations reveal the dynamics of shock fronts and transition regions? • How do shocks in relativistic jets evolve under various ambient plasma and magnetic fields? • How do magnetic fields generated by the Weibel instability contribute to jitter radiation? -- for some answers see Nishikawa et al. 2006, ApJ, 642, 1267 -- Results • The Weibel instability creates filamented currents and density structure along the propagation axis of the jet. • The growth rate of the Weibel instability depends on the Lorentz factor, composition, and strength and direction of ambient B fields. • In a one-dimensional system the Buneman instability is responsible for surfing acceleration. • The Weibel instability is excited in the 3-D system. • In order to understand the complex shock dynamics of relativistic jets, further simulations with additional physical mechanisms such as radiation loss and inverse Compton scattering are necessary. • The magnetic fields created by the Weibel instability generate highly inhomogeneous magnetic fields, which are responsible for Jitter radiation (Medvedev, 2000, 2006; Fleishman 2006). Future plans • Further simulations with a systematic parameter survey will be performed in order to understand shock dynamics • Further diagnostics will be developed • To improve the performance of the code, MPI is implemented and will be used for simulating a lager system • Implement better boundary conditions at the free boundaries • Investigate radiation processes from the accelerated electrons and compare with observations (GRBs, SNRs, AGNs, etc) • Implement radiative losses into the dynamics • Consider relevance to experiments at SLAC Goal: Radiation from collisionless shock GRB Shock simulations Hededal Thesis: ala Hededal & Nordlund 2005 (astro-ph/0511662) Power ☺ (astro-ph/0506559) N(γ) ∝ γ -p -β = -(p - 1)/2 = -0.70 → p = 2.4 Magnetic field energy and parallel and perpendicular velocity space along Z with 3 stages Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves (e.g., Buneman, Weibel, other two-stream instabilities) created in the shock are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic particle-in-cell (RPIC) code, we investigate particle acceleration in relativistic jets. Simulations show that the Weibel instability created at the shock front accelerates particles perpendicular and parallel to the jet propagation direction. This instability is also responsible for generating magnetic fields in the relativistic jets. The simulations show that the growth rate of the Weibel instability depends on the Lorentz factor and composition of the jet, as well as the orientation and strength of the ambient magnetic field. The magnetic fields generated by the Weibel instability create highly nonuniform, small-scale magnetic fields, which contribute to the electron’s transverse deflection. The radiation from electrons in these environments (jitter radiation) is different from synchrotron radiation. Weibel instability x −ev z × B x jet J J current filamentation generated magnetic fields adapted from Medvedev & Loeb, 1999, ApJ 526, 697 (electrons) local, randomly generated magnetic field Growth time: τ growth = γ sh 1/2 /ω pe Length: λ = γ th 1/2 c/ω pe = (γ th / γ sh ) 1/2 τc Growth times of Weibel instability: τ A < τ B < τ C 3-D RPIC simulation geometry Z X Y jet front jet injection plane B 2 γV ‖ γV ⊥ Nonlinear stage Jet head Linear stage Nonlinear stage http://www.astro.ku.dk/~hededal γV distribution functions (parallel, perpendicular to the jet) (Nishikawa et al. 2006) γ = 5 Electron-ion Electron-positron ω pe t ~ 4 τ growth Lorentz boosted thermal distribution for comparison jet Schematic Jet velocity distributions 5 15 Density perturbation by the Weibel instability A: γ = 5 B: γ = 15 Parallel current J z (arrows: J z,x ) Electron-positron jet ω pe t ~ 4 τ growth C: 4 < γ < 100 A B C Properties along the jet for three slices in z γ = 5 γ = 15 4 < γ < 100 E z B x n e Ramirez-Ruiz, Nishikawa & Hededal, 2006 ApJL, submitted Ramirez-Ruiz et al. 2006, ApJ, in preparraion
Transcript of Simulation Study of Magnetic Fields generated by …...• The growth rate of the Weibel instability...
Simulation Study of Magnetic Fields generated by theElectromagnetic Filamentation Instability
First GLAST Symposium, February 5 – 8, 2007For further information: [email protected]
K.-I. Nishikawa (NSSTC/UAH), E. Ramirez-Ruiz (IAS/UCSC), P. Hardee (Univ. of Alabama, Tuscaloosa),C. Hededal (Niels Bohr Inst.), Y. Mizuno (NPP/MSFC), G.J. Fishman (NASA/MSFC)
Key Scientific questions• How do shocks in relativistic jets evolve?• How are particles accelerated?• What are the dominant radiation processes?• How do 3-D relativistic particle simulations revealthe dynamics of shock fronts and transition regions?• How do shocks in relativistic jets evolve under various ambient plasma and magnetic fields?• How do magnetic fields generated by the Weibel instability contribute to jitter radiation?
-- for some answers see Nishikawa et al. 2006, ApJ, 642, 1267 --
Results• The Weibel instability creates filamented currents and density structure along the propagation axis of the jet.• The growth rate of the Weibel instability depends on the Lorentz factor, composition, and strength and direction of ambient B fields.• In a one-dimensional system the Buneman instability is responsible for surfing acceleration.• The Weibel instability is excited in the 3-D system.• In order to understand the complex shock dynamics of relativistic jets, further simulations with additional physical mechanisms such as radiation loss and inverse Compton scattering are necessary.• The magnetic fields created by the Weibel instability generatehighly inhomogeneous magnetic fields, which are responsible for Jitter radiation (Medvedev, 2000, 2006; Fleishman 2006).
Future plans• Further simulations with a systematic parameter survey will be performed in order to understand shock dynamics• Further diagnostics will be developed• To improve the performance of the code, MPI is implemented and will be used for simulating a lager system• Implement better boundary conditions at the free boundaries• Investigate radiation processes from the accelerated electrons and compare with observations (GRBs, SNRs, AGNs, etc)• Implement radiative losses into the dynamics• Consider relevance to experiments at SLAC
Goal: Radiation from collisionless shock
GRB Shock simulations
Hededal Thesis:
ala Hededal & Nordlund 2005 (astro-ph/0511662)
Pow
er
☺
(astro-ph/0506559)
N(γ) ∝ γ-p -β = -(p - 1)/2 = -0.70 → p = 2.4
Magnetic field energy and parallel and perpendicular velocity space along Z with 3 stages
Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves (e.g., Buneman, Weibel, other two-stream instabilities) created in the shockare responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic particle-in-cell (RPIC) code, we investigate particle acceleration inrelativistic jets. Simulations show that the Weibel instability created at the shock front accelerates particles perpendicular and parallel to the jet propagationdirection. This instability is also responsible for generating magnetic fields in the relativistic jets. The simulations show that the growth rate of the Weibelinstability depends on the Lorentz factor and composition of the jet, as well as the orientation and strength of the ambient magnetic field. The magnetic fieldsgenerated by the Weibel instability create highly nonuniform, small-scale magnetic fields, which contribute to the electron’s transverse deflection. The radiationfrom electrons in these environments (jitter radiation) is different from synchrotron radiation.
Weibel instability
x−evz × Bx
jet
J
J
currentfilamentation
generatedmagnetic fields
adapted from Medvedev & Loeb, 1999, ApJ 526,697
(electrons)
local, randomly generatedmagnetic field
Growth time: τgrowth = γsh
1/2/ωpe
Length: λ = γth
1/2c/ωpe = (γth/ γsh)1/2 τc
Growth times of Weibel instability:
τA< τB < τC
3-D RPIC simulationgeometry
Z
X
Y
jet front
jetinjection plane
B2 γV‖ γV⊥
Nonlinear stage Jethead
Linear stage Nonlinear stage
http://www.astro.ku.dk/~hededal
γV distribution functions (parallel, perpendicular to the jet)
(Nishikawa et al. 2006)
γ = 5
Electron-ion Electron-positron
ωpet ~ 4 τgrowth
Lorentz boostedthermaldistribution forcomparison
jet
Schematic Jet velocity distributions
5 15
Density perturbation by the Weibel instability
A: γ = 5
B: γ = 15
Parallel current Jz (arrows: Jz,x)
Electron-positron jetωpet ~ 4 τgrowth
C: 4 < γ < 100
A B
C
Properties along the jet for three slices in z
γ = 5 γ = 15 4 < γ < 100
Ez
Bx
ne
Ramirez-Ruiz, Nishikawa & Hededal, 2006 ApJL, submitted Ramirez-Ruiz et al. 2006, ApJ, in preparraion
