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Particle Acceleration in Relativistic Shock WavesPowerPoint Presentation

Particle Acceleration in Relativistic Shock Waves

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### Particle Acceleration in Relativistic Shock Waves

Masahiro HOSHINO

University of Tokyo

Collaboration with T. Amano, K. Nagata,

C. Jaroschek, Y. Takagi

Cosmic Accelerator in Astrophysics

- Pulsars & Winds (g ~ 106-7)
- Extragalactic radio source (g ~ 10)
- Gamma ray bursts (g > 100)
- Sources for UHE CR?

Crab Nebula

GRB model

AGN jet (M87)

Generic Acceleration Mechanisms

〇 shock waves

- diffusive shock acceleration

- direct acceleration

〇 magnetic reconnection

〇 double layer

〇 turbulence

〇 unipolar inductor (e.g. pulsar magnetosphere)

○ etc….

Diffusive Shock Acceleration

shock front

Fermi Model

MHD waves

MHD waves

V1

V2

Blandford & Ostriker, 1978

Bell 1978

downstream

upstream

New Challenge in Particle Acceleration

- Diffusive shock acceleration is one of possible models, but slow process…
- Let us find something else in kinetic plasma processes with fast acceleration(direct acceleration mechanisms)
- Surfing Acceleration (e.g. Sagdeev & Shapiro, 1973)
- Wakefield Acceleration (e.g., Tajima & Dawson, 1979)
- etc.

Shock Numerical Experiment

Modeling on Collisionless Shock

Particle-in-Cell (PIC) Simulation

Bｚ

ｚ

Eｙ

wall

ｙ

e+,e-

ｘ

injection

reflection

108 particles

Relativistic Shocks

- Pair (positron-electron) Plasma Shock
- Ion and Electron Shock

Relativistic Shocks

- Pair (positron-electron) Plasma Shock
- σ~ 1 (Poynting flux dominated)
- σ<< 1 (Kinetic flux dominated)

- Ion and Electron Shock

Shock Heating for s=0.1

injection

shock front

relativistic Maxwellian

wall

upstream

downstream

・EM waves are strong

・No nonthermal Acceleration

Langdon et al. PRL 1988, Gallant et al. ApJ 1992

Shock Acceleration for s=10-4

relativistic Maxwellian

injection

shock front

wall

upstream

downstream

nonthermal particles

- EM waves are very strong
- Strong Acceleration occurs at the shock front

Eｙ

Bｚ

Bｚ

positron

X

“Shock Surfing” Accelerationｚ

Sagdeev and Shapiro (1973),

Katsouleas and Dawson (1983)…

ｙ

Bｚ

Eｙ

③

+charge

“Current Sheet” Shock Surfing

①

charged

particles

②

Near the Shock Front

ｘ

③

-charge

shock surface

This can provide unlimited acceleration

Hoshino PTP 2001, Nagata 2005

s dependence

s=10-1

s=10-2

s=10-4

s=10-3

Nonthermal

σ< 10-3 → strong non-thermal acceleration

σ= 10-2 → marginal

Relativistic Shocks

- Pair (positron-electron) Plasma Shock
- σ~ 1 (Poynting flux dominated)
- σ<< 1 (Kinetic flux dominated)

- Ion and Electron Shock

Wakefield Acceleration in Relativistic Shock Wave

upstream（supersonic flow）

downstream（sub-sonic）

Ux,ion

Ux,ele

Bz

(EM,photon)

Ex

(ES,plasmon)

X

Upstream

Electron Energy SpectraAccelerated electron energy is more than upstream ion bulk flow energy

emax/e0 > Mi/me (=50)

Wakefield Acceleration

Wakefield (plasmon,

Langmuir Wave)

Electron

Laser Pulse (photon,

Electromagnetic Wave)

Vph ~ c

Tajima & Dawson, PRL 1979

for electrons

wakefield (vph ~c)

is generated

photon injection from

left-hand boundary

Wakefield AccelerationUx,ion

Ux,ele

Uy,ele

Ex

Nele

Bz

Maximum Energy of Electron

Resonance under a traveling potential

t=t3

Phase Speed Wakefield

t=t2

t=t1

c/wp

Maximum Energy of Electrons

Maximum Amplitude of Wakefield

Same as Laser Wakefield

Ux,ion

Acceleration

toward positive direction

Ux,ele

Bz

Langmuir waves, propagating toward positive direction

Ex

Forward & Backward Wakefield Accelerationsdownstream

upstream

Wakefield Acceleration in Relativistic Shock Wave

upstream（supersonic flow）

downstream（sub-sonic）

Ux,ion

Ux,ele

Bz

(EM,photon)

Ex

(ES,plasmon)

X

Summary

- Pair Plasma (Electron-Positron) Shock
- Thermal Plasmas for σ~1
- Nonthermal Particle for σ << 1
by Surfing Acceleration

(2) Ion-Electron Shock

- Nonthermal Electrons

by Wakefield Acceleration

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