Particle Acceleration in Relativistic Shock Waves

1
Particle Acceleration in Relativistic Shock Waves

• Masahiro HOSHINO
• University of Tokyo

Collaboration with T. Amano, K. Nagata, C.
Jaroschek, Y. Takagi
2
Cosmic Accelerator in Astrophysics

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

Crab Nebula
GRB model
AGN jet (M87)
3
Generic Acceleration Mechanisms
? shock waves - diffusive shock acceleration -
direct acceleration ? magnetic reconnection ?
double layer ? turbulence ? unipolar inductor
(e.g. pulsar magnetosphere) ? etc.
4
Diffusive Shock Acceleration
shock front
Fermi Model
MHD waves
MHD waves
V1
V2
Blandford Ostriker, 1978 Bell 1978
downstream
upstream
5
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.

6
Shock Numerical Experiment
Modeling on Collisionless Shock
Particle-in-Cell (PIC) Simulation
Bz
z
Ey
wall
y
e,e-
x
injection
reflection
108 particles
7
Relativistic Shocks

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

8
Relativistic Shocks

• Pair (positron-electron) Plasma Shock
• s 1 (Poynting flux dominated)
• sltlt 1 (Kinetic flux dominated)
• Ion and Electron Shock

9
Shock Heating for s0.1
shock front
injection
relativistic Maxwellian
wall
upstream
downstream
EM waves are strong No nonthermal Acceleration
Langdon et al. PRL 1988, Gallant et al. ApJ 1992
10
Shock Acceleration for s10-4
relativistic Maxwellian
injection
shock front
wall
upstream
downstream
nonthermal particles

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

11
Shock Surfing Acceleration
z
Sagdeev and Shapiro (1973), Katsouleas and
Dawson (1983)
y
Bz
Ey
? charge
Current Sheet Shock Surfing
? charged particles
?
Near the Shock Front
x
? -charge
shock surface
This can provide unlimited acceleration
Hoshino PTP 2001, Nagata 2005
12
s dependence
s10-1
s10-2
s10-4
s10-3
Nonthermal
slt 10-3 ? strong non-thermal acceleration s
10-2 ? marginal
13
Relativistic Shocks

• Pair (positron-electron) Plasma Shock
• s 1 (Poynting flux dominated)
• sltlt 1 (Kinetic flux dominated)
• Ion and Electron Shock

14
Wakefield Acceleration in Relativistic Shock Wave
upstream(supersonic flow)
downstream(sub-sonic)
Ux,ion
Ux,ele
Bz (EM,photon)
Ex (ES,plasmon)
X
15
Electron Energy Spectra
Accelerated electron energy is more than upstream
ion bulk flow energy
emax/e0 gt Mi/me (50)
16
Wakefield Acceleration
Wakefield (plasmon, Langmuir Wave)
Electron
Laser Pulse (photon, Electromagnetic Wave)
Vph c
Tajima Dawson, PRL 1979
17
Wakefield Acceleration
Ux,ion
Ux,ele
Uy,ele
Ex
Nele
Bz
18
Forward Raman Scattering
19
Maximum Energy of Electron
Resonance under a traveling potential
tt3
Phase Speed Wakefield
tt2
tt1
c/wp
Maximum Energy of Electrons
Maximum Amplitude of Wakefield
20
Forward Backward Wakefield Accelerations
upstream
downstream
21
Wakefield Acceleration in Relativistic Shock Wave
upstream(supersonic flow)
downstream(sub-sonic)
Ux,ion
Ux,ele
Bz (EM,photon)
Ex (ES,plasmon)
X
22
Backward Raman Scattering
(pump)
(w0,k0)
(w2,k2)
(w1,k1)
23
Summary

• Pair Plasma (Electron-Positron) Shock
• Thermal Plasmas for s1
• Nonthermal Particle for s ltlt 1
• by Surfing Acceleration
• (2) Ion-Electron Shock
• - Nonthermal Electrons
• by Wakefield Acceleration