1. Particle Acceleration and Radiation from Relativistic Colliding Plasmas
Edison Liang, Koichi Noguchi
Orestes Hastings, Rice University
Acknowledgements: Scott Wilks, Giovanni
Lapenta, Bruce Remington
Talk given at DPP meeting 2007
Work partially supported by NSF, LLNL, LANL

2. Blazars, Gamma-ray Bursts, Pulsar Wind Nebulae efficiently convert outflow energy from a central engine into high-energy radiation. How do relativistic plasma collisions and interactions dissipate their energy and radiate?
To address this, We have developed a PIC code that includes in-situ radiation from each superparticle self-consistently, allowing for radiation damping and Compton drag if necessary.

3. Electrostatic 2-stream and Weibel instabilities are dominant
dissipation mechanisms in unmagnetized collisions
Head-on collision of cold e+e- plasmas at 0.9c in 1-D leads to
growth of pure electrostatic 2-stream instability. No electron holes
are formed. Some particles are accelerated to to twice initial energy

4. Px vs x
By vs x
Head-on e+e- collision of e+e- at 0.9c in 3D leads to Weibel
Instability using Quicksilver. Early growth of field energies
agrees with linear theory. Some particles are accelerated to
energies > twice initial energy (Hastings & Liang 2007)

5. Comparison of collisions: hot e+e- running into B=0 e+e- cold plasma
Ejecta: low-By, G~ B=0, NR
100By
100Ex
100By
Weibel is inhibited
relative to 2-stream.
2.7 power law is
produced in the
relativistic case, in
agreement with
other groups.
100Ex
-px swept-up
-pxswrpt-up
2.7
ejecta
ejecta
swept-up
swept-up

6. PIC simulation can compute the
radiation power directly from the force terms
Prad = 2e2(F|| 2+ g2F+2) /3c
where F|| is force along v
and F+ is force orthogonal to v

7. Calibration of PIC calculation again analytic formula
Ppic
Psyn

8. Simulation of warm magnetized e+e- colliding with B=0 e+e-

9. We use ray-tracing to compute the intensity and critical
frequencies of radiation measured by detector
Use approximation:
I = Prad g2/p for q≤g-1
I=0 for q > g-1
wcr= reciprocal of time it takes emission cone to
Sweep past detector
Detector

10. Details of e+e- Poynting Shock (nejecta=40no)
By*100 px
ejecta
ambient
f(g)
decelerated
ejecta
spectral
evolution
swept-up
ambient
spectral
evolution g g

11. Movie showing e+e- “Poynting Jet” sweeping up cold e-ion plasmaB
(movie made by Noguchi)

12. Poynting shock with e-ion plasma is very complex. Swept-up electrons
are accelerated by ponderomotive (jxB) force. Swept-up ions are
accelerated by charge separation electric fields.
100pxi
100By
Prad
100Ex
f(g)
ejecta e+
-10pxe
-10pxej
ambient
ion
ejecta e-
ambient e- g

13. Poynting shock of e+e- sweeping up cold e-ion plasma:
Poynting flux decays via mode conversion and acceleration
and heating of electrons.
px/mc pi
ambient e-
ambient ion
ejecta e+ x
pi*10 By
By*100

14. Evolution of f(g) vs . g
ejecta e-
ejecta e+
swept-up e-
ion

15. SUMMARY
Structure and radiative power of collisionless shocks are highly dependent on ejecta (downstream) B field and Lorentz factor.
Radiative efficiency appears to be low in all cases. This may pose a
problem for astrophysics, especially GRBs and blazars.
3. In Weibel shocks, electrons are accelerated by self-generated EM
turbulence. No evidence of first-order Fermi process.
In electrostatic shocks, electrons are accelerated by Langmuir
turbulence to form power-law of index ~
5. In strongly magnetized shocks, swept-up electrons are accelerated by ponderomotive force and electrostatic turbulence. Swept-up ions are accelerated by charge separation.