Particle Acceleration and Radiation from Relativistic Colliding Plasmas

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~10 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- B B=0

9. We use ray-tracing to compute the intensity and critical frequencies of radiation measured by detector Use approximation: I = Pradg2/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 ejecta px 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 plasma B (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. pi px/mc ambient ion ambient e- 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 ~ 2.5-2.8 5. In strongly magnetized shocks, swept-up electrons are accelerated by ponderomotive force and electrostatic turbulence. Swept-up ions are accelerated by charge separation.