1. Radiation from Poynting Jets and Collisionless Shocks Edison Liang, Koichi Noguchi Shinya Sugiyama, Rice University Acknowledgements: Scott Wilks, Bruce Langdon Bruce Remington Talk given at AAS Seattle Meeting January 2007

2. Internal shocks Hydrodynamic Outflow Poynting flux Electro-magnetic -dominated outflow Two Paradigms for the Energetics of Relativistic Jets in Blazars & GRBs e+e- ions e+e- What is primary energy source? How are the e+e- accelerated? How do they radiate? shock  -rays SSC, EC…  -rays B Synchrotron Radiation is usually assumed in All paradigms

3. We have developed a Particle-In-Cell code that simultaneously computes radiation output from each superparticle self-consistently. We find that in-situ radiation output from electrons accelerated by Poynting flux and relativistic collisionless shocks are much below that predicted by the classical synchrotron formula. This is because the highest energy electrons are preferentially accelerated by Lorentz forces that are parallel, not perpendicular, to the particle momentum.

4. From PIC runs, we compute the radiation power directly from the force terms P rad = 2e 2 (F || 2 +  2 F + 2 ) /3cm 3 where F || is force along v and F + is force orthogonal to v (algorithm is carefully calibrated against analytic formula using monoenergetic electrons radiating in a uniform static B-field) For Poynting flux acceleration, we find that P rad ~  e 2  2 sin 4  << P syn ~  e 2  2 where  is angle between v and Poynting vector k. Also critical frequency  cr ~  e  2 sin 2  crsyn

5. This result Radiation efficiency << classical synchrotron can be understood as follows: The most efficient accelerations to higher  are produced by Lorentz forces parallel to the particle momentum. But only forces perpendicular to particle momentum can produce synchrotron radiation.

6. B e+e-Poynting jet running into cool e-ion ambient plasma (movie by Noguchi)

7. By Ez Jz Plasma JxB force snowplows all surface particles upstream: ~ max(B 2 /4  nm e c 2, a o ) “Leading Ponderomotive Accelerator” (LPA) Plasma JxB force pulls out surface particles. Loaded EM pulse (speed < c) stays in-phase with the fastest particles, but gets “lighter” as slower particles fall behind. It accelerates indefinitely over time: >> B 2 /4  nm e c 2, a o “Trailing Ponderomotive Accelerator” (TPA). (Liang et al. PRL 90, 085001, 2003) Entering Exiting Poynting Flux: Particle acceleration by induced j x B(ponderomotive) force x x EM pulse By x y z Ez Jz JxB k

8. P rad P analytic =  e 2  2 sin 4  x pxpx pzpz ByBy P rad Electrons snowplowed by Poynting flux radiates at a level ~ 10 -4 of synchrotron formula using local B and . This is due to sin  ~ p z /p x < 0.1.

9. Momentum gets more and more Anisotropic with time: p z /p x <<1 Details of TPA expansion

10. The power-law index seems remarkably robust independent of initial plasma size or temperature and only weakly dependent on B f(  )  -3.5 L o =10 5 r ce L o = 10 4 r ce

11. P rad P analytic =  e 2  2 sin 4  In TPA, we also see good correlation between P rad and P analytic

12. Poynting Jet P rad asymptotes to ~ constant level at late times as increase in  is compensated by decrease in  and B L o =120c/  e L o =10 5 c/  e p o =10 P rad 10*B y P rad xx x

13. Asymptotic P rad scales as (  e /  pe ) n with n ~ 2 - 3  e /  pe =10 2 10 3 10 4 x x x P rad

14. Inverse Compton scattering against ambient photons can slow or stop acceleration (Sugiyama et al 2005) n  =10 -4 n e n  =10 -2 n e n  =n e 1 eV BB ambient photon field  e  pe =100 jet

15. Next we study radiation from Collisionless Shocks 3 Examples: 1.e+e-/e+e- Magnetized Shock (B 2 ~ bulk KE) 2.e+e- /e-ion Magnetized Shock (B 2 ~ bulk KE) 3.e+e- Nonmagnetized Shock (B 2 << bulk KE)

16. pxpx B y *100 f(  )  Magnetic Shock of e+e- sweeping up cold ambient e+e- shows broad (>> c/  e, c/  pe ) transition region with 3-phases (n ej =40n o ) ejecta ambient decelerated ejecta spectral evolution swept-up ambient spectral evolution  x x

17. pzpz pxpx Both ejecta and swept-up electrons are highly anisotropic: p z <<p x ejecta swept-up

18. ejecta e- Swept-up ambient e- P rad of swept-up electron is lower than P rad of decelerating ejecta electron. The radiative layer is very thin P rad x x

19. ejecta e+ ejecta e- ambient ion ambient e-  f(  ) -10p xe -10p xej 100p xi 100E x 100B y P rad Magnetic shock in e+e-/e-ion plasma is very complex with 5 phases and broad transition region(>> c/  i, c/  pe ). Swept-up electrons are accelerated by ponderomotive force. Swept-up ions are accelerated by charge separation electric fields. x

20. ejecta e-swept-up e- P rad of shocked swept-up electrons is comparable to the e+e-/e+e- case. But the radiation layer is much thicker x x P rad

21. Comparison of collisionless shocks: e+e- shocking B=0 e+e- cold plasma ejecta: hi-B, hi-  weak-B, moderate  B=0, low  swept-up 100B y ejecta p x swept-up p x 100B y 100E x 100B y 100E x -p x swept-up -p xswrpt-up ejecta no power-law ~ -3 power-law f(  )   

22. ejecta Nonmagnetic e+e-/e+e- shock: Radiation not Dominated By Weibel turbulence ejecta -p x swept-up p x n swept-up Ex2Ex2 n ejecta By2By2 time ejecta energy swept-up energy E x energy B y energy energy evolution P rad swept-up P rad ejecta x x

23. SUMMARY 1.Radiation power of Poynting jets are many orders of magnitude below classical synchrotron formula due to anisotropy of acceleration (Forces ~ parallel to velocity are most efficient in acceleration). 2.Structure and radiation power of collisionless shocks are highly sensitive to ejecta (upstream) B field strength and Lorentz factor. 3. Radiation power of collisionless shocks are also much lower than classical synchrotron formula for a given ejecta magnetic field and Lorentz factor. The highest energy particles are accelerated mainly by (electrostatic or ponderomotive) forces parallel to the velocity. 4. Swept-up electrons are accelerated by ponderomotive and/or electrostatic forces. Swept-up ions are accelerated by electrostatic force caused by charge separation.