Particle Acceleration, Magnetic Field Generation, and Emission in Relativistic Shocks.pdf

a r X i v : a s t r o - p h / 0 4 1 0 2 6 6 v 3 4 J a n 2 0 0 5 Particle Acceleration, Magnetic Field Generation, and Emission in Relativistic Shocks K.-I. Nishikawa, a P. Hardee, b C. B. Hededal, c G. Richardson, d R. Preece, e H. Sol, f and G. J. Fishman g aNational Space Science and Technology Center, Huntsville, AL 35805 USA bDepartment of Physics and Astronomy, The University of Alabama, Tuscaloosa, AL 35487 USA cNiels Bohr Institute, Department of Astrophysics, Juliane Maries Vej30, 2100 K?benhavn ?, Denmark dDepartment of Mechanical and Aerospace Engineering University of Alabama in Huntsville Huntsville, AL 35899 USA eDepartment of Physics, University of Alabama in Huntsville, Huntsville, AL 35899 and National Space Science and Technology Center, Huntsville, AL 35805 USA fLUTH, Observatore de Paris-Meudon, 5 place Jules Jansen 92195 Meudon Cedex, France gNASA-Marshall Space Flight Center, National Space Science and Technology Center, Huntsville, AL 35805 USA Abstract Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., Buneman,Weibel and other two-stream instabilities) created in collisionless shocks are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a rela- tivistic jet front propagating into an ambient plasma. We find small differences in the results for no ambient and modest ambient magnetic fields. Simulations show that the Weibel instability created in the collisionless shock front accelerates jet and ambient particles both perpendicular and parallel to the jet propagation direction. The small scale magnetic field structure generated by the Weibel instability is ap- propriate to the generation of “jitter” radiation from deflected electrons (positrons) as opposed to synchrotron radiation. The jitter radiation resulting from small scale