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K.-I. Nishikawa (NSSTC), E. Ramirez-Ruiz (IAS), P. Hardee (UA), C. Hededal (Niels Bohr Inst.), C. Kouveliotou, G. J. Fishman (MSFC/NASA), Y. Mizuno (NRC/MSFC)
Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, two-streaming instability, and the Weibel instability) created by relativistic jets are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code with a longer simulation system than our previous simulations, we have investigated particle acceleration associated with a relativistic jet propagating through an ambient plasma without initial magnetic fields. The growth rate of the Weibel instability depends on the properties of jet. Simulations show that the Weibel instability created in the collisionless shock accelerates particles perpendicular and parallel to the jet propagation direction. The current channels generated by the Weibel instability are surrounded by toroidal magnetic fields and radial electric fields. E x B forces do accelerate some jet particles to higher energies in the parallel direction in addition to acceleration in the perpendicular directions relative to the initial motion.
The simulation results show that these instabilities are responsible for generating and amplifying highly nonuniform, small-scale magnetic fields, which contribute to the electron's transverse deflection behind the jet head. The ``jitter'' radiation from deflected electrons has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to the understanding of the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants. We will examine our simulation results to address the early afterglows observed with SWIFT.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.