[132.05] Particle acceleration, magnetic field generation, and emission in relativistic shocks

AAS 203rd Meeting, January 2004
Session 132 Gamma Ray Bursts: Processes and Phenomena
Oral, Thursday, January 8, 2004, 2:00-3:30pm, Centennial IV

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[132.05] Particle acceleration, magnetic field generation, and emission in relativistic shocks

K.-I. Nishikawa (NSSTC/NRC), P. Hardee (Univ. of Alabama, Tuscaloosa), G. Richardson (NSSTC/NRC), R. Preece (UAH/NSSTC), H. Sol (Observatore de Paris-Meudon), G.J. Fishman (MSFC/NASA)

Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, two-streaming instability, and the Weibel instability) created in the 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 relativistic jet front propagating through an ambient plasma with and without initial magnetic fields1. We find only small differences in the results between no ambient and weak ambient magnetic fields. Simulations show that the Weibel instability created in the collisionless shock front accelerates particles perpendicular and parallel to the jet propagation direction. While some Fermi acceleration may occur at the jet front, the majority of electron acceleration takes place behind the jet front and cannot be characterized as Fermi acceleration. The simulation results show that this instability is 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 understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.

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The author(s) of this abstract have provided an email address for comments about the abstract: Ken-Ichi.Nishikawa@nsstc.nasa.gov

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