AIP Conference Proceedings
Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks, e.g., gamma-ray bursts (GRBs), active galactic nuclei (AGNs), and microquasars commonly exibit power-law emission spectra. Recent PIC simulations of relativistic electro-ion (or electron-positron) jets injected into a stationary medium show that particle acceleration occurs within the downstream jet. In collisionless, relativistic shocks, particle (electron, positron, and ion) acceleration is due to plasma waves and their associated instabilities (e.g., the Weibel (filamentation) instability) created in shock region. The simulations show that the Weibel instability in responsible for generating and amplifying highly non-uniform, small-scale magnetic fields. These fields contribute to the electron's transverse deflection behind the jet head. The resulting "jitter" radiation from deflected electrons has different properties compared to synchrotron radiation, which assumes a uniform magnetic field. Jitter radiation may be important for understanding the complex time evolution and/or spectra in gamma-ray bursts, relativistic jets in general, and supernova remnants.
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