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Abstract: Radiation from GRBs in the prompt phase, flares and an afterglow is thoughtto be produced by accelerated electrons in magnetic fields. Such emission maybe produced at collisionless shocks of baryonic outflows or at reconnectionsites at least for the prompt and flares of the magnetically dominatedPoynting flux driven outflows, where no shocks presumably form at all. Anastonishing recent discovery is that during reconnection strong small-scalemagnetic fields are produced via the Weibel instability, very much like theyare produced at relativistic shocks. The relevant physics has been successfullyand extensively studied with the PIC simulations in 2D and, to some extent, in3D for the past few years. We discuss how these simulations predict theexistence of MeV-range synchrotron-jitter emission in some GRBs, which can beobserved with Fermi. Recent results on modeling of the spectral variability andspectral correlations of the GRB prompt emission in the Weibel-jitter paradigmapplicable to both baryonic and magnetic-dominated outflows is reviewed withthe emphasis on observational predictions.

Author: Mikhail V. Medvedev KU


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