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arXiv · 0707.4381

Electron-Positron Pair Loading and the Origin of the Upstream Magnetic Field in GRB Shocks

Enrico Ramirez-Ruiz·Ken-Ichi Nishikawa·Christian B. Hededal
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Abstract

We investigate here the effects of plasma instabilities driven by rapid electron/positron pair cascades, which arise in the environment of GRB sources as a result of back-scattering of a seed fraction of the original spectrum. The injection of electron/positron pairs induces strong streaming motions in the ambient medium. One therefore expects the pair-enriched medium ahead of the forward shock to be strongly sheared on length scales comparable to the radiation front thickness. Using three-dimensional particle-in-cell simulations, we show that plasma instabilities driven by these streaming electron/positron pairs are responsible for the excitation of near-equipartition, turbulent magnetic fields. Our results reveal the importance of the electromagnetic filamentation instability in ensuring an effective coupling between electron/positron pairs and ions, and may help explain the origin of large upstream fields in GRB shocks.

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Enrico Ramirez-Ruiz, Ken-Ichi Nishikawa, Christian B. Hededal. 2007-07-30. Electron-Positron Pair Loading and the Origin of the Upstream Magnetic Field in GRB Shocks. https://doi.org/10.1086/522072

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