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V. Petrosian, N.M. Lloyd (Stanford University)
The synchrotron mechanism appears to be the most viable candidate for production of prompt gamma-ray and afterglow emissions. It is generally believed that these processes take place behind relativistic shocks, referred to as internal and external shocks, respectively. An internal shock arises from merger of relativistic shells of (relatively) cool gas when a fast shell overtakes a slower one. An external shock can arise from the interaction of such a shell with the external medium (interstellar gas or progenitor stellar wind). These shells are presumably the outcomes of fireballs arising from episodic accretion of chunks of matter onto a black hole. The outstanding question in this scenario for production of the radiation is the process of conversion of the kinetic (and perhaps the internal) energy of these interactions, which is carried mainly by protons into relativistic electrons and synchrotron photons. A model will be outlined whereby, behind the shock, the proton energy is converted into plasma turbulence, which in turn accelerates electrons stochastically. The details of the plasma instabilities that lead to the production of plasma waves and the resonant interactions of these waves with electrons (and protons) will be described.
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