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Session 119 - Gamma Ray Bursts.
Oral session, Saturday, January 10
International Ballroom Center,
The dynamics of relativistic blast waves which decelerate by sweeping up matter from the ISM are studied. Coupled equations for the proton and electron momentum distribution functions in the comoving fluid frame are used to calculate the observed synchrotron radiation spectrum. The results depend critically on the mechanism for transfering energy from the nonthermal protons to the electrons. The simplest prescription is to assume that a fixed fraction of the comoving proton power is instantaneously transformed into a power-law, ``shock''-like electron distribution function. Analytic results for the case of a relativistic plasmoid with a constant magnetic field, and numerical results for the general case are presented and applied to GRB and blazar variability. The delayed X-ray and optical afterglow emission of GRBs are easily understand with this model, which implies that the bulk of the primary GRB emission is nonthermal synchrotron radiation and that the diverse GRB time profiles reflect the density distribution of the ISM. We also propose that radio and gamma-ray flares in blazars are due to the transformation of the directed kinetic energy of the relativistic outflows by interactions with the external medium, as would occur if broad-line region clouds pass through the path of the relativistic outflows.
