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**Session 119 - Gamma Ray Bursts.**

*Oral session, Saturday, January 10*

*International Ballroom Center, *

## [119.02] Electron Acceleration and Synchrotron Radiation in Relativistic Blast Waves: Applications to GRBs and Blazars

*C. D. Dermer (NRL), J. Chiang (NRC/NRL)*
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.

**Program
listing for Saturday**