Gamma‐Ray Burst Afterglow: Polarization and Analytic Light Curves

GRB afterglow polarization is discussed. We find an observable, up to 10%,polarization, if the magnetic field coherence length grows at about the speedof light after the field is generated at the shock front. Detection of apolarized afterglow would show that collisionless ultrarelativistic shocks cangenerate strong large scale magnetic fields and confirm the synchrotronafterglow model. Non-detection, at a 1% level, would imply that either thesynchrotron emission model is incorrect, or that strong magnetic fields, afterthey are generated in the shock, somehow manage to stay un-dissipated at``microscopic'', skin depth, scales. Analytic lightcurves of synchrotronemission from an ultrarelativistic self-similar blast wave are obtained for anarbitrary electron distribution function, taking into account the effects ofsynchrotron cooling. The peak synchrotron flux and the flux at frequencies muchsmaller than the peak frequency are insensitive to the details of the electrondistribution function; hence their observational determination would providestrong constraints on blast wave parameters.Comment: 19 pages, submitted to Ap