GRB Afterglow Polarimetry: Past, Present and Future
  Gamma-ray bursts and their afterglows are thought to be produced by an
ultrarelativistic jet. One of the most important open questions is the outflow
composition: the energy may be carried out from the central source either as
kinetic energy (of baryons and/or pairs), or in electromagnetic form (Poynting
flux). While the total observable flux may be indistinguishable in both cases,
its polarization properties are expected to differ markedly. The later time
evolution of afterglow polarization is also a powerful diagnostic of the jet
geometry. Again, with subtle and hardly detectable differences in the output
flux, we have distinct polarization predictions.
