Linear and circular polarization in GRB afterglows

Understand

A certain degree of linear polarization has been measured in several GRB afterglows.

• More surprisingly, circular polarization has been recently measured in GRB121024A.
• For synchrotron emission, the polarization level depends on: (i) the local magnetic field orientation (ii) the geometry of the emitting region with respect to the line of sight and (iii) the electron pitch-angle distribution.
• For this reason, polarization measurements are a valuable tool to probe afterglow micro-physics.