Synchrotron Polarization of Gamma-Ray Burst Afterglow Shocks with Hydrodynamic-scale Turbulent Magnetic Field

Understand

Afterglows of gamma-ray bursts (GRBs) are emitted from expanding forward shocks, which are expected to have magnetic field much stronger than the interstellar field, although the origin of the field is a long-standing problem.

• Two field amplification mechanisms, plasma kinetic instabilities and magnetohydrodynamic instabilities, have been discussed so far.
• The coherence length scales of the fields amplified by these two processes are different by $7-10$ orders of magnitudes, and the polarimetric observations may distinguish them.
• We construct a semi-analytic model of the forward shock afterglow polarization under the assumption of hydrodynamic-scale turbulent magnetic field.