Generation of Magnetic Fields in the Relativistic Shock of Gamma‐Ray Burst Sources

TLDR

Synchrotron emission from GRB afterglows is radially polarized. The study aims to test magnetic field generation by detecting polarization scintillations. The two‑stream instability produces magnetic fields up to 10⁻⁵–10⁻¹ of equipartition, aligned with the shock front and varying on skin‑depth scales, which should cause polarization scintillations in GRB afterglows.

Abstract

We show that the relativistic two-stream instability can naturally generate strong magnetic fields with 10-5-10-1 of the equipartition energy density, in the collisionless shocks of gamma-ray burst (GRB) sources. The generated fields are parallel to the shock front and fluctuate on the very short scale of the plasma skin depth. The synchrotron radiation emitted from the limb-brightened source image is linearly polarized in the radial direction relative to the source center. Although the net polarization vanishes under circular symmetry, GRB sources should exhibit polarization scintillations as their radio afterglow radiation gets scattered by the Galactic interstellar medium. Detection of polarization scintillations could therefore test the above mechanism for magnetic field generation.