A massive explosion at the edge of the universe revealed its magnetic heart through a subtle twist in its radio waves.
This measurement is the first time anyone has detected Faraday rotation in a gamma-ray burst environment. Scientists used centimeter-wavelength polarization to look at the jet of material flying out of a dying star. The data shows the exact magnetic structure of the jet and the density of the surrounding space. Previously, these explosions were mostly seen as flashes of light without a clear view of their internal magnetic engines. This discovery helps explain how the most violent events in the cosmos can focus so much energy into a narrow beam.
First Detection of Faraday Rotation in a Gamma-Ray Burst Afterglow: Low Polarization and High Rotation Measure in GRB 260310A Reveal Jet Magnetic Structure and Environment
arXiv · 2604.27480
We report the detection of linear polarization in the radio afterglow of GRB 260310A, representing the first centimeter-wavelength polarization detection of a gamma-ray burst (GRB) afterglow and the first measurement of Faraday rotation in a GRB environment. We detect linearly polarized emission across $11-25$ GHz, with a polarization fraction decreasing monotonically from $(3.18 \pm 0.18)\%$ at 25 GHz to $(0.69 \pm 0.22)\%$ at 11 GHz. Interpreting the radio data as emission from a reverse shock