The magnetic field and turbulence of the cosmic web measured using a brilliant fast radio burst

Understand

Fast radio bursts (FRBs) are millisecond-duration events thought to originate beyond the Milky Way galaxy.

• Uncertainty surrounding the burst sources, and their propagation through intervening plasma, has limited their use as cosmological probes.
• We report on a mildly dispersed (dispersion measure 266.5+-0.1 pc cm^-3), exceptionally intense (120+-30 Jy), linearly polarized, scintillating burst (FRB 150807) that we directly localize to 9 arcmin^2.
• Based on a low Faraday rotation (12.0+-0.7 rad m^-2), we infer negligible magnetization in the circum-burst plasma and constrain the net magnetization of the cosmic web along this sightline to <21 nG, parallel to the line-of-sight.