Magnetic Field Reversal around an Active Fast Radio Burst

Understand

The environment of actively repeating fast radio bursts (FRBs) has been shown to be complex and varying.

• The recently localized FRB 20190520B is extremely active, has the largest confirmed host dispersion measure, and is only the second FRB source associated with a compact, persistent radio source (PRS).
• The main tracer of the magneto-ionic environments is the rotation measure (RM), a path-integral of the line-of-sight component of magnetic field strength (B) and electron density, which does not allow a direct probe of the B-field configuration.
• Here we report direct evidence for a B-field reversal based on the observed sign change and extreme variation of FRB 20190520B's RM, which changed from $\sim10000$ rad m$^{-2}$ to $\sim-16000$ rad m$^{-2}$ between June 2021 and January 2022.