Sudden polarization angle jumps of the repeating fast radio burst FRB 20201124A

TL;DR

This paper reports the first observation of orthogonal polarization angle jumps in a repeating FRB, indicating that its emission likely originates from a highly magnetized magnetar magnetosphere, similar to pulsars.

Contribution

It provides the first detection of pulsar-like polarization jumps in an FRB, linking FRB emission mechanisms to magnetar magnetospheres.

Findings

Orthogonal polarization angle jumps observed in over two thousand bursts.

Jumps suggest superposition of two emission modes in a highly magnetized plasma.

Emission regions are smaller than the light cylinder, indicating a magnetospheric origin.

Abstract

We report the first detection of polarization angle (PA) orthogonal jumps, a phenomenon previously only observed from radio pulsars, from a fast radio burst (FRB) source FRB 20201124A. We find three cases of orthogonal jumps in over two thousand bursts, all resembling those observed in pulsar single pulses. We propose that the jumps are due to the superposition of two orthogonal emission modes that could only be produced in a highly magnetized plasma, and they are caused by the line of sight sweeping across a rotating magnetosphere. The shortest jump timescale is of the order of one-millisecond, which hints that the emission modes come from regions smaller than the light cylinder of most pulsars or magnetars. This discovery provides convincing evidence that FRB emission originates from the complex magnetosphere of a magnetar, suggesting an FRB emission mechanism that is analogous to radio pulsars despite a huge luminosity difference between two types of objects.