Fast Radio Bursts from Reconnection in a Magnetar Magnetosphere

The nearly 100% linear polarization has been reported for a few fast radio bursts (FRBs). This finding places severe limits on the emission mechanism. I argue that the completely polarized radiation could be generated in the course of relativistic magnetic reconnection in the outer magnetosphere of the magnetar. At the onset of the magnetar flare, a large-scale magnetic perturbation forms a magnetic pulse, which propagates from the flare cite outward. The pulse strongly compresses magnetospheric plasma and pushes it away. The high-frequency MHD waves are generated when the magnetic pulse reaches the current sheet separating, just beyond the light cylinder, the oppositely directed magnetic fields. Coalescence of magnetic islands in the reconnecting current sheet produces magnetosonic waves, which propagate away on the top of the magnetic pulse and escape in the far zone of the wind as radio waves polarized along the rotational axis of the magnetar. I estimate parameters of the outgoing radiation and show that they are compatible with the observed properties of FRBs.