Electromagnetic fireworks: Fast radio bursts from rapid reconnection in the compressed magnetar wind

Extragalactic fast radio bursts may be produced during magnetic reconnection in a compressed current sheet of the magnetar wind, triggered by the strong fast magnetosonic pulse produced by a magnetar flare. The current sheet is fragmented into a self-similar chain of magnetic islands and the coherent radiation is produced by time-dependent plasma currents at their interfaces during coalescence. We investigate this scenario using 2D radiative relativistic particle-in-cell simulations. We compute the efficiency of the coherent emission and obtain scalings for its peak frequency. Consistent with expectations, a fraction of the incident magnetic flux, scaling with the reconnection rate, is reconnected and converted into fireworks of high-frequency fast waves with an efficiency factor f~0.002. In agreement with previous analytical estimates, we find that fast magnetosonic pulses can trigger relatively narrow-band GHz emission with radio luminosities sufficient to explain extragalactic fast radio bursts. The mechanism also provides a natural explanation for the nanosecond sub-structure recently detected in FRB 20200120E.