Escape of fast radio bursts from magnetars

Fast radio bursts (FRBs) are bright extragalactic transients likely produced by magnetars. We study the propagation of FRBs in magnetar winds, assuming that the wind is strongly magnetized and composed of electron-positron pairs. We focused on the regime where the strength parameter of the radio wave, a_{0, is larger than unity and the wave frequency, ω0, is larger than the Larmor frequency in the background magnetic field, ωL. We show that strong radio waves with a0 > 1 are able to propagate when ω0 > a0ωL, as the plasma current is a linear function of the wave electric field. The dispersion relation is independent of the wave strength parameter when ω0 > a0ωL. Radio waves could instead be damped when ω0 < a0ωL, as a significant fraction of the wave energy is used to compress the plasma and amplify the background magnetic field. Our results suggest that FRBs should be produced at large distances from the magnetar (i.e., R > 10^{12 cm, where the condition ω0 > a0ωL is satisfied). Alternatively, the structure of the magnetar wind should be strongly modified during a flare to allow for the escape of FRBs produced at radii R < 1012 cm.}}