Induced Scattering of Fast Radio Bursts in Magnetar Magnetospheres

We investigate induced Compton/Brillouin scattering of electromagnetic waves in magnetized electron and positron pair plasma by verifying kinetic theory with Particle-in-Cell simulations. Applying this to fast radio bursts (FRBs) in magnetar magnetospheres, we find that the scattering--although suppressed by the magnetic field--inevitably enters the linear growth stage before the incident wave amplitude becomes comparable to the background magnetic field during its outward propagation through the magnetosphere. The subsequent evolution bifurcates: full scattering occurs when the density exceeds a critical value, whereas below it the scattering saturates and the FRB can escape without substantial induced-scattering attenuation. This nonlinear saturation eases the tension with observations of compact emission regions and may explain the observed diversity, including the presence or absence of FRBs associated with X-ray bursts.