Photon Acceleration in Magnetized Plasma: A Mechanism for Fast Radio Bursts

We propose a mechanism for fast radio bursts based on photon acceleration by relativistic shocks propagating through highly magnetized electron--positron plasmas, as expected in magnetar magnetospheres. Density modulations at the shock front create relativistically moving refractive-index perturbations that transform low-frequency electromagnetic precursors into amplified high-frequency radiation. We show that the predicted frequencies, durations, and energetics of the resulting fast radio bursts are consistent with the magnetic-field strengths, shock Lorentz factors, and characteristic spatial scales expected in magnetar magnetospheres.