2025MNRAS.544.2160L

Non-resonant interactions between Alfvén waves and a relativistic plasma result in the formation of the population inversions necessary for synchrotron maser emission (SME) across a wide range of magnetizations and temperatures. We calculate the peak frequencies of the SME resulting from this interaction and show that the characteristic frequencies and energetics of fast radio bursts (FRBs) can be produced in the relativistic wind of a magnetar using this mechanism. Wind Lorentz factors of $\gamma _w\gtrsim 310$ are shown to be necessary to explain observed FRBs. Emission is possible at temperatures of $\theta = k_bT/mc^2\lesssim 0.02$. We further examine the periods and magnetic fields of the central magnetar and demonstrate that the optimal values of these properties align with the observed magnetar population provided that the magnetosphere is disturbed by the flaring activity. These results allow the properties of the environment such as temperature and magnetization to be probed from the observed FRB frequency and luminosity.