2026ApJ...999L...2Z

Recent observations of long period radio transients, such as GLEAM-X J0704-37 and ILT J1101+5521, have revealed a previously unrecognized population of Galactic radio transient sources associated with white dwarf (WD)-M dwarf (MD) binaries. It is an open question how to produce coherent radio emission in these systems, though a model driven by binary interaction seems likely given the nature and correlation of the emission with the binaries' orbital period. Using kinetic plasma simulations, we demonstrate that the relativistic electron cyclotron maser instability (ECMI) is a viable mechanism for generating radio pulses in WD-MD systems, akin to planetary radio emission, such as that from the Jupiter-Io system. We quantify the relativistic ECMI in the nonlinear regime under conditions relevant for WD radio emission for the first time. Our simulations demonstrate that the ECMI can intrinsically produce partially linearly polarized emission relevant to explaining the observed emission spectra of two Galactic sources, though the precise details will depend on the plasma composition. Our work paves the way for a systematic and fully nonlinear computational modeling of radio emission from interacting WD sources.