Electron beam induced radio emission from ultracool dwarfs

摘要: We present the numerical simulations for an electron-beam-driven and loss-cone-driven electron-cyclotron maser (ECM) with different plasma parameters magnetic field strengths a relatively small region short time-scale in attempt to interpret recent discovered intense radio emission from ultracool dwarfs. find that large amount of electromagnetic energy can be effectively released beam-driven ECM, which rapidly heats surrounding plasma. A developed high-energy tail electrons velocity space (resulting heating process ECM) may produce continuum depending on initial strength external electron beam current. Both significant linear polarization circular waves obtained simulations. The spectral distributions simulated show harmonics appear 10 70$\nu_{\rm pe}$ ($\nu_{\rm is frequency) non-relativistic case 600$\nu_{\rm relativistic case, makes it difficult fundamental cyclotron frequency observed frequencies. wide band should therefore covered by future observations.