An excitation mechanism of electromagnetic pulses by relativistic electrons in the brown dwarfs rarefied magnetosphere
A beam pulsed amplifier mechanism responsible for effective amplification of short electromagnetic pulses by relativistic electrons is proposed. Effective pulse amplification inside the rarefied magnetosphere is considered. A conditional growth rate of short electromagnetic pulses is calculated. The amplification takes place for an extraordinary mode in a frequency band close to half the local electron cyclotron frequency. The obtained results based on the conditional instability concept can explain some important features of the radio emissions typical for brown dwarfs, such as the high brightness temperature of its source, circular polarization with handedness switching, periodicity with a period of rotation of the object, and narrow beams of radiation. The proposed mechanism of radio-emission excitation is effective without strong anisotropy of the relativistic electrons distribution function.