Electron–cyclotron maser observable modes

We investigate wave amplification through the electron–cyclotron maser mechanism. We calculate absorption and emission coefficients without any approximations, also taking into account absorption by the ambient thermal plasma. A power‐law energy distribution for the fast electrons is used, as indicated by X‐ray and microwave observations. We develop a model for the saturation length and amplification ratio of the maser, scan a large parameter space and calculate the absorption and emission coefficients for every frequency and angle. Previous studies concluded that the unobservable Z mode dominates in the ν p ≈ ν B region, and that millisecond spikes are produced in the region ν p ν B <0.25. We find that the observable O and X modes can produce emission in the 0.8< ν p ν B <2 region, which is expected at the footpoints of a flaring magnetic loop. The important criterion for observability is the saturation length and not the growth rate, as was assumed previously, and, even when the Z mode is the most strongly amplified, less strongly amplified O or X modes are still intense enough to be observed. The brightness temperature computed with our model for the saturation length is found to be of order 10 16  K and higher. The emission is usually at a frequency of 2.06 ν B , and at angles of 30°–60° to the magnetic field. The rise time of the amplified emission to maximum is a few tenths of a millisecond to a few milliseconds, and the emission persists for as long as new fast electrons arrive in the maser region.