SPECTRAL PROPERTIES OF ELECTRON CYCLOTRON MASER EMISSION

G.D.Fleishman

The dependences of the spectral bandwidth of various wave-modes on the parameters of the fast electron distribution function are studied in detail. The natural spectral bandwidth of the ECM peaks is shown to vary significantly as fast electron distribution function parameters and viewing angle change. This agrees well with observations, since solar radio spikes are known to display rather large scatter of the spectral bandwidth of the emission lines both within one event and from one event to another. Typical values of the spectral bandwidth, $\\Delta\\omega/\\omega \\sim 0.1-0.4 \\%$, are found to be consistent with observations of minimum spike bandwidth.

Magnetic irregularities with a broad distribution over scales are shown to provide considerable spectral broadening that is not necessarily small compared with the natural bandwidth even for small magnetic inhomogeneities. The developed re-normalization scheme allows to describe quantitatively the spectral shape of the emission line when the broadening is large.

Moreover, the presence of stronger magnetic inhomogeneities gives rise to splitting of the emission line in two lines in agreement with observed non-integer harmonic ratio between spectrally separated spike bands.

Typical values of the spectral bandwidth are found to be pretty consistent with spike observations. The developed theory suggests new possibilities of the random magnetic field diagnostics. The estimated magnitudes of the random magnetic field at the spike source look rather reasonable.