Effects of primary electron transit times on power spectra of auroral-zone X-ray microbursts

Abstract

Changes in structures within bouncing bursts of energetic (≳30 keV) electrons due to velocity dispersion have been estimated. Theoretical calculations show that power spectra of electron intensity fluctuations at ionospheric heights are increasingly damped with increasing frequencies relative to their source spectra. This damping depends strongly on the distance travelled by the electron burst from the burst source region to the ionosphere, but is only weakly dependent on the electron energy spectra. A similar dependence is also found for the ratio between power spectra of electron fluxes above two different threshold energies. These calculations are compared with the observed relative damping rates in power spectra of auroral-zone X-ray microbursts which are caused by bursts of precipitating electrons. On the basis of this comparison it is inferred that the source region of the individual electron bursts is located between the ionosphere and the equator, but probably well off the equatorial plane. The typical fine-structures within X-ray microbursts with frequencies above ~2 Hz are apparently generated quite close to the ionosphere.