Experimental investigation of short-term periodicities in the quiet-time X-ray flux at mid-latitudes

Balloon observations of the X-ray flux of photons with energies greater than 20 keV, measured at an atmospheric depth of 8 g cm[raised -2] in the vicinity of Seattle, Washington, (L = 2.7) were analyzed. The randomness of time interval t required to receive each four counts was tested using a modified duration-distribution law. The technique of power spectral analysis was used to investigate periodicities in the flux. Statistically significant peaks were found in the spectral power density of this high altitude X-ray data, although neither pulsation nor microburst phenomena were present. Count rates based on different time intervals were used to investigate the periodic nature of the flux. The peaks were found in the X-ray power spectra at periods corresponding to the bounce periods of electrons in the energy range 20 to 400 keV. This observation indicates that the observed X-ray fluxes at L = 2.7 were influenced by trapped electrons in the magnetosphere on this L shell.