On observations of auroral-zone X-rays with energies up to and greater than 200 keV

Abstract

Balloon measurements of auroral-zone X-rays revealed several precipitation events of electrons with energies up to some hundred keV. These events can be divided in two groups according to their energy spectrum. Events with relatively steep energy spectrum occur during the daytime. Their spectrum can be approximated in an exponential form with characteristic energies well below 50 keV. Nighttime events have a flat energy spectrum, which deviates from an exponential form. In these cases the calculated characteristic energies of exponential fittings over limited energy intervals were generally above 50 keV and a considerable variability of the spectrum was observed. Maximum values of the characteristic energy are often related to maximum changes of intensity, not to maximum intensities. These nighttime events are not related in a unique way to a certain phase of the polar substorm.