Satellite observations of Bremsstrahlung from widespread energetic electron precipitation events

Abstract

This is a preliminary report of the first satellite observations that have been made of the intensities and energy spectra of the bremsstrahlung >50 keV produced in the atmosphere by intense widespread precipitations of energetic electrons from the outer radiation belt. The measurements afford the opportunity to investigate nearly simultaneously the energetic electron behavior on a worldwide scale during magnetic disturbances. With such a technique, one may study different features of the precipitation processes than those covered by satellite-borne particle detectors, which can provide more detailed particle information in a local region but without simultaneous measurements from many satellites can provide worldwide particle precipitation information only from long-term statistical studies. The observations are made with a 50-cm³ Ge(Li) gamma ray spectrometer that was launched aboard the spin-stabilized satellite 1972–076B into a nearly circular polar orbit at 750-km altitude on October 2, 1972. Correlative measurements of precipitating electrons are also made with an energetic electron spectrometer on board the same satellite. The longitude and hence local time extents of the precipitations are derived by least square fitting techniques from the gamma ray spectrometer responses at various spin angle orientations and satellite locations. The observations indicate the occurrence of nearly simultaneous precipitations over a wide range of local times. Significant variations occur in the intensity versus local time, but in the limited number of cases studied to date the intensities near noon are generally greater than those in the early morning hours.