Satellite X ray mappings of sporadic auroral zone electron precipitation events in the local dusk sector

Simultaneous mappings of bremsstrahlung X ray events from the atmosphere resulting from electron precipitation have been performed from a satellite with an array of collimated cadmium telluride spectrometers. The X ray intensities and energy spectra (> or approx. =21 keV) where measured over contiguous view directions. The satellite, P78-1, was launched into a sun-synchronous noon-midnight orbital at approx.600-km altitude on February 24, 1979, and through its spinning motion with a approx.5.5-s period provides continual scans of the X ray sources below. Data are presented from three sporadic events in which the X ray intensities varied strongly with time. Within each of these events, bursts of approx.(30--100) second duration were observed. Some of the bursts were recorded in three or four sensors, thus setting a lower limit to their spatial extent of several hundred kilometers. Other bursts appeared in only one sensor, thereby restricting the area over which they could have been generated. These bursts of X rays emanated primarily from the dusk sector, a local time region where few balloon X ray measurements have been reported. The X ray fluxes were asymmetric about local dusk, the intensities at earlier times being quite low. During one of the X ray burstsmore » in which the precipitation was confined to a relatively small spatial region it is estimated that the total number of electrons (>21 keV) precipitating into the atmosphere was approx.10/sup 23/ per second.« less