Balloon observations of X rays in the auroral zone II

Data from a long-duration balloon flight at 35-km height over the auroral zone during August 1959 showed that only very small fluxes of energetic X rays accompany visible auroras at this latitude. The maximum observed photon flux above 25 kev during a bright aurora was 2.5 cm−2 sec−1. Much larger fluxes, up to 40 cm−2 sec−1, preceded two active visible displays by about half an hour. On August 17 and 18 X-ray influxes were observed for several hours during the daytime. From Explorer VI data these are believed to be associated with the filling-up of the outer radiation belt after a geomagnetic storm. The scintillation counter employed permitted a determination of the X-ray energy spectrum at 6 g cm−2 depth from 25 to 300 kev on this and several other flights. From an analysis given here the parent electron spectrum is derived and found to be extremely steep. Typically, the ratio of the differential photon intensity at 30 kev to that at 160 kev is 350 to 1. Other balloon flights during August 1959 show that a large loss of electrons having energy >25 kev is occurring even on magnetically rather quiet days.