Broad-spatial characteristics and energy spectrum characteristics of auroral X-rays observed by a Polar Patrol Balloon

Polar Patrol Balloon (PPB) No.6 experiment was performed over Antarctica, in order to observe wide-area characteristics of bremsstrahlung X-rays radiated from energetic precipitated electrons. PPB No.6 was launched from Syowa Station on 5 January 1993 and flew along one and a half circumpolar paths. Distinct enhancements of auroral X-rays were often observed during the entire flight period of 27 days. This is the first observation of broad-spatial distribution of auroral X-rays by a unique instrument onboard a long life balloon. X-ray enhancements were dominant in the magnetic local dayside, and some small enhancements were observed at low latitude below 60°. Such low latitude enhancements have simple temporal structures similar to plasmaspheric hiss. The harder spectrum events tend to occur in the lower invariant latitudes, except for a few events. Latitudinal dependence of auroral X-ray spectrum agrees with latitudinal dependence of characteristic energy for cyclotron resonance. Diurnal energy variation of the X-ray spectrum was observed. This variation can be explained by theoretical precipitation lifetime on cyclotron resonance. All of the observed facts suggest that energetic electron precipitation is caused by cyclotron resonance