LEPTONS WITH E > 200 MEV TRAPPED IN THE SOUTH ATLANTIC ANOMALY

Abstract

For the first time accurate measurements of electron and positron fluxes in the energy range 0.2 ÷ 10 GeV have been performed with the Alpha Magnetic Spectrometer (AMS) at altitudes of 370 ÷ 390 km in the geographic latitude interval ±51.7°. We focused on the under-cutoff lepton fluxes inside the region of the South Atlantic Anomaly (SAA), defined as region where the local magnetic field B ≤ 0.26 G. A clear transtion region from stably-trapped flux typical of the lnner Van Allen Belts to quasi-trapped flux typical underneath the Van Allen Belts is observed in the SAA up to energies O(Gev). The observations strongly support positrons abundance in the Inner Van Allen Belts, both in the stably trapped component and in the quasi-trapped one. The flux maps as a function of the canonical adiabatic variables L, αo are presented for the intervval 0.95 < L < 3, 0° < αo < 90° for electrons (E < 10 GeV) and positrons (E < 3 GeV). The results are compared with existing data at lower energies.