Leptons with E > 200 MeV trapped in the Earth's radiation belts

Abstract

[1] 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 describe the observed under-cutoff lepton fluxes outside the region of the South Atlantic Anomaly. The separation in quasi-trapped, long-lifetime (O(10 s)), and albedo, short-lifetime (O(100 ms)), components is explained in terms of the drift shell populations observed by AMS. A significantly higher relative abundance of positrons with respect to electrons is seen in the quasi-trapped population. The flux maps as a function of the canonical adiabatic variables L, a 0 are presented for the interval 0.95 < L < 3, 0°< a 0 < 90°f or electrons (E < 10 GeV) and positrons (E < 3 GeV). The results are compared to existing data at lower energies. The properties of the observed under-cutoff particles are also investigated in terms of their residence times and geographical origin.

Leptons with energy >200 MeV trapped near the South Atlantic Anomaly

“…We reported previously the results for the QT component outside the SAA in the work of Fiandrini et al [2002] in which the region B < 0.26 G was completely excluded and no ST particles were observed.…”

“…The pitch angle is preferred to B m since it is limited to 0°/90°. A three-dimensional grid (E, L, a 0 ) is defined to build flux maps as in the work of Fiandrini et al [2002].…”

“…oma.be/spenvis) with a realistic magnetic field model, including both the internal and the external contributions (IGRF, available at http://nssdc.gsfc.nasa.gov/space/model/ models/igrf.html) [Tsyganenko, 1982]; details can be found in the work of Fiandrini et al [2002] and G. Esposito (Study of cosmic ray fluxes in low earth orbit observed with the AMS experiment, http://ams.pg.infn.it/Tesi/Tesi.html, 2002). The AMS Field of View (FoV) along the orbits in the SAA is shown in Figure 2.…”

“…[11] To reject the primary component of the measured lepton fluxes, the lepton trajectories in the Earth's magnetic field were traced in a realistic geomagnetic field model with the Earth's penumbra effects taken into account [Fiandrini et al, 2002] (G. Esposito, http://ams.pg.infn.it/Tesi/ Tesi.html, 2002). Particles are classified as cosmic if they reach a distance of 30 Earth radii.…”

“…The AMS data collected outside the SAA have been analyzed and compared with lower-energy measurements taken at similar altitudes [Fiandrini et al, 2002]. In this paper, we use the high statistics data sample collected by the AMS experiment for a detailed study of the high-energy (O(1 GeV)) lepton fluxes nearby the SAA region, excluded in the previous publication.…”