Search for high-energy electron sources with Polar Patrol Balloon

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We have observed cosmic-ray electrons from 10GeV to 1TeV with the PPB-BETS by a long duration balloon flight using Polar Patrol Balloon(PPB) in Antarctica. The observation was carried out for 13 days at an altitude of 35km in January 2004. The PPB-BETS detector is an imaging calorimeter composed of scintillating-fiber belts and plastic scintillators inserted between lead plates. The geometrical factor of detector is about 600 cm^2sr and the total thickness of lead absorber is 9 radiation lengths. New telemetry system using a commercial satellite of Iridium, power supply by solar batteries, and automatic level control using CPU have successfully been developed and operated during the flight. We have collected 5700 events over 100GeV including nearly 100 candidates of cosmic-ray electrons. In this study, we derived the energy spectrum of cosmic-ray electrons above 100GeV at the top of atmosphere. The energy spectrum with the PPB-BETS agrees well with the extrapolated spectrum of the BETS at 100GeV, and is consistent with that of the emulsion chambers within statistical errors in the 100GeV-1TeV region. We have also observed atmospheric gamma rays from 100GeV to 1TeV with PPB-BETS. Since atmospheric gamma rays at high altitude are mainly produced by a single interaction of primary cosmic rays with atmospheric nuclei, they are very useful to study nuclear interaction models and atmospheric neutrinos. The number of observed atmospheric gamma rays is neargy 100 events in the energy range of 100GeV to 1TeV. We also derived atmospheric gamma-ray spectrum in the energy range of 100GeV to 1TeV with PPB-BETS at an altitude of 35km.