Measurement of high-energy cosmic-ray electrons with a Polar Patrol Balloon

One of the major purpose of recent cosmic-ray studies is to know the origin, acceleration mechanism and propagation properties inside the Galaxy. Along this line many efforts have been spent to observe a precise spectrum of the electron component of cosmic-rays. The main difficulty to study high-energy electrons is the detection of these electrons. The flux is much lower than the abundant proton component, and we need an observation of long duration and a detector with a high rejection power against the background protons. We propose to carry a newly developed scintillating-fiber detector on the Polar Patrol Balloon (PPB) and to expose it for 30 days. The goal of this observation is to determine a definite electron energy-spectrum ranging from 10 GeV to TeV region based on a high statistical accuracy with a long exposure by the PPB. In the result, we can expect to obtain direct evidence for the origin of high-energy electrons and a precise knowledge of their propagation in the Galaxy including solar modulation effects on the electron flux

Observations of High Energy Cosmic-Ray Electrons from 30 GeV to 3 TeV with Emulsion Chambers

We have performed a series of cosmic-ray electron observations using the balloon-borne emulsion chambers since 1968. While we previously reported the results from subsets of the exposures, the final results of the total exposures up to 2001 are presented here. Our successive experiments have yielded the total exposure of 8.19 m^2 sr day at the altitudes of 4.0 - 9.4 g/cm^2. The performance of the emulsion chambers was examined by accelerator beam tests and Monte-Carlo simulations, and the on-board calibrations were carried out by using the flight data. In this work we present the cosmic-ray electron spectrum in the energy range from 30 GeV to 3 TeV at the top of the atmosphere, which is well represented by a power-law function with an index of -3.28+-0.10. The observed data can be also interpreted in terms of diffusive propagation models. The evidence of cosmic-ray electrons up to 3 TeV suggests the existence of cosmic-ray electron sources at distances within ~1 kpc and times within ~1x10^5 yr ago.Comment: 38 pages, 10 figures, 3 tables, Accepted for publication in Ap

High energy electron observation by Polar Patrol Balloon flight in Antarctica

We accomplished a balloon observation of the high-energy cosmic-ray electrons in 10-1000GeV to reveal the origin and the acceleration mechanism. The observation was carried out for 13 days at an average altitude of 35km by the Polar Patrol Balloon (PPB) around Antarctica in January 2004. The detector is an imaging calorimeter composed of scintillating-fiber belts and plastic scintillation counters sandwiched between lead plates. The geometrical factor is about 600cm^2sr, and the total thickness of lead absorber is 9 radiation lengths. The performance of the detector has been confirmed by a test flight at the Sanriku Balloon Center and by an accelerator beam test using the CERN-SPS (Super Proton Synchrotron at CERN). The new telemetry system using the Iridium satellite, the power system supplied by solar panels and the automatic flight level control operated successfully during the flight. We collected 5.7×10^3 events over 100GeV, and selected the electron candidates by a preliminary data analysis of the shower images. We report here an outline of both detector and observation, and the first result of the electron energy spectrum over 100GeV obtained by an electronic counter

The CALET, CALorimetric Electron Telescope, Mission for the International Space Station

The CALorimetric Electron Telescope, CALET, mission is proposed for the Japanese Experiment Module Exposure Facility of the International Space Station. Major goals of the mission are precise measurements of the electrons in a few GeV - 10 TeV and the gamma-rays in 100 MeV - several TeV, keeping an energy resolution of a few % over 100 GeV. From the measurements, a systematic investigation of high-energy electromagnetic process in universe will be performed. A detector of SUSY particle which is a candidate of the dark matter would also be expected. The detector is composed of an imaging calorimeter of scinillating fibers and a total absorption calorimeter. Total thickness of absorber is 45 r.l for electron-magnetic particles and 2.1 m.f.p for protons. Total weight of the payload is nearly 2,200 kg, and the effective geometrical factor should be ~ 1.0 m2 sr. The hadron rejection power can be 10**6 for electrons