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

TL;DR

This study presents the final results of cosmic-ray electron observations from 30 GeV to 3 TeV using balloon-borne emulsion chambers, revealing a power-law spectrum and implications for nearby sources within 1 kpc.

Contribution

It provides the comprehensive cosmic-ray electron spectrum up to 3 TeV based on extensive balloon experiments and calibration, enhancing understanding of cosmic-ray propagation and sources.

Findings

Electron spectrum follows a power-law with index -3.28±0.10.

Evidence of electrons up to 3 TeV indicates nearby sources within 1 kpc.

Results support diffusive propagation models for cosmic-ray electrons.

Abstract

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.