Measurement of low-energy cosmic-ray electron and positron spectra at 1 AU with the AESOP-Lite spectrometer

TL;DR

This paper reports a new measurement of low-energy cosmic-ray electron and positron spectra at 1 AU using the AESOP-Lite balloon spectrometer, providing insights into solar modulation effects and cosmic ray composition.

Contribution

It presents the first detailed spectra of cosmic-ray electrons and positrons in the 20 MeV to 1 GeV range from a balloon flight, including the positron fraction at low energies.

Findings

Positron fraction below 100 MeV appears flat.

The all-electron spectrum aligns with heliospheric transport models.

Data collected during positive solar magnetic polarity epoch.

Abstract

We report on a new measurement of the cosmic ray (CR) electron and positron spectra in the energy range of 20 MeV -- 1 GeV. The data were taken during the first flight of the balloon-borne spectrometer AESOP-Lite (Anti Electron Sub Orbital Payload), which was flown from Esrange, Sweden, to Ellesmere Island, Canada, in May 2018. The instrument accumulated over 130 hours of exposure at an average altitude of 3 g.cm$^{-2}$ of residual atmosphere. The experiment uses a gas Cherenkov detector and a magnetic spectrometer, consisting of a permanent dipole magnet and silicon strip detectors (SSDs), to identify particle type and measure the rigidity. Electrons and positrons were detected against a background of protons and atmospheric secondary particles. The primary cosmic ray spectra of electrons and positrons, as well as the re-entrant albedo fluxes, were extracted between 20 MeV -- 1 GeV during a positive solar magnetic polarity epoch. The positron fraction below 100 MeV appears flat, suggesting diffusion dominated solar modulation at low rigidity. The all-electron spectrum is presented and compared with models from a heliospheric numerical transport code.