Cosmic-Ray Electron Flux from 1GeV to 10 GeV with Low-Energy Trigger in the CALET Experiment
Abstract
The Calorimetric Electron Telescope (CALET) was installed on the International Space Station (ISS) in August 2015 and began to collect data in October 2015. CALET has multiple event trigger modes for measuring high-energy particles and gamma rays, and the effective observations have been successfully performed by scheduling these trigger modes according to the conditions of ISS position and orbital information. The cosmic-ray (CR) electrons (electrons + positrons) in the energy region from 10 GeV to 20 TeV, that may provide a possible signature of high-energy electron acceleration at nearby CR origin, have been measured by using a high-energy shower trigger mode. In addition, a low-energy (LE) shower trigger mode working at the polar region can measure the low-energy CR electrons in an energy range of 1 GeV to 10 GeV. By using this LE shower trigger, stable and continuous observations of the low-energy CR electrons have been accomplished for about 2.5 years that is comparable to one quarter of the period of the solar activity cycle.In this study, we have analyzed flight data obtained by the LE shower trigger for 812 days from October 12, 2015 to December 31, 2017. Using a physics analysis consisting of seven event selections, including a track reconstruction utilizing the Kalman filter method and an electron identification based on the lateral energy-deposit distribution in the TASC first layer with respect to the shower axis, we succeeded to keep electron efficiency of about 50% at 1GeV and that of 70% or more above 2 GeV while removing more than 99% of protons. In this presentation we will show the variations of the energy spectrum of CR electrons in an energy range of 1 GeV to 10 GeV observed by CALET from October 2015 to December 2017, and also discuss the physics implications of the solar modulation of CR electrons.
- Publication:
-
42nd COSPAR Scientific Assembly
- Pub Date:
- July 2018
- Bibcode:
- 2018cosp...42E2308M