Highlights from the CALET observations for 7.5 years on the International Space Station

Abstract

The CALorimetric Electron Telescope (CALET) space experiment is a high-energy astroparticle physics mission installed on the International Space Station (ISS). The primary goals of the CALET mission include studying the details of galactic cosmic-ray acceleration and propagation, and searching for possible nearby sources of high-energy electrons and dark matter signatures. The CALET experiment is measuring the flux of cosmic-ray electrons (including positrons) to 20 TeV, gamma-rays to 10 TeV and nuclei with Z=1 to 40 up to 1,000 TeV. The instrument consists of two layers of segmented plastic scintillators for the identification of cosmic-rays via a measurement of their charge (CHD), a 3 radiation length thick tungsten-scintillating fiber imaging calorimeter (IMC) and a 27 radiation length thick lead-tungstate calorimeter (TASC). The instrument was launched on August 19, 2015 to the ISS and installed on the Japanese Experiment Module-Exposed Facility (JEM-EF). Since the start of operations in mid-October, 2015, CALET has been in continuous observation mode over 7.5 years and mainly triggering on high energy (>10 GeV) cosmic-ray showers without any major interruption. The number of triggered events over 10 GeV is nearly 1.86 billion events as of June 30, 2023. Here, we present the highlights of the CALET latest results, including the electron + positron energy spectrum, the spectra of protons and other nuclei, gamma-ray observations, as well as the characterization of on-orbit performance. Someresults on the electromagnetic counterpart search for LIGO/Virgo gravitational wave events and the observations of solar modulation and gamma-ray bursts are also included.