Abstract
The CALorimetric Electron Telescope (CALET) space experiment, which has been developed by Japan in collaboration with Italy and the United States, is a high-energy astroparticle physics mission on the International Space Station (ISS). The primary goals of the CALET mission include investigation of possible nearby sources of high-energy electrons, detailed study of galactic cosmic-ray acceleration and propagation, and search for dark matter signatures. With a long-term observation onboard the ISS, the CALET experiment measures the flux of cosmic-ray electrons (including positrons) up to 20 TeV, gamma-rays to 10 TeV, and nuclei up to 1,000 TeV based on its charge separation capability from Z = 1 to 40. Since the start of science operation in mid-October, 2015, a continuous observation has been maintained without any major interruptions. The number of triggered events over 10 GeV is nearly 20 million per month. By using the data obtained during the first two-years, here we present a summary of the CALET observations: 1) Electron+positron energy spectrum, 2) Nuclei analysis, 3) Gamma-ray observation with a characterization of the on-orbit performance. The search results for the electromagnetic counterparts of LIGO/Virgo gravitational wave events are also discussed.
Highlights
The CALorimetric Electron Telescope (CALET) [1, 2], which has been developed by Japan in collaboration with Italy and the United States, is a high-energy astroparticle physics experiment installed on the International Space Station (ISS)
As sharp structures in the spectrum may be blurred by binning effects, we studied them by shifting the energy binning and confirmed that such effects are negligible compared to our estimated systematic uncertainties [5]
CALET was successfully launched on Aug. 19, 2015, and the detector has been continuously very stable since Oct. 13, 2015
Summary
The CALorimetric Electron Telescope (CALET) [1, 2], which has been developed by Japan in collaboration with Italy and the United States, is a high-energy astroparticle physics experiment installed on the International Space Station (ISS). Several unique and important characteristics, as briefly mentioned in the Introduction These include its ability to resolve in detail the initial development of showers, as well as tracks generated by non-interacting minimum ionizing particles (MIPs), and its capacity to precisely measure the energy of electrons in the TeV region as a result of its depth of 30 X0. Since the TASC absorbs the majority of the energy (∼95%) contained in an electromagnetic cascade, well into the TeV region, CALET is able to measure the primary energies of cosmic ray electrons and gamma rays with very small corrections. In principle, this should result in precise energy measurements with low systematic errors. This clearly demonstrates CALET’s capability to observe cosmic rays over a very wide dynamic range
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