Abstract

The CALorimetric Electron Telescope (CALET) on the International Space Station consists of a high-energy cosmic-ray CALorimeter (CAL) and a lower-energy CALET Gamma-ray Burst Monitor (CGBM). CAL is sensitive to electrons up to 20 TeV, cosmic-ray nuclei from Z = 1 through Z ∼ 40, and gamma rays over the range 1 GeV–10 TeV. CGBM observes gamma rays from 7 keV to 20 MeV. The combined CAL-CGBM instrument has conducted a search for gamma-ray bursts (GRBs) since 2015 October. We report here on the results of a search for X-ray/gamma-ray counterparts to gravitational-wave events reported during the LIGO/Virgo observing run O3. No events have been detected that pass all acceptance criteria. We describe the components, performance, and triggering algorithms of the CGBM—the two Hard X-ray Monitors consisting of LaBr₃(Ce) scintillators sensitive to 7 keV–1 MeV gamma rays and a Soft Gamma-ray Monitor BGO scintillator sensitive to 40 keV–20 MeV—and the high-energy CAL consisting of a charge detection module, imaging calorimeter, and the fully active total absorption calorimeter. The analysis procedure is described and upper limits to the time-averaged fluxes are presented.

The Calorimetric Electron Telescope (CALET) was launched on the International Space Station in 2015 and since then has collected a large sample of cosmic-ray charged particles over a wide energy. Thanks to a couple of layers of segmented plastic scintillators placed on top of the detector, the instrument is able to identify the charge of individual elements from proton to iron (and above). The imaging tungsten scintillating fiber calorimeter provides accurate particle tracking and the lead tungstate homogeneous calorimeter can measured the energy with a wide dynamic range. One of the CALET scientific objectives is to measure the energy spectra of cosmic rays to shed light on their acceleration and propagation in the Galaxy. By the observation in first five years, a precise measurement of the iron spectrum is now available in the range of kinetic energy per nucleon from 10 GeV/n to 2 TeV/n. The CALET's result with a description of the analysis and details on systematic uncertainties will be illustrated. Also, a comparison with previous experiments' results is given.

The relative abundance of cosmic ray nickel nuclei with respect to iron is by far larger than for all other transiron elements; therefore it provides a favorable opportunity for a low background measurement of its spectrum. Since nickel, as well as iron, is one of the most stable nuclei, the nickel energy spectrum and its relative abundance with respect to iron provide important information to estimate the abundances at the cosmic ray source and to model the Galactic propagation of heavy nuclei. However, only a few direct measurements of cosmic-ray nickel at energy larger than ∼3 GeV/n are available at present in the literature, and they are affected by strong limitations in both energy reach and statistics. In this Letter, we present a measurement of the differential energy spectrum of nickel in the energy range from 8.8 to 240 GeV/n, carried out with unprecedented precision by the Calorimetric Electron Telescope (CALET) in operation on the International Space Station since 2015. The CALET instrument can identify individual nuclear species via a measurement of their electric charge with a dynamic range extending far beyond iron (up to atomic number Z=40). The particle's energy is measured by a homogeneous calorimeter (1.2 proton interaction lengths, 27 radiation lengths) preceded by a thin imaging section (3 radiation lengths) providing tracking and energy sampling. This Letter follows our previous measurement of the iron spectrum [1O. Adriani (CALET Collaboration), Phys. Rev. Lett. 126, 241101 (2021).PRLTAO0031-900710.1103/PhysRevLett.126.241101], and it extends our investigation on the energy dependence of the spectral index of heavy elements. It reports the analysis of nickel data collected from November 2015 to May 2021 and a detailed assessment of the systematic uncertainties. In the region from 20 to 240 GeV/n our present data are compatible within the errors with a single power law with spectral index -2.51±0.07.

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Focusing on the electron and positron spectrum measured with the Calorimetric Electron Telescope (CALET), which shows characteristic structures, we calculate the flux contributions of cosmic rays that have escaped from randomly appearing supernova remnants. We adopt a Monte Carlo method to take into account the stochastic nature of the appearance of nearby sources. We find that without a complicated energy dependence of the diffusion coefficient, simple power-law diffusion coefficients can produce spectra similar to the CALET spectrum, even with a dispersion in the injection index. The positron component measured with AMS-02 is consistent with a bump-like structure around 300 GeV in the CALET spectrum. One to three nearby supernovae can contribute up to a few tens of percent of the CALET flux at 2–4 TeV, while ten or more unknown and distant (≳500 pc) supernovae account for the remaining several tens of percent of the flux. The CALET spectrum, showing a sharp drop at ∼1 TeV, allows for a contribution of cosmic rays from an extraordinary event that occurred ∼400 kyr ago. This type of event releases electrons/positrons with a total energy more than 10 times the average energy for usual supernovae, and its occurrence rate is lower than one three-hundredth of the usual supernova rate.

The CALorimetric Electron Telescope CALET is collecting science data on the International Space Station since October 2015 with excellent and continuous performance. Energy is measured with a deep homogeneous calorimeter (1.2 nuclear interaction lengths, 27 radiation lengths) preceded by an imaging pre-shower (3 radiation lengths, 1mm granularity) providing tracking and 10-5 electron/proton discrimination. Two independent sub-systems identify the charge Z of the incident particle from proton to iron and above (Z<40). CALET measures the cosmic-ray electron + positron flux up to 20 TeV, gamma rays up to 10 TeV, and nuclei up to the PeV scale. In this paper, we report the on-orbit performance of the instrument and summarize the main results obtained during the first 5 years of operation, including the electron + positron energy spectrum and the individual spectra of protons, heavier nuclei and iron. Solar modulation and gamma-ray observations are also concisely reported, as well as transient phenomena and the search for gravitational wave counterparts.

The Calorimetric Electron Telescope (CALET), in operation on the International Space Station since 2015, collected a large sample of cosmic-ray iron over a wide energy interval. In this Letter a measurement of the iron spectrum is presented in the range of kinetic energy per nucleon from 10 GeV/n to 2.0 TeV/n allowing the inclusion of iron in the list of elements studied with unprecedented precision by space-borne instruments. The measurement is based on observations carried out from January 2016 to May 2020. The CALET instrument can identify individual nuclear species via a measurement of their electric charge with a dynamic range extending far beyond iron (up to atomic number Z=40). The energy is measured by a homogeneous calorimeter with a total equivalent thickness of 1.2 proton interaction lengths preceded by a thin (3 radiation lengths) imaging section providing tracking and energy sampling. The analysis of the data and the detailed assessment of systematic uncertainties are described and results are compared with the findings of previous experiments. The observed differential spectrum is consistent within the errors with previous experiments. In the region from 50 GeV/n to 2 TeV/n our present data are compatible with a single power law with spectral index -2.60±0.03.

In this paper, we present the measurement of the energy spectra of carbon and oxygen in cosmic rays based on observations with the Calorimetric Electron Telescope on the International Space Station from October 2015 to October 2019. Analysis, including the detailed assessment of systematic uncertainties, and results are reported. The energy spectra are measured in kinetic energy per nucleon from 10 GeV/n to 2.2 TeV/n with an all-calorimetric instrument with a total thickness corresponding to 1.3 nuclear interaction length. The observed carbon and oxygen fluxes show a spectral index change of ∼0.15 around 200 GeV/n established with a significance >3σ. They have the same energy dependence with a constant C/O flux ratio 0.911±0.006 above 25 GeV/n. The spectral hardening is consistent with that measured by AMS-02, but the absolute normalization of the flux is about 27% lower, though in agreement with observations from previous experiments including the PAMELA spectrometer and the calorimetric balloon-borne experiment CREAM.

The CALorimetric Electron Telescope CALET is a space instrument designed to carry out precision measurements of high energy cosmic-rays on the JEM-EF external platform on the International Space Station, where it has been collecting science data continuously since mid October 2015. In addition to its primary goal of identifying nearby sources of high-energy electrons and possible signatures of dark matter in the electron spectrum, CALET is carrying out extensive measurements of the energy spectra, relative abundances and secondary-to-primary ratios of elements from proton to iron, and even above (up to Z = 40), studying the details of galactic particle propagation and acceleration. An overview of CALET based on the data taken during the first three years of observations is presented, including a direct measurement of the electron+positron energy spectrum from 11 GeV to 4.8 TeV. The proton spectrum has been measured from 50 GeV to 10 TeV covering, for the first time with a single space-borne instrument, the whole energy interval previously investigated in separate sub-ranges by magnetic spectrometers and calorimetric instruments. Preliminary spectra of cosmic-ray nuclei are also presented, together with gamma-ray observations and searches for an e.m. counterpart of LIGO/Virgo GW events.

The CALET (CALorimetric Electron Telescope) space experiment, which is currently conducting direct cosmic-ray observations onboard the International Space Station (ISS), is an all-calorimetric instrument optimized for cosmic-ray electron measurements with capability to measure hadrons and gamma-rays. Since the start of observation in October 2015, smooth and continuous operations have taken place. In this paper, we will give a brief summary of the CALET observations ranging from charged cosmic rays, gamma-rays, to space weather, while focusing on the energy spectra of electrons and protons.

© 2019 authors. In this paper, we present the analysis and results of a direct measurement of the cosmic-ray proton spectrum with the CALET instrument onboard the International Space Station, including the detailed assessment of systematic uncertainties. The observation period used in this analysis is from October 13, 2015 to August 31, 2018 (1054 days). We have achieved the very wide energy range necessary to carry out measurements of the spectrum from 50 GeV to 10 TeV covering, for the first time in space, with a single instrument the whole energy interval previously investigated in most cases in separate subranges by magnetic spectrometers (BESS-TeV, PAMELA, and AMS-02) and calorimetric instruments (ATIC, CREAM, and NUCLEON). The observed spectrum is consistent with AMS-02 but extends to nearly an order of magnitude higher energy, showing a very smooth transition of the power-law spectral index from-2.81±0.03 (50-500 GeV) neglecting solar modulation effects (or-2.87±0.06 including solar modulation effects in the lower energy region) to-2.56±0.04 (1-10 TeV), thereby confirming the existence of spectral hardening and providing evidence of a deviation from a single power law by more than 3σ.

CALorimetric Electron Telescope (CALET) has been accumulating data of high-energy cosmic rays on the International Space Station since August 2015. In addition to the primary observation of the all-electron spectra, CALET also measures the spectra of nuclei, their relative abundances and secondary-to-primary ratios to the highest energy region ever directly observed in order to investigate details of their origin and propagation in the galaxy. The CALET instrument consists of two layers of segmented plastic scintillators to identify the individual elements from Z = 1 to 40, a 3 radiation length thick tungsten-scintillating fiber imaging calorimeter to obtain complementary charge and tracking information, and a 27 radiation length thick segmented PWO calorimeter to measure the energy. In this paper, the capability of CALET to perform nuclei measurements and preliminary energy spectra of heavy nuclei components using 962 days of data is presented.

The CALorimetric Electron Telescope (CALET) installed on the International Space Station has multiple event trigger modes for measuring high-energy particles and gamma rays. The observations of the low-energy cosmic-ray (CR) electrons (electrons + positrons) in an energy region from 1 GeV to 10 GeV have been successfully performed by a low-energy shower trigger mode working in the geomagnetic polar regions. The continuous measurements of the low-energy CR electrons may provide a crucial key to the understanding of the solar modulation of the galactic cosmic rays. Here we have analyzed the low-energy CR electrons measured by CALET over the past three years to investigate the solar modulation of the CR electrons. We have obtained the continuous variation of the low-energy electron flux increasing as time passes, which have been expected from a recent weakening solar cycle. We have also confirmed that there are additional small fluctuations in the flux, that has a potential to be explained by the effects of the interplanetary coronal mass ejections or the co-rotating interaction region of the solar wind.

The CALorimetric Electron Telescope primary detector (CALET-CAL) is a 30 radiation-length-deep hybrid calorimeter designed for the accurate measurement of high-energy cosmic rays. It is capable of triggering on and giving near complete containment of electromagnetic showers from primary electrons and gamma rays from 1 GeV to over 10 TeV. The first 24 months of on-orbit scientific data (2015 November 01-2017 October 31) provide valuable characterization of the performance of the calorimeter based on analyses of the gamma-ray data set in general and bright point sources in particular. We describe the gamma-ray analysis, the expected performance of the calorimeter based on Monte Carlo simulations, the agreement of the flight data with the simulated results, and the outlook for long-term gamma-ray observations with the CAL.

© 2018. The American Astronomical Society. All rights reserved. We present the results of searches for gamma-ray counterparts of the LIGO/Virgo gravitational wave events using CALorimetric Electron Telescope (CALET) observations. The main instrument of CALET, CALorimeter (CAL), observes gamma-rays from ∼1 GeV up to 10 TeV with a field of view (FOV) of nearly 2 sr. In addition, the CALET gamma-ray burst monitor views ∼3 sr and ∼2π sr of the sky in the 7 keV-1 MeV and the 40 keV-20 MeV bands, respectively, by using two different crystal scintillators. The CALET observations on the International Space Station started in 2015 October, and here we report analyses of events associated with the following gravitational wave events: GW151226, GW170104, GW170608, GW170814, and GW170817. Although only upper limits on gamma-ray emission are obtained, they correspond to a luminosity of 1049 ∼ 1053 erg s-1 in the GeV energy band depending on the distance and the assumed time duration of each event, which is approximately on the order of luminosity of typical short gamma-ray bursts. This implies that there will be a favorable opportunity to detect high-energy gamma-ray emission in further observations if additional gravitational wave events with favorable geometry will occur within our FOV. We also show the sensitivity of CALET for gamma-ray transient events, which is on the order of 10-7 erg cm-2 s-1 for an observation of 100 s in duration.

© 2018 Elsevier B.V. The CALorimetric Electron Telescope (CALET), launched for installation on the International Space Station (ISS) in August, 2015, has been accumulating scientific data since October, 2015. CALET is intended to perform long-duration observations of high-energy cosmic rays onboard the ISS. CALET directly measures the cosmic-ray electron spectrum in the energy range of 1 GeV to 20 TeV with a 2% energy resolution above 30 GeV. In addition, the instrument can measure the spectrum of gamma rays well into the TeV range, and the spectra of protons and nuclei up to a PeV. In order to operate the CALET onboard ISS, JAXA Ground Support Equipment (JAXA-GSE) and the Waseda CALET Operations Center (WCOC) have been established at JAXA and Waseda University, respectively. Scientific operations using CALET are planned at WCOC, taking into account orbital variations of geomagnetic rigidity cutoff. Scheduled command sequences are used to control the CALET observation modes on orbit. Calibration data acquisition by, for example, recording pedestal and penetrating particle events, a low-energy electron trigger mode operating at high geomagnetic latitude, a low-energy gamma-ray trigger mode operating at low geomagnetic latitude, and an ultra heavy trigger mode, are scheduled around the ISS orbit while maintaining maximum exposure to high-energy electrons and other high-energy shower events by always having the high-energy trigger mode active. The WCOC also prepares and distributes CALET flight data to collaborators in Italy and the United States. As of August 31, 2017, the total observation time is 689 days with a live time fraction of the total time of ∼ 84%. Nearly 450 million events are collected with a high-energy (E > 10 GeV) trigger. In addition, calibration data acquisition and low-energy trigger modes, as well as an ultra-heavy trigger mode, are consistently scheduled around the ISS orbit. By combining all operation modes with the excellent-quality on-orbit data collected thus far, it is expected that a five-year observation period will provide a wealth of new and interesting results.

© 2018 American Physical Society. Extended results on the cosmic-ray electron + positron spectrum from 11 GeV to 4.8 TeV are presented based on observations with the Calorimetric Electron Telescope (CALET) on the International Space Station utilizing the data up to November 2017. The analysis uses the full detector acceptance at high energies, approximately doubling the statistics compared to the previous result. CALET is an all-calorimetric instrument with a total thickness of 30 X0 at normal incidence and fine imaging capability, designed to achieve large proton rejection and excellent energy resolution well into the TeV energy region. The observed energy spectrum in the region below 1 TeV shows good agreement with Alpha Magnetic Spectrometer (AMS-02) data. In the energy region below ∼300 GeV, CALET's spectral index is found to be consistent with the AMS-02, Fermi Large Area Telescope (Fermi-LAT), and Dark Matter Particle Explorer (DAMPE), while from 300 to 600 GeV the spectrum is significantly softer than the spectra from the latter two experiments. The absolute flux of CALET is consistent with other experiments at around a few tens of GeV. However, it is lower than those of DAMPE and Fermi-LAT with the difference increasing up to several hundred GeV. The observed energy spectrum above ∼1 TeV suggests a flux suppression consistent within the errors with the results of DAMPE, while CALET does not observe any significant evidence for a narrow spectral feature in the energy region around 1.4 TeV. Our measured all-electron flux, including statistical errors and a detailed breakdown of the systematic errors, is tabulated in the Supplemental Material in order to allow more refined spectral analyses based on our data.

© 2017 Published by the American Physical Society. First results of a cosmic-ray electron and positron spectrum from 10 GeV to 3 TeV is presented based upon observations with the CALET instrument on the International Space Station starting in October, 2015. Nearly a half million electron and positron events are included in the analysis. CALET is an all-calorimetric instrument with total vertical thickness of 30 X0 and a fine imaging capability designed to achieve a large proton rejection and excellent energy resolution well into the TeV energy region. The observed energy spectrum over 30 GeV can be fit with a single power law with a spectral index of -3.152±0.016 (stat+syst). Possible structure observed above 100 GeV requires further investigation with increased statistics and refined data analysis.

The charge detector (CHD) of the Calorimetric Electron Telescope (CALET) on board the International Space Station (ISS) has a huge geometric factor for detecting MeV electrons and is sensitive to relativistic electron precipitation (REP) events. During the first 4 months, CALET CHD observed REP events mainly at the dusk to midnight sector near the plasmapause, where the trapped radiation belt electrons can be efficiently scattered by electromagnetic ion cyclotron (EMIC) waves. Here we show that interesting 5-20 s periodicity regularly exists during the REP events at ISS, which is useful to diagnose the wave-particle interactions associated with the nonlinear wave growth of EMIC-triggered emissions.

The CALorimetric Electron Telescope (CALET) is a space experiment, currently under development by Japan in collaboration with Italy and the United States, which will measure the flux of cosmic-ray electrons (and positrons) up to 20 TeV energy, of gamma rays up to 10 TeV, of nuclei with Z from 1 to 40 up to 1 PeV energy, and will detect gamma-ray bursts in the 7 keV to 20 MeV energy range during a 5 year mission. These measurements are essential to investigate possible nearby astrophysical sources of high energy electrons, study the details of galactic particle propagation and search for dark matter signatures. The main detector of CALET, the Calorimeter, consists of a module to identify the particle charge, followed by a thin imaging calorimeter (3 radiation lengths) with tungsten plates interleaving scintillating fibre planes, and a thick energy measuring calorimeter (27 radiation lengths) composed of lead tungstate logs. The Calorimeter has the depth, imaging capabilities and energy resolution necessary for excellent separation between hadrons, electrons and gamma rays. The instrument is currently being prepared for launch (expected in 2015) to the International Space Station ISS, for installation on the Japanese Experiment Module - Exposure Facility (JEM-EF).

The Calorimetric Electron Telescope (CALET) is a space experiment, currently under development by Japan in collaboration with Italy and the United States. CALET will measure the flux of cosmic ray electrons (including positrons) up to 20 TeV, gamma-rays up to 10 TeV and nuclei from Z = 1 up to 40 up to 1000 TeV during a two-year mission on the International Space Station (ISS), extendable to five years. The unique feature of CALET is its thick, fully active calorimeter that allows measurements well into the TeV energy region with excellent energy resolution (&lt; 3%), coupled with a fine imaging upper calorimeter to accurately identify the starting point of electromagnetic showers. For continuous high performance of the detector, it is required to calibrate each detector component on orbit. We use the measured response to minimum ionizing particles for the energy calibration, taking data in a dedicated trigger mode and selecting useful events in off-line analysis. In this paper, we present on-orbit and off-line data handling methods for the energy calibration developed through beam tests at CERN-SPS and Monte Carlo simulations. (C) 2015 COSPAR. Published by Elsevier Ltd. All rights reserved.

The CALorimetric Electron Telescope (CALET) is a space experiment, currently under development by Japan in collaboration with Italy and the United States, which will measure the flux of cosmic-ray electrons (and positrons) up to 20 TeV energy, of gamma rays up to 10 TeV, of nuclei with Z from 1 to 40 up to 1 PeV energy, and will detect gamma-ray bursts in the 7 keV to 20 MeV energy range during a 5 year mission. These measurements are essential to investigate possible nearby astrophysical sources of high energy electrons, study the details of galactic particle propagation and search for dark matter signatures. The main detector of CALET, the Calorimeter, consists of a module to identify the particle charge, followed by a thin imaging calorimeter (3 radiation lengths) with tungsten plates interleaving scintillating fibre planes, and a thick energy measuring calorimeter (27 radiation lengths) composed of lead tungstate logs. The Calorimeter has the depth, imaging capabilities and energy resolution necessary for excellent separation between hadrons, electrons and gamma rays. The instrument is currently being prepared for launch (expected in 2015) to the International Space Station ISS, for installation on the Japanese Experiment Module - Exposure Facility (JEM-EF).

CALET (CALorimetric Electron Telescope) is a high energy cosmic-ray detector to be installed on International Space Station in 2015 to carry out accurate measurements of high energy electrons and gamma-rays. For verification of the detector performance, we carried out balloon experiments using CALET prototype detectors in May 2006 (bCALET-1) and in August 2009 (bCALET-2). In this paper we mainly report about the second experiment using bCALET-2. bCALET-2 is a calorimetric instrument composed of a 3.58 radiation length thick tungsten-scintillating fiber imaging calorimeter (IMC) and a 13.4 radiation length thick bismuth germanium-oxide calorimeter (TASC). The concept of the structure is similar to that of CALET, but the number of sensors and the thickness of materials were optimized for the balloon experiment. The observation was carried out at the Taiki Aerospace Research Field of JAXA in Hokkaido, and the detector was flown successfully for 2.5 h at a level altitude of 35 km. The observed events were analyzed by methods developed through Monte Carlo simulations, and the energy spectra of electrons and atmospheric gamma-rays in the energy range of 1-30 GeV were obtained and compared to the results of previous experiments. (C) 2014 COSPAR. Published by Elsevier Ltd. All rights reserved.

The Calorimetric Electron Telescope (CALET) is a new space experiment for astroparticle physics, which will carry out a five-year observation at the Japanese Experiment Module-Exposed Facility (JEM-EF) of the International Space Station (ISS). The experiment, currently under development by Japan in collaboration with Italy and the United States, will measure mainly 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 1000 TeV. We have carried out a beam test of the CALET calorimeter at CERN-SPS by using the Beam-Test Model (BTM), which consisted of the Structure and Thermal Model (STM) and the Bread Board Model(BBM) of the front end circuits. The model consists of the same support structure as the CALET flight model and it includes the Imaging Calorimeter (IMC), the Total Absorption Calorimeter(TASC) and the Charge Detector(CHD). A part of the sensors; the scintillating fibers in the IMC, the PWO logs in the TASC, and the plastic scintillators paddles in the CHD, was adapted for the test. We will describe the model, and will report the basic performance obtained in the beam test.

We report on the measurements performed with relativistic ions from Be to Fe, at the Fragment Separator (FRS) of the GSI Helmholtzzentrum fur Schwerionenforschung in Darmstadt, to test the performance of charge-sensitive detectors that were designed to separate - via multiple dE/dx measurements - fully stripped nuclei of cosmic origin in the experiment CALET. The latter is a space mission by the Japanese Space Agency (JAXA) scheduled to be launched to the International Space Station (ISS) in 2013. The CALET instrument is managed by an international collaboration and it is scheduled to take data for 5 years on the Exposure Facility (JEM-EF) of the Japanese module KIBO on the ISS.
The aim of the test was to accurately measure the response of the scintillator to different nuclear species and parametrize the saturation of the scintillation light in order to assess the impact of this effect on the charge resolution of the instrument. (C) 2011 Elsevier B.V. All rights reserved.

We are developing the CALET mission to observe high energy cosmic rays at the Japanese Experiment Module/Exposed Facility (JEM/EF) on the International Space Station. The instrument will be flown in 2013, and will be used for 5 years. The primary scientific purpose of CALET is to search for nearby cosmic ray sources and dark matter. We carried out an accelerator beam test with high energy particles with the CALET prototype at the CERN-SPS. The purpose of this test was to assess the detector performance as well as to study the accuracy of the Monte Carlo simulation method. The prototype detector consists of an imaging calorimeter with 256 scintillating fibers and a total absorption calorimeter consisting of 16 PWO logs. The longitudinal structure is similar with the CALET instrument. We used positron and proton beams in the energy region from 6 to 200 GeV, and from 30 to 150 GeV, respectively. Comparing the experimental data with the simulation results, we have measured the energy deposition in each component, the energy resolution, the lateral shower spread and the e/p separation capability.

Calorimetric Electron Telescope (CALET) will be a high energy cosmic ray observatory on the Japanese Experimental Module - Exposed Facility of the International Space Station. In addition to electrons and gamma-rays, CALET has an excellent detection capability of cosmic ray nuclei. In order to determine the atomic number of measured nuclei, the CHarge Detector (CHD) is placed on the top of the calorimeter. The CALET-CHD consists of two orthogonal layers of plastic scintillator charge-measuring modules. Each layer is segmented into 14 scintillator paddles (45 cm×3.2 cm×1 cm) for the reduction of back scattering effects. We evaluated the charge resolution of the plastic scintillators with heavy ion accelerators. In this presentation, we will report the design of the CALET-CHD and its nuclei identification capability as inferred from heavy ion beam tests.

The CALorimetric Electron Telescope, CALET, is a mission to study high energy phenomena in the universe by observing high energy cosmic rays (electrons, gamma rays, and nuclei) on the International Space Station. The instrument consists of a segmented plastic scintillator charge-measuring module, an imaging calorimeter consisting of 8 scintillating fiber planes interleaved with tungsten plates of 3 radiation length, and a total absorption calorimeter consisting of orthogonal PWO logs of 27 radiation length. It is necessary to eliminate the background events, mostly low energy protons that prevent efficient observation of high energy cosmic rays. Therefore, CALET has an on-board trigger system to select events which are 1) high energy showers, 2) low energy showers and 3) non-interacting protons or heavy nuclei. These triggers are generated by a combination of the signals from the charge detector, the imaging calorimeter, and the top layer of PWO in the total absorption calorimeter. A CERN-SPS beam test of the CALET prototype detector was carried out by using muons, electrons, and hadrons. We introduce the CALET trigger system and present its performance verified during the beam test.

We carried out the balloon experiments using CALET (CALorimetric Electron Telescope) prototype detectors in May 2006 (bCALET-1) and August 2009 (bCALET-2) for verification of both the detector performance and the capability of measuring the cosmic rays at higher atmosphere. The bCALET-2 instrument for observing the electrons and the gamma rays at energies in 1-100 GeV is composed of an imaging calorimeter consisting of 4096 scintillating fibers with a total of 3.6 radiation lengths of tungsten plates, and a total absorption calorimeter consisting of crossed 60 BGO logs with a total of 13.4 radiation lengths depth. The bCALET-2 was launched from the Taiki Aerospace Research Field, Japan Aerospace Exploration Agency, in Hokkaido, and flew successfully for 2.5 hours at a level altitude of 35 km. In this paper, we will present the spectra of electrons and gamma rays in the energy range of 1-100 GeV measured by bCALET-2, comparing with our previous observations, bCALET-1 and BETS. The detector performance is studied by comparing with the simulations, and the observed fluxes are found to be compatible with the expected.

The CALorimetric Electron Telescope, CALET, is a versatile detector for exploring the high energy universe, planned to be placed on the Japanese Experiment Module Facility of the International Space Station, ISS. CALET is designed to perform direct measurements of electrons from 1 GeV to 20 TeV, gamma-rays from 10 GeV to 10 TeV, and protons and nuclei from several 10 GeV to 1000 TeV. The main detector consists of a Charge Detector (CHD), an Imaging Calorimeter (IMC), and a Total Absorption Calorimeter (TASC). The total thickness of the calorimeter is 30 X0 for electromagnetic particles or 1.3 λ for protons. We have been carrying out Monte Carlo simulations with EPICS to study the CALET performance. With its imaging and deep calorimeter, CALET provides excellent proton rejection, ∼ 105, and a high energy resolution, ∼2%, over 100 GeV for electromagnetic particles, which make possible the observation of electrons and gamma-rays into the TeV region. In this paper, we will present the expected performance in observing the different particle species, including the geometric factor, the trigger efficiency, the energy resolution and the particle identification power.

The CALET payload will be installed in the Japanese Experiment Module Exposed Facility (JEM-EF) of the International Space Station (ISS). We developed a balloon-borne payload to evaluate the performance of CALET by carrying out precursor flights for the electron and gamma-ray observations. The first flight of bCALET-1 (balloon-borne CALET prototype) was carried out in 2006, and the enhanced version, bCALET-2, was successfully flown in August 2009. The bCALET-2 is composed of IMaging Calorimeter (IMC) and Total AbSorption Calorimeter (TASC). The IMC has an area of 256 mm × 256 mm, and is consisted of 8 layers of scintillating fiber belts with a total 3.6 radiation lengths of tungsten plates interleaved within the fiber planes for imaging the pre-shower development. TASC is consisted of crossed BGO logs (25 mm × 25 mm × 300 mm in each) with a total of 13.4 radiation lengths depth, for measuring the total energy deposit of incoming shower particles. The geometry factor is nearly 320 cm2sr over 10 GeV. We succeeded the observation of the electron energy spectrum in 1 GeV ∼ several 10 GeV electron and the atmospheric gamma-rays in 1 GeV ∼ a few 10 GeV, which are consistent with previous observations by BETS. The results are compared with simulations for confirming the detector performance.

We carried out a balloon observation of cosmic rays with a prototype of the CALET (bCALET-1) at the Sanriku Balloon Center of the Japan Aerospace Exploration Agency. The main purpose of the experiment was verification of the CALET. The detector consists of 1024 scintillating fibers for precise imaging and 24 BGO scintillator for total absorption of showers. The observation was carried at an altitude between 35 and 37 km for about 3.5 hours. We measured electrons in the energy region between 1 to 10 GeV. The prototype system was verified in the balloon environment. We have obtained the electron flux which is useful to investigate solar modulation. In combination with the flux between 10 to 100GeV measured by BETS, rigidity cutoff effect was clearly observed. These results showed good agreement with that of our Monte-Carlo simulation and demonstrated the detection capability of the CALET in the enegy region below 10 GeV. Now we are planning a series of balloon experiments with larger-scale detectors and longer-duration flights, which include one-month observation by a super-pressure balloon. © 2009 The Physical Society of Japan.