The ISS-based Calorimetric Electron Telescope (CALET) is directly measuring the energy spectrum of electron+positron cosmic rays up to 20 TeV. Annihilation or decay of dark matter (DM) could produce signatures in the positron and electron cosmic-ray spectra, thus the parameter space of DM candidate models can be probed by studying these messengers. The TeV-region extension of the spectrum provided by CALET is especially important for heavy DM search, since the signature’s location in energy is closely correlated with the DM mass.The magnet spectrometer AMS-02 on the other hand provides an exclusive positron-only spectrum below the TeV range. The combined analysis of both data-sets allows for DM search with a sophisticated modeling of the astrophysical background, comprising pulsars as the primary positron source and supernova remnant (SNR) sources providing the majority of the electron flux, in addition to a secondary component. As a refinement over a phenomenological power-law parametrization of the background, overlapping individual point source spectra are used as background for deriving limits on DM annihilation and decay from the CALET all-electron and the AMS-02 positron-only data. The used SNR and pulsar samples combine known nearby sources dominating the spectrum at high energies with randomly generated ones throughout the galaxy. By analyzing a large number of samples with also randomized emission spectra parameters, the expected variability of the background is taken into account, improving the reliability of the obtained limits on DM annihilation cross-section and lifetime.

The CALorimetric Electron Telescope (CALET) has been collecting data on the International Space Station for more than seven years since October 2015. CALET is an all-calorimetric instrument with a total vertical thickness of 30 radiation lengths and fine imaging capability, optimized for the measurement of the electron and positron (all-electron) spectrum well into the TeV energy region. The observed event statistics have increased more than three times since its last publication about the all-electron spectrum to 4.8 TeV in 2018. Based on Monte Carlo simulations, the data analysis effectively rejects background protons, resulting in less than 10% contamination up to the TeV region. The expected systematic errors are investigated. The significance of the cutoff at the TeV region in the energy spectrum, which is expected as a result of radiation loss during propagation, has increased to over 6$\sigma$. By observing the detailed structure in the TeV region of the energy spectrum, we will investigate on the presence of possible nearby cosmic-ray sources. In this paper, we will present the updated all-electron spectrum, and briefly discuss its interpretations.

The Calorimetric Electron Telescope (CALET) is a deep electromagnetic calorimeter designed for the measurement of cosmic-ray electrons on the International Space Station. Deployed on the Exposed Facility of the Japanese Experiment Module since August 2015, it observes cosmic-ray electrons with energies up to above 10 TeV and hadrons up to PeV total energies. It is also sensitive to gamma rays in the energy range from 1 GeV to 1 TeV. At energies above 100 GeV, sensitivity is lost in the gamma-ray selection as previously defined. This is due in large part to the contamination of the charge measurement in the CHD (Charge Detector) and the IMC (Imaging Calorimeter) by backscattered particles from the electromagnetic shower in the TASC (Total Absorption Calorimeter). In this work, we implement a revision to the photon selection criteria using a significantly increased simulated dataset, increasing CALET’s exposure at these energies significantly. Furthermore, the allowable geometry for incident photons is expanded and the energy reconstruction revised to tighten the energy resolution for highly inclined tracks. We validate the distributions used for the selection through comparison with real data, evaluate the changes to the instrument response functions, and assess the implications for the flight data analysis of gamma rays with CALET.

The Calorimetric Electron Telescope (CALET) is a deep electromagnetic calorimeter designed for the measurement of cosmic-ray electrons on the International Space Station. Deployed on the Exposed Facility of the Japanese Experiment Module since August 2015, it observes cosmic-ray electrons with energies up to above 10 TeV and hadrons up to PeV total energies. Above a few TeV, the decrease in the electron flux and increased contamination by protons in the boosted decision tree (BDT) selection introduce challenges to determination of the flux at the highest energies and the search for signatures of nearby accelerators. To address the proton contamination, we apply a dedicated event-by-event analysis to evaluate the likelihood of each candidate event being a real electron or a contaminating proton. In this work, we detail the implementation of the likelihood analysis based on physically motivated shower parameters in the CALET calorimeter. Large simulated electron and proton datasets tailored to the parameters of the observed candidate events are generated and studied to produce a likelihood parameter for the improved rejection of protons. The results are tied to the BDT selection in the flight data analysis and summarized for the currently identified candidate events. Finally, we discuss an expansion of this work presently under development to use BDTs trained specifically for each candidate to provide an additional figure of merit.

The International Space Station (ISS) provides an orbital platform for astrophysical missions with lower resource requirements than free-flying satellites. The many uses of the ISS, how7 keVever, can produce unique challenges to the accurate analysis of the data acquired by these instruments. In this work, we present effects observed by the Calorimetric Electron Telescope (CALET), an astroparticle physics mission installed on the Japanese Experiment Module Exposed Facility of the ISS. The CALET calorimeter is sensitive to cosmic-ray electrons and gamma rays from 1 GeV up to above 10 TeV, and to cosmic-ray hadrons up to PeV total energies. The CALET Gamma-ray Burst Monitor (CGBM) is sensitive to X-rays and low-energy gamma rays from 7 keV to 20 MeV. Furthermore, ultra-heavy galactic cosmic-ray (UHGCRs) abundances are measured by CALET using a much more open geometry than is possible for events which shower in the instrument. In this work, we discuss ISS-related issues that affect the observations by CALET. Here we detail the ways these effects are accounted for in the production of scientific results. Finally, the possible impact on future missions such as TIGERISS (Trans-Iron Galactic Element Recorder for the International Space Station; planned for deployment to the ISS in 2026) and mitigation strategies are discussed.

The CALorimetric Electron Telescope (CALET), launched to the ISS in August 2015 and in continuous operation since, measures cosmic-ray (CR) electrons, nuclei, and gamma rays. CALET, with its 27 radiation length deep Total Absorption Calorimeter (TASC), measures particle energy, allowing for the determination of spectra and secondary to primary ratios of the more abundant CR nuclei through 28 Ni, while the main charge detector (CHD) can measure Ultra-Heavy (UH) CR nuclei through 40 Zr. Previous CALET UHGCR analyses used a special high duty cycle ( ∼ 90%) UH trigger that does not require passage through the TASC and used time-and position-dependent detector response corrections based on 14 Si and 26 Fe and an angle-dependent geomagnetic cutoff rigidity selection to show abundances of even nuclei in agreement with SuperTIGER and ACE-CRIS. The work shown here further improves upon those results by restricting UH events to those that pass through both the TASC and CHD. While this constraint does reduce the number of events to ∼ 1/6 of the original UH trigger analysis, the loss of statistics is compensated by improvements in event selection from an energy-binned charge determination and minimum deposited energy that substitutes for the previous minimum geomagnetic rigidity selection. The results shown here represent 7 years of observation for the abundances of elements from Z=10 to Z=40 relative to 26 Fe and are compared to previous measurements from ACE-CRIS, SuperTIGER, and HEAO-3.

The CALorimetric Electron Telescope (CALET) has successfully been carrying out cosmic-ray observations on the International Space Station since October, 2015. 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. The scientific operations are implemented by taking into account orbital variations of geomagnetic rigidity cutoff. Scheduled command sequences are used to control the CALET observation modes on orbit. The high-energy (> 10 GeV) trigger mode is always active for maintaining maximum exposure to high-energy electrons and other high-energy shower events. Also, around the ISS 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. As of June 30, 2023, the total observation time is 2818 days with a live time fraction of the total time around 86 %. Nearly 1.86 billion events are collected with the high-energy trigger.

CALET, the Calorimetric Electron Telescope, launched to the International Space Station in August 2015 and in continuous operation since, has gathered over seven years of data so far. CALET is able to measure cosmic-ray (CR) electrons, nuclei, and gamma rays and with its 27 radiation length deep Total Absorption Calorimeter (TASC), measures particle energy, allowing for the determination of spectra and secondary to primary ratios of the more abundant CR nuclei through $_{28}$Ni, while the main charge detector (CHD) can measure Ultra-Heavy (UH) CR nuclei through $_{40}$Zr. CALET UHCR analyses use a special high duty cycle UH trigger with an expanded geometry that does not require passage through the TASC. To effectively analyze UHCR trigger events, a number of screens and corrections have been developed for the analysis. From time- and position-dependent detector response corrections based on $_{14}$Si and $_{26}$Fe, to an angle-dependent geomagnetic cutoff rigidity selections and minimum deposited energy screens, a number of methods have been explored to optimize UH statistics to varying effect. In this work, we aim to show how these event selection screens and corrections have been developed, how the rigidity screens shown previously by Rauch et al compare to the newer TASC methodology shown in our other ICRC paper, and how TASC selections may be used to influence analysis on the full UH-trigger dataset.

The latest LIGO/Virgo/KAGRA observing run (O4) started on May 24 in 2023. Many ground and space instruments have participated in follow-up observation and search for electromagnetic counterparts of gravitational waves. Calorimetric Electron Telescope (CALET) on the Interna- tional Space Station has also searched for electromagnetic counterparts since the observation started in October 2015. Although CALET is a payload for direct measurement of high-energy cosmic rays, CALET has the capability to observe high-energy gamma-rays above 1 GeV with the Calorimeter (CAL) and X-rays / gamma rays in the energy range from 7 keV to 20 MeV with the CALET Gamma-ray Burst Monitor (CGBM). We searched for electromagnetic counterparts of gravitational wave events in the last LIGO/Virgo observing run (O3). Although no candidate was found in CALET data in O3, CAL and CGBM estimated upper limits of gamma-ray / X-ray flux for the gravitational waves in O3. We have been searching for electromagnetic counterparts of gravitational waves in O4 with improved and automated analysis pipelines to deal with many events with high event rates. As of the end of June 2023, the LIGO/Virgo/KAGRA collaboration reported 169 events via the GCN/LVC NOTICE, and 15 of 169 events were reported to GCN Circulars as significant events. Although CGBM and CAL searched for signals associated with the significant events, no candidates were found around the event time of the significant events. We obtained CAL upper limits for eight significant events of which localization high probability region overlapped with the CAL field of view.

In this work, we present a feasibility study aiming at an enhanced statistical precision of CR helium flux with CALET data. It is based on a wider acceptance with respect to the present fiducial one while ensuring a correct identification of charged particles crossing the detector within much wider geometrical configurations. The expected statistical enhancement for the all-acceptance configuration is nearly 2× with respect to the previous analysis, over the entire energy range (from tens of GeV, up to hundreds of TeV). Preliminary assessment of efficiencies and background sources has been carried out based on energy-dependent charge selections.

We present the measurement of the energy spectrum of the boron flux in cosmic rays based on the data collected by the CALorimetric Electron Telescope (CALET) during 7.25 years of operation on the International Space Station. The energy spectrum is measured from 8.4 GeV/n to 3.8 TeV/n with an all calorimetric instrument with a total thickness corresponding to 1.3 nuclear interaction length and equipped with charge detectors capable of single element resolution. The observed boron flux shows a spectral hardening at the same transition energy E0 ~200 GeV/n of the carbon and oxygen spectra, though B flux has a different energy dependence with respect to C and O. Within the limitations of our data's present statistical significance, the boron spectral index change is found to be slightly larger than that of carbon and oxygen, which are similar. A corresponding break in the energy dependence of the B/C and B/O flux ratios also supports the idea that the secondary cosmic rays exhibit a stronger hardening than primary ones. Moreover, interpreting our data with a Leaky Box model, we argue that the trend of the energy dependence of the B/C and B/O ratios in the TeV/n region could suggest a possible presence of a residual propagation path length, compatible with the hypothesis that a fraction of secondary B nuclei can be produced near the cosmic-ray source.

The study of flux ratios of cosmic-ray primary elements is of particular interest not only to assess the relative abundance of each element, but also to gain a deeper understanding of their propagation in the galaxy. High energy cosmic ray data are the best candidate for this purpose as convection, nuclear decay, and energy degradation can be neglected during their propagation. CALET on the International Space Station has been measuring the flux of several primary elements from proton to nickel for 7 years to date. In this contribution, the flux ratios of heavy primary elements to lighter primaries will be shown, extending the energy range already investigated by previous measurements.

We present the solar modulation of electrons and protons observed by the CALorimetric Electron Telescope onboard the International Space Station for about 7 years since October 2015, during the transition phase from the descending phase of the 24th solar cycle to the ascending phase of the 25th solar cycle. The observed variations of electron and proton count rates at an identical average rigidity of 3.8 GV show a clear charge-sign dependence of the solar modulation of galactic cosmic rays (GCRs), which is reproduced by a numerical drift model of the GCR transport in the heliosphere. It is also found that the ratio of 3.8 GV proton count rate to the neutron monitor count rate in the ascending phase of the 25th solar cycle is clearly different from that in the descending phase of the 24th solar cycle. Correlations between the electron (proton) count rate and the heliospheric environmental parameters, such as the current sheet tilt angle, obtained in this study would be useful for developing an appropriate numerical model of solar modulation for reproducing the observation.

The CALorimetric Electron Telescope (CALET) cosmic ray detector on the International Space Station (ISS) has been in operation since its launch in 2015. The main instrument, the CALorimeter (CAL), is optimized to observe high-energy electrons up to TeV energies, but its three-storied, composite and thick detector enable us to discriminate gamma rays from overwhelming background of charged cosmic rays. Thus, it is monitoring the gamma ray sky from 1 GeV up to 10 TeV with a field of view of about 2 sr, but the exposure is somewhat non-uniform because of the limitation imposed by the inclination angle (51.6 degree) of the ISS orbit. In this paper we report results from gamma ray observations obtained during its mission for more than seven years with increased statistics compared with previous reports. They include properties of the Galactic diffuse gamma rays, spectra of bright Galactic point sources, and light curves of extragalactic active galactic nuclei, which show good consistencies with Fermi-LAT observations of which energy range overlaps with CALET.

The CALET Calorimeter on the International Space Station(ISS) has previously measured the flux and spectrum of iron cosmic-ray nuclei above 10 GeV/n. In order to extend the measurement to the region below 10 GeV/n, we carry out an analysis to utilize the geomagnetic effect. Cutoff rigidities of cosmic-ray nuclei are calculated for all directions for each observation point in the ISS orbit. The integral spectrum of observed rigidities is then obtained by counting the number of iron nuclei in each bin of cutoff rigidity. The absolute flux and differential spectrum are then calculated by taking the detection efficiencies into account. Here we present the details of the analysis procedure and the iron spectrum below 10 GeV/n.

The Calorimetric Electron Telescope (CALET) is a cosmic-ray observatory operating since October 2015 onboard the International Space Station (ISS). The data processed since the beginning of the mission has made it possible to measure with high precision the inclusive flux of cosmic electrons and positrons (all-electron) in the multi-TeV region. The appearance of any structures in this energy region can potentially be connected to the presence of nearby astrophysical sources or dark matter. The CALET detector, consisting of a charge detector, an imaging calorimeter and a total absorption calorimeter has a total vertical thickness of about 30 radiation lengths. The construction characteristics of the instrument allow to obtain an energy resolution better than 2% for electrons and a proton rejection power of about $10^5$. However, the exploration of the multi-TeV region involves dealing with a limited statistical sample and a large proton background. As a consequence, a complex multivariate analysis based on variables connected to the shower development has been adopted. In this contribution, we summarize the results of a study conducted on different multivariate analysis techniques in order to optimize the proton rejection at high energies in the all-electron flux measurement. In particular, we discuss the features of the different methods, the tuning of their parameters and the overall strategy to increase the separation between electrons and protons, avoiding the phenomenon of overfitting.

A precise measurement of the cosmic-ray proton spectrum is carried out with the Calorimetric Electron Telescope (CALET) and a sharp softening of the energy spectrum above 10 TeV is observed. CALET, located on the International Space Station, has started data taking in October 2015 and has accumulated data for more than seven years without any serious troubles. CALET is pursuing the direct measurement of the main components of high energy cosmic rays up to ~1 PeV in order to understand the cosmic ray acceleration and propagation. Thanks to the thick calorimeter that corresponds to 30 radiation lengths and to \sim1.3 proton interaction lengths, the proton analysis presented in this paper spans a broad energy range from 50 GeV to 60 TeV. Proton energy resolution is 30-40%, and the residual background is less than 10% in the E < 10 TeV region. In the multi-TeV region, we observed a spectral softening with a spectral index change from -2.6 to -2.9 in addition to the spectral hardening we had previously confirmed with a high significance above a few hundred GeV. The transition to the softer regime is much sharper than the smooth onset of hardening observed at lower energy.

The ISS-based Calorimetric Electron Telescope (CALET) is directly measuring the energy spectrum of electron+positron cosmic rays up to 20 TeV. Supernova remnants (SNR) are the most likely astrophysical sources to provide the majority of the electron flux, out of which a few nearby young SNR like Vela are expected to dominate in the TeV-region with potentially detectable spectral signatures. Another expected contribution to the spectrum is from pulsars as a primary positron-electron pair source for explanation of the positron excess. Complementary to the CALET all-electron spectrum, the positron-only spectrum measured by the magnet spectrometer AMS-02 below the TeV range provides detailed information on this component. An interpretation of the CALET and AMS-02 data by overlapping spectra from individual pulsar and SNR point sources is presented, combining sources known from electromagnetic wave observations with further randomly generated ones spread throughout the Galaxy. Based on the study of a large number of samples with randomized source locations and emission spectra parameters, best fitting ranges and constraints for these parameters, as well as predictions for the spectrum beyond the so far measured energy range have been derived.

The study of the spectral behavior of heavy cosmic-ray elements may shed light on the details of propagation and acceleration phenomena in our Galaxy. The CALorimetric Electron Telescope (CALET) is measuring the spectra of heavy nuclei up to the highest directly observed energies on the International Space Station. In this contribution, based on the data collected during 7 years of operation, the measurement of the energy dependence of iron and nickel fluxes is presented. With respect to our previous published measurements, the analysis has been extended to a data sample enriched with more than 2.5 (1.5) extra years for iron (nickel). The results of the new analysis are reported together with a detailed assessment of systematic uncertainties. In the energy range explored so far, both spectra show a similar shape and energy dependence, suggesting that iron and nickel may follow almost identical acceleration and propagation mechanisms

The Calorimetric Electron Telescope (CALET), launched to the International Space Station in 2015, provides more than 7 years of continuous observation of the radiation environment at low earth orbit. Using this dataset, we present a method for the detection and categorization of MeV relativistic electron precipitation (REP) events. From this catalog we identify a subset of a few hundred REP events observed at times where CALET is in magnetic conjunction with the Van Allen probes. These conjugate measurements enable studies of associated plasma wave data from RBSPA/B and potential drivers for MeV electron precipitation. We show that roughly 10 percent of the observed REP events are associated with enhanced electromagnetic ion cyclotron wave activity, suggesting that waves can play a significant role in driving MeV electron precipitation.