Approaching the knee -- balloon-borne observations of cosmic ray composition

Below the knee in the cosmic ray spectrum, balloon and spacecraft experiments offer the capability of direct composition and energy measurements on the primary particles. A major difficulty is obtaining enough exposure to extend the range of direct measurements sufficiently high in energy to permit overlap with ground-based observations. Presently, balloon and space measurements extend only up to ~100 TeV, well below the range of ground-based experiments. The prospect of Ultra-Long Duration Balloon missions offers the promise of multiple long flights that can build up exposure. The status of balloon measurements to measure the high energy proton and nuclear composition and spectrum is reviewed, and the statistical considerations involved in searching for a steepening in the spectrum are discussed. Given the very steeply falling spectrum, it appears unlikely that balloon experiments will be able to extend the range of direct measurements beyond 1000 TeV any time in the near future. Especially given the recent suggestions from KASCADE that the proton spectrum steepens only at 4000-5000 TeV, the chance of detecting the knee with direct measurements of protons to iron on balloons is not likely to occur without significant increases in the payload and flight duration capabilities of high altitude balloons.Comment: 10 pages, to be published, J. Phys. Conf. Ser. (Proc. Workshop on Physics at the End of the Galactic Cosmic Ray Spectrum, Aspen, April 2005

On-orbit Operations and Offline Data Processing of CALET onboard the ISS

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. 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 approximately 84%. Nearly 450 million events are collected with a high-energy (E>10 GeV) trigger. 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.Comment: 11 pages, 7 figures, published online 27 February 201

Search for GeV Gamma-ray Counterparts of Gravitational Wave Events by CALET

We present results on searches for gamma-ray counterparts of the LIGO/Virgo gravitational-wave events using CALorimetric Electron Telescope ({\sl CALET}) observations. The main instrument of {\sl CALET}, CALorimeter (CAL), observes gamma-rays from $\sim1$ GeV up to 10 TeV with a field of view of nearly 2 sr. In addition, the {\sl CALET} gamma-ray burst monitor (CGBM) views $\sim$3 sr and $\sim2\pi$ 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 {\sl CALET} observations on the International Space Station started in October 2015, 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 $10^{49}\sim10^{53}$ erg s$^{-1}$ in the GeV energy band depending on the distance and the assumed time duration of each event, which is approximately the order of luminosity of typical short gamma-ray bursts. This implies 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 field-of-view. We also show the sensitivity of {\sl CALET} for gamma-ray transient events which is the order of $10^{-7}$~erg\,cm$^{-2}$\,s$^{-1}$ for an observation of 100~s duration.Comment: 12 pages, 8 figures, 1 table. Accepted for publication in Astrophysical Journa

The CALorimetric Electron Telescope (CALET) for high-energy astroparticle physics on the International Space Station

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)

On-orbit operations and offline data processing of CALET onboard the ISS

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 \u3e 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