In August 2015, the CALorimetric Electron Telescope (CALET), designed for long exposure observations of high energy cosmic rays, docked with the International Space Station (ISS) and shortly ...thereafter began to collect data. CALET will measure the cosmic ray electron spectrum over the energy range of 1 GeV to 20 TeV with a very high resolution of 2% above 100 GeV, based on a dedicated instrument incorporating an exceptionally thick 30 radiation-length calorimeter with both total absorption and imaging (TASC and IMC) units. Each TASC readout channel must be carefully calibrated over the extremely wide dynamic range of CALET that spans six orders of magnitude in order to obtain a degree of calibration accuracy matching the resolution of energy measurements. These calibrations consist of calculating the conversion factors between ADC units and energy deposits, ensuring linearity over each gain range, and providing a seamless transition between neighboring gain ranges. This paper describes these calibration methods in detail, along with the resulting data and associated accuracies. The results presented in this paper show that a sufficient accuracy was achieved for the calibrations of each channel in order to obtain a suitable resolution over the entire dynamic range of the electron spectrum measurement.
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.
Relativistic electron precipitation (REP) is a relatively high‐latitude phenomenon where high‐energy electrons trapped in the outer radiation belt are lost into the Earth’s atmosphere. REP events ...observed at low Earth orbit show varying temporal profiles and global distributions. While the precipitation origin has been attributed to specific wave modes or scattering sources, the sorting of REP events by type or driver remains an unsolved challenge. In this study, we analyze the temporal profile of relativistic electron precipitation events observed by the CALorimetric Electron Telescope (CALET) experiment on board the International Space Station. We use an unsupervised machine learning technique called Self‐Organizing‐Maps (SOM) to automatically detect and then classify relativistic electron events observed by the two scintillator layers at the top of the apparatus, sensitive to electrons with energies >1.5 MeV and >3.4 MeV, respectively. We calculate the power spectral density (PSD) of the count rates observed by both sensors and use them as an input for the SOM. The SOM technique groups the PSDs by their similarity, resulting in a classification of relativistic electron events by the periodicity of the observed precipitation. We investigate the L‐shell and magnetic local time distribution of the resulting classification, and energy spectral index associated with the observations. Clear precipitation patterns are observed and compared to past precipitation categorization attempts as well as known distributions of various scattering mechanisms. The classification reveals features through the sorting of the variability of the rapid precipitation, allowing the identification of different precipitation populations with varying properties.
Plain Language Summary
Fast electrons are normally trapped by the Earth’s magnetic field. However, they often get released in bursts and impact the upper layers of the atmosphere near the poles. The underlying processes are still not well understood and debated. In this study we use an unsupervised artificial intelligence technique called Self‐Organizing‐Maps (SOM) to automatically detect and classify the observations made by a charged particle detector onboard the International Space Station (ISS). The SOM categorizes the bursts based on their variability and group together observations by their similarity. We compare the categorization with the spatial location of the electron bursts. Clear patterns are observed and compared with past categorizations attempts.
Key Points
Relativistic Electron Precipitation (REP) is observed by the CALET experiment from the International Space Station
The Self‐Organizing‐Map technique is used for automatic detection and classification of rapidly varying REP intervals
The Self‐Organizing‐Map distinguish between different REP populations
À l’hiver 1947-1948, Henri Calet, au même titre que d’autres intellectuels métropolitains comme Michel Leiris ou Francis Ponge, est invité à Sidi Madani, au sud d’Alger, afin de débattre de questions ...politiques et culturelles propres à l’Algérie. Cette invitation est aussi pour chacun l’occasion de jouir d’excellentes conditions matérielles pour mener à bien ses propres travaux. L’escapade algérienne de Calet se prolonge par un voyage au Maroc, à caractère plus privé. Au cours de ce séjour, Calet prend des notes, écrit ses impressions, rend compte de ce qu’il voit. Réunis ici, les textes nord-africains de Calet, même sous leur aspect inachevé, sont représentatifs au premier chef de son style, de son humour, de sa faculté aiguë d’observation et, plus encore peut-être, de son inclination, qui sera de plus en plus forte au fil des années, à la notation brève et à l’écriture impressionniste.
En 1935 paraît un livre qui devient très rapidement objet de scandale, il s’agit de La Belle Lurette d’Henri Calet. La voix d’un enfant racontant des adultes trop indifférents aux normes sociales ...dans un milieu populaire suscite des commentaires négatifs d’une part et de l’autre : à gauche, parce que ce menu peuple est trop teinté d’anarchisme, à droite parce qu’est décrit trop crûment la misère humaine dans un pays qui se veut résolument moderne. Et pourtant ce livre publié chez Gallimard connaîtra un bon succès. Puis, Calet disparaîtra dans la nuit des temps de l’époque, à cause de la guerre, bien sûr, et d’autres problèmes liés à la justice, pour réapparaître après dans une alternance de nouvelles disparitions. Ce n’est que grâce au bouche-à-oreille de ses quelques admirateurs que son œuvre, au gré des années, sera republiée. Nous nous proposons d’analyser ce premier roman pour chercher les raisons de cette indécision pérenne du public et des éditeurs alors que sa voix est l’une des plus attachantes du XXe siècle.
The CALorimetric Electron Telescope (CALET) is an imaging calorimeter under construction for launch to the ISS in 2014 for a planned 5year mission. CALET consists of a charge detection module (CHD) ...with two segmented planes of 1cm thick plastic scintillator, an imaging calorimeter (IMC) with a total of 3 radiation lengths (X∘) of tungsten plates read out with 8 planes of interleaved scintillating fibers, and a total absorption calorimeter (TASC) with 27 X∘ of lead tungstate (PWO) logs. The primary objectives of the instrument are to measure electron energy spectra from 1GeV to 20TeV, to detect gamma-rays above 10GeV, and to measure the energy spectra of nuclei from protons through iron up to 1,000TeV. In this paper we describe how the geomagnetic field at the 51.6° inclination orbit of the ISS can be used to allow CALET to measure the rare ultra-heavy (UH) cosmic ray (CR) abundances, which provide important clues for the CR source and acceleration mechanism. The CHD scintillator response is relatively insensitive to energy above minimum ionization, and the angle-dependent rigidity as a function of geomagnetic latitude can be exploited to discriminate particles above this energy threshold. Such events require corrections for trajectory in instrument that can be made with only the top 4 layers of the IMC, which allows for considerably greater geometric acceptance than for events that require passage through the TASC for energy determination. Using this approach CALET will be able to measure UH CR relative abundances over its expected mission with superior statistics to previous space instruments.
The CALorimetric Electron Telescope (CALET) is an imaging calorimeter under construction for launch to the ISS in 2014 for a planned 5year mission. CALET consists of a charge detection module (CHD) ...with two segmented planes of 1cm thick plastic scintillator, an imaging calorimeter (IMC) with a total of 3 radiation lengths (X∘) of tungsten plates read out with 8 planes of interleaved scintillating fibers, and a total absorption calorimeter (TASC) with 27 X∘ of lead tungstate (PWO) logs. The primary objectives of the experiment are to measure the electron e-+e+ energy spectra from 1GeV to 20TeV, to detect gamma-rays above 10GeV, and to measure the energy spectra of nuclei from protons through iron up to 1000TeV. In this paper we describe how the geomagnetic field at the 51.6° inclination orbit of the ISS can be used to allow CALET to measure the distinct electron and positron fluxes. The positron fraction has been seen to rise above ∼10GeV by previous experiments (HEAT, AMS-01), and more recently to continue to increase to higher energies (∼80GeV for PAMELA, ∼200GeV for Fermi and ∼350GeV with the best statistics for AMS-02). Utilizing the geomagnetic cutoff, CALET will be able to distinguish electrons and positrons in the ∼3–20GeV energy range where the positron fraction turns upward to complement existing high statistics measurements.
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