92 research outputs found
Re-appearance of antiferromagnetic ordering with Zn and Ni substitution in La_{2-x}Sr_xCuO_4
The effects of nonmagnetic Zn and magnetic Ni substitution for Cu site on
magnetism are studied by measurements of uniform magnetic susceptibility for
lightly doped La_{2-x}Sr_xCu_{1-z}M_zO_4 (M=Zn or Ni) polycrystalline samples.
For the parent x=0, Zn doping suppresses the N\'{e}el temperature T_N whereas
Ni doping hardly changes T_N up to z=0.3. For the lightly doped samples with
T_N~0, the Ni doping recovers T_N. For the superconducting samples, the Ni
doping induces the superconductivity-to-antiferromagnetic transition (or
crossover). All the heavily Ni doped samples indicate a spin glass behavior at
\~15 K.Comment: 2 pages including 3 figures, to be published in Physica C (LT23,
Hiroshima 2002
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 the knee in the energy spectrum of cosmic rays
The knee in the all-particle energy spectrum is scrutinized with a
phenomenological model, named poly-gonato model, linking results from direct
and indirect measurements. For this purpose, recent results from direct and
indirect measurements of cosmic rays in the energy range from 10 GeV up to 1
EeV are examined. The energy spectra of individual elements, as obtained by
direct observations, are extrapolated to high energies using power laws and
compared to all-particle spectra from air shower measurements. A cut-off for
each element proportional to its charge Z is assumed. The model describes the
knee in the all-particle energy spectrum as a result of subsequent cut-offs for
individual elements, starting with the proton component at 4.5 PeV, and the
second change of the spectral index around 0.4 EeV as due to the end of stable
elements (Z=92). The mass composition, extrapolated from direct measurements to
high energies, using the poly-gonato model, is compatible with results from air
shower experiments measuring the electromagnetic, muonic, and hadronic
components. But it disagrees with the mass composition derived from X_max
measurements using Cerenkov and fluorescence light detectors.Comment: 30 pages, 21 figures, 9 tables, accepted by Astroparticle Physic
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 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 3 sr
and 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 erg s 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
~erg\,cm\,s 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)
Energy Spectrum of Cosmic-Ray Electron and Positron from 10 GeV to 3 TeV Observed with the Calorimetric Electron Telescope on the International Space Station
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
CALET UPPER LIMITS on X-RAY and GAMMA-RAY COUNTERPARTS of GW151226
We present upper limits in the hard X-ray and gamma-ray bands at the time of the Laser Interferometer Gravitational-wave Observatory (LIGO) gravitational-wave event GW151226 derived from the CALorimetric Electron Telescope (CALET) observation. The main instrument of CALET, CALorimeter (CAL), observes gamma-rays from ∼1 GeV up to 10 TeV with a field of view of ∼2 sr. The CALET gamma-ray burst monitor (CGBM) 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 scintillator-based instruments. The CGBM covered 32.5% and 49.1% of the GW151226 sky localization probability in the 7 keV-1 MeV and 40 keV-20 MeV bands respectively. We place a 90% upper limit of 2 ×10-7 erg cm-2 s-1 in the 1-100 GeV band where CAL reaches 15% of the integrated LIGO probability (∼1.1 sr). The CGBM 7σ upper limits are 1.0 ×10-6 erg cm-2 s-1 (7-500 keV) and 1.8 ×10-6 erg cm-2 s-1 (50-1000 keV) for a 1 s exposure. Those upper limits correspond to the luminosity of 3-5 ×1049 erg s-1, which is significantly lower than typical short GRBs
Extended Measurement of the Cosmic-Ray Electron and Positron Spectrum from 11 GeV to 4.8 TeV with the Calorimetric Electron Telescope on the International Space Station
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\u27s 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
Energy calibration of CALET onboard the International Space Station
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
- …