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Featured researches published by F. Kakimoto.


Physical Review Letters | 1998

Extension of the cosmic ray energy spectrum beyond the predicted Greisen-Zatsepin-Kuz'min cutoff

M. Takeda; N. Hayashida; Kohei Honda; N. Inoue; K. Kadota; F. Kakimoto; K. Kamata; S. Kawaguchi; Y. Kawasaki; N. Kawasumi; H. Kitamura; E. Kusano; Y. Matsubara; Kazuaki Murakami; M. Nagano; D. Nishikawa; H. Ohoka; N. Sakaki; Makoto Sasaki; K. Shinozaki; N. Souma; M. Teshima; R. Torii; I. Tsushima; Yukio Uchihori; Takashi Yamamoto; Shin’ichirou Yoshida; H. Yoshii

The cosmic-ray energy spectrum above 10^{18.5} eV is reported using the updated data set of the Akeno Giant Air Shower Array (AGASA) from February 1990 to October 1997. The energy spectrum extends beyond 10^{20} eV and the energy gap between the highest energy event and the others is being filled up with recently observed events. The spectral shape suggests the absence of the 2.7 K cutoff in the energy spectrum or a possible presence of a new component beyond the 2.7 K cutoff.


The Astrophysical Journal | 1999

SMALL-SCALE ANISOTROPY OF COSMIC RAYS ABOVE 1019 EV OBSERVED WITH THE AKENO GIANT AIR SHOWER ARRAY

M. Takeda; N. Hayashida; K. Honda; N. Inoue; K. Kadota; F. Kakimoto; K. Kamata; S. Kawaguchi; Y. Kawasaki; N. Kawasumi; E. Kusano; Y. Matsubara; Kazuaki Murakami; M. Nagano; D. Nishikawa; H. Ohoka; S. Osone; N. Sakaki; M. Sasaki; K. Shinozaki; N. Souma; M. Teshima; R. Torii; I. Tsushima; Yukio Uchihori; Tomohiko Yamamoto; Shin'ichirou Yoshida; H. Yoshii

With the Akeno Giant Air Shower Array, 581 cosmic rays above 1019 eV, 47 above 4 ) 1019 eV, and seven above 1020 eV were observed until 1998 August. The arrival direction distribution of these extremely high energy cosmic rays has been studied. While no signi—cant large-scale anisotropy is found on the celestial sphere, some interesting clusters of cosmic rays are observed. Above 4 ) 1019 eV, there are one triplet and three doublets within a separation angle of and the probability of observing 2i.5, these clusters by a chance coincidence under an isotropic distribution is smaller than 1%. The triplet is especially observed against expected 0.05 events. The distribution expected from the dark cos (h GC ) matter halo model —ts the data as well as an isotropic distribution above 2 ) 1019 and 4 ) 1019 eV, but the —t with the dark matter halo model is poorer than the isotropic distribution above 1019 eV. The arrival direction distribution of seven 1020 eV cosmic rays is consistent with that of lower energy cosmic rays and is uniform. Three of the seven are members of doublets above about 4 ) 1019 eV. Subject headings: cosmic raysgalaxies: generalGalaxy: halolarge-scale structure of universe


Astroparticle Physics | 2003

Energy determination in the Akeno Giant Air Shower Array experiment

M. Takeda; N. Sakaki; K. Honda; M. Chikawa; M. Fukushima; N. Hayashida; N. Inoue; Kenichi Kadota; F. Kakimoto; K. Kamata; S. Kawaguchi; S. Kawakami; Y. Kawasaki; N. Kawasumi; Ayman Mahrous; K. Mase; S. Mizobuchi; Y. Morizane; M. Nagano; H. Ohoka; S. Osone; Makoto Sasaki; Masaki Sasano; H.M. Shimizu; K. Shinozaki; M. Teshima; R. Torii; I. Tsushima; Yukio Uchihori; Tomohiko Yamamoto

Abstract Using data from more than 10 years of observations with the Akeno Giant Air Shower Array (AGASA), we published a result that the energy spectrum of ultra-high energy cosmic rays extends beyond the cutoff energy predicted by Greisen [Rhys. Rev. Lett. 16 (1966) 748] and Zatsepin and Kuzmin [Zh. Eksp. Teor. Fiz. 4 (1966) 114]. In this paper, we reevaluate the energy determination method used for AGASA events with respect to the lateral distribution of shower particles, their attenuation with zenith angle, shower front structure, delayed particles observed far from the core and other factors. The currently assigned energies of AGASA events have an accuracy of ±25% in event-reconstruction resolution and ±18% in systematic errors around 10 20 eV. This systematic uncertainty is independent of primary energy above 10 19 eV. Based on the energy spectrum from 10 14.5 eV to a few times 10 20 eV determined at Akeno, there are surely events above 10 20 eV and the energy spectrum extends up to a few times 10 20 eV without a GZK cutoff.


Astroparticle Physics | 1999

The anisotropy of cosmic ray arrival directions around 10 18 eV

N. Hayashida; F. Kakimoto; Yukio Uchihori; H. Ohoka; Y. Kawasaki; Y. Matsubara; N. Inoue; S. Kawaguchi; N. Sakaki; H. Yoshii; K. Shinozaki; K. Kadota; Kazuaki Murakami; K. Kamata; I. Tsushima; K. Honda; E. Kusano; N. Souma; Tomohiko Yamamoto; M. Takeda; D. Nishikawa; M. Teshima; R. Torii; M. Nagano; N. Kawasumi; H. Kitamura; Shuhei Yoshida; M. Sasaki

Abstract Anisotropy in the arrival directions of cosmic rays with energies above 1017 eV is studied using data from the Akeno 20 km2 array and the Akeno Giant Air Shower Array (AGASA), using a total of about 114 000 showers observed over 11 years. In the first harmonic analysis, we have found a strong anisotropy of ∼ 4% around 1018 eV, corresponding to a chance probability of ∼ 0.2% after taking the number of independent trials into account. with two-dimensional analysis in right ascension and declination, this anisotropy is interpreted as an excess of showers near the directions of the Galactic Center and the Cygnus region.


Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment | 1996

A Measurement of the air fluorescence yield

F. Kakimoto; Eugene C. Loh; M. Nagano; H. Okuno; M. Teshima; S. Ueno

Abstract We measured the air fluorescence yield as a function of pressure with electrons between 1.4 and 1000 MeV by means of a 90Sr β source and an electron beam. Results indicate that the fluorescence yield is proportional to electron energy loss from 1.4 to 1000 MeV. The d E d x relativistic rise in air is detected. We describe the pressure temperature dependency of air fluorescence by a formula derived from simple kinetic theory. With the aid of the 1966 US Mid-latitude Standard Atmospheric Model, we calculate the altitude dependence of fluorescence yield of an 80 MeV electron which demonstrates how this measurement could improve the longitudinal particle density profile determination of extensive air showers (EAS) observed by detectors such as the High Resolution Flys Eye and the Telescope Array.


Astroparticle Physics | 1995

The cosmic ray energy spectrum above 3 × 1018 eV measured by the Akeno Giant Air Shower Array

Shuhei Yoshida; N. Hayashida; K. Honda; M. Honda; S. Imaizumi; N. Inoue; K. Kadota; F. Kakimoto; K. Kamata; S. Kawaguchi; N. Kawasumi; Y. Matsubara; Kazuaki Murakami; M. Nagano; H. Ohoka; M. Teshima; I. Tsushima; H. Yoshii

Abstract We report the first result on the cosmic ray energy spectrum above 3 × 1018 eV measured by the Akeno Giant Air Shower Array (AGASA) from July 1990 to February 1994. The analysis method and the energy resolution of the AGASA experiment are described in some detail. The flattening of the spectrum around 1019 eV (ankle) is observed with a significance of 2.9σ. If we express the differential energy spectrum of cosmic rays of energy E (in eV) with an ankle energy Ea as J(E) = κ( E E a ) −γ m −2 s −1 sr −1 eV −1 , γ for 1018.5 eV ≤ E ≤ Ea is in good agreement with that from the previous experiment and is 3.2 ± 0.1. The slope γ above Ea depends strongly on the value Ea. For the case Ea = 1019 eV, κ = (2.3−0.2+0.1) × 10−33 and γ = 2.3−0.3+0.5 for 1019 eV ≤ E ≤ 1020 eV. If Ea = 1018.8 eV, then κ = (1.0 ± 0.1) × 10−32 and γ = 2.7−0.4+0.2 for 1018.8 eV ≤ E ≤1020 eV, after correcting for both the statistical error and the energy resolution of the present experiment. If we interpret the present results assuming an extragalactic origin for cosmic rays above 1019 eV, the observed data is consistent with either a homogeneous and isotropic distribution of sources or with localized sources at redshift of greater than ∼ 0.1. A (1.7–2.6) × 1020 eV event was observed on December 3, 1993 from the direction of l = 131° and b = −41°. This shower energy is a factor 3 larger than the second highest energy event.


The Astrophysical Journal | 1995

Very high energy gamma rays from PSR 1706-44

T. Kifune; T. Tanimori; S. Ogio; T. Tamura; Hirofumi Fujii; M. Fujimoto; T. Hara; N. Hayashida; S. Kabe; F. Kakimoto; Y. Matsubara; Yoshihiko Mizumoto; Y. Muraki; T. Suda; M. Teshima; Takashi Tsukagoshi; Yoshiyuki Watase; T. Yoshikoshi; Philip G. Edwards; John R. Patterson; M. D. Roberts; G. Rowell; Greg Thornton

We have obtained evidence of gamma-ray emission above 1 TeV from PSR1706-44, using a ground-based telescope of the atmospheric \v{C}erenkov imaging type located near Woomera, South Australia. This object, a


Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment | 1992

Akeno Giant Air Shower Array (AGASA) covering 100 km2 area

N. Chiba; K. Hashimoto; N. Hayashida; K. Honda; M. Honda; N. Inoue; F. Kakimoto; Keigo Kamata; S. Kawaguchi; Norio Kawasumi; Y. Matsubara; K. Murakami; M. Nagano; S. Ogio; H. Ohoka; To. Saito; Y. Sakuma; Itsuro Tsushima; M. Teshima; T. Umezawa; Shohei Yoshida; H. Yoshii

\gamma


The Astrophysical Journal | 1997

Very High Energy Gamma Rays from the Vela Pulsar Direction

T. Yoshikoshi; T. Kifune; S. A. Dazeley; P. G. Edwards; T. Hara; Y. Hayami; F. Kakimoto; T. Konishi; A. Masaike; Y. Matsubara; T. Matsuoka; Yoshihiko Mizumoto; Masaki Mori; H. Muraishi; Y. Muraki; T. Naito; K. Nishijima; S. Oda; S. Ogio; T. Ohsaki; John R. Patterson; M. D. Roberts; G. Rowell; T. Sako; K. Sakurazawa; R. Susukita; A. Suzuki; T. Tamura; T. Tanimori; G. J. Thornton

-ray source discovered by the COS B satellite (2CG342-02), was identified with the radio pulsar through the discovery of a 102 ms pulsed signal with the EGRET instrument of the Compton Gamma Ray Observatory. The flux of the present observation above a threshold of 1 TeV is


The Astrophysical Journal | 2003

Solar Neutron Event in Association with a Large Solar Flare on 2000 November 24

Kiyomasa Watanabe; Yasushi Muraki; Y. Matsubara; K. Murakami; T. K. Sako; H. Tsuchiya; Satoshi Masuda; M. Yoshimori; N. Ohmori; P. Miranda; N. J. Martinic; R. Ticona; A. Velarde; F. Kakimoto; S. Ogio; Y. Tsunesada; H. Tokuno; Yuji Shirasaki

\bf \sim

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S. Ogio

Osaka City University

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Kazuaki Murakami

Nagoya University of Foreign Studies

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Y. Tsunesada

Tokyo Institute of Technology

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