Phys.Rev.Lett. 81 (1998) 1163-1166 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.
Astropart.Phys. 10 (1999) 303-311 Anisotropy in the arrival directions of cosmic rays with energies above
10$^{17}$eV is studied using data from the Akeno 20 km$^2$ array and the Akeno
Giant Air ...Shower Array (AGASA), using a total of about 117,000 showers observed
during 11 years. In the first harmonic analysis, we have found strong
anisotropy of $\sim$ 4% around 10$^{18}$eV, corresponding to a chance
probability of 0.2%. 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.
With the Akeno Giant Air Shower Array (AGASA), 581 cosmic rays above 10^19eV, 47 above 4 x 10^19eV, and 7 above 10^20eV are observed until August 1998. Arrival direction distribution of these ...extremely high energy cosmic rays has been studied. While no significant large-scale anisotropy is found on the celestial sphere, some interesting clusters of cosmic rays are observed. Above 4 x 10^19eV, there are one triplet and three doublets within separation angle of 2.5^o and the probability of observing these clusters by a chance coincidence under an isotropic distribution is smaller than 1 %. Especially the triplet is observed against expected 0.05 events. The cos(\theta_GC) distribution expected from the Dark Matter Halo model fits the data as well as an isotropic distribution above 2 x 10^19eV and 4 x 10^19eV, but is a poorer fit than isotropy above 10^19eV. Arrival direction distribution of seven 10^20eV cosmic rays is consistent with that of lower energy cosmic rays and is uniform. Three of seven are members of doublets above about 4 x 10^19eV.
After our Ap.J. publication of the Akeno Giant Air Shower Array (AGASA) results in 1999 (Takeda et al., 1999), we observed nine events with energies above 4 \(\times\) 10\(^{19}\)eV until May 2000. ...This short report lists the coordinates of these events, and shows the updated energy spectrum and arrival direction map. The analysis was carried out with the same procedure employed in the Ap.J. publication.
The Telescope Array prototype detectors were installed at Akeno Observatory
and at the Utah Fly's Eye site. Using these detectors, we have observed the
Crab Nebula and AGN's since the end of 1995. ...The successful detections of TeV
gamma rays from Crab Nebula and Mkn501 are reported.
Anisotropy in the arrival directions of cosmic rays around 10^{18}eV is studied using data from the Akeno 20 km^2 array and the Akeno Giant Air Shower Array (AGASA), using a total of about 216,000 ...showers observed over 15 years above 10^{17}eV. In the first harmonic analysis, we have found significant anisotropy of \(\sim\) 4 % around 10^{18}eV, corresponding to a chance probability of \(\sim 10^{-5}\) 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. This is a clear evidence for the existence of the galactic cosmic ray up to the energy of 10^{18}eV. Primary particle which contribute this anisotropy may be proton or neutron.
Anisotropy in the arrival directions of cosmic rays with energies above 10\(^{17}\)eV is studied using data from the Akeno 20 km\(^2\) array and the Akeno Giant Air Shower Array (AGASA), using a ...total of about 117,000 showers observed during 11 years. In the first harmonic analysis, we have found strong anisotropy of \(\sim\) 4% around 10\(^{18}\)eV, corresponding to a chance probability of 0.2%. 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.
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 Telescope Array prototype detectors were installed at Akeno Observatory and at the Utah Fly's Eye site. Using these detectors, we have observed the Crab Nebula and AGN's since the end of 1995. ...The successful detections of TeV gamma rays from Crab Nebula and Mkn501 are reported.
In vivo neutron-induced radioadaptive response (RAR) was studied using zebrafish (Danio rerio) embryos. The Neutron exposure Accelerator System for Biological Effect Experiments (NASBEE) facility at ...the National Institute of Radiological Sciences (NIRS), Japan, was employed to provide 2-MeV neutrons. Neutron doses of 0.6, 1, 25, 50 and 100 mGy were chosen as priming doses. An X-ray dose of 2 Gy was chosen as the challenging dose. Zebrafish embryos were dechorionated at 4 h post fertilization (hpf), irradiated with a chosen neutron dose at 5 hpf and the X-ray dose at 10 hpf. The responses of embryos were assessed at 25 hpf through the number of apoptotic signals. None of the neutron doses studied could induce RAR. Non-induction of RAR in embryos having received 0.6- and 1-mGy neutron doses was attributed to neutron-induced hormesis, which maintained the number of damaged cells at below the threshold for RAR induction. On the other hand, non-induction of RAR in embryos having received 25-, 50- and 100-mGy neutron doses was explained by gamma-ray hormesis, which mitigated neutron-induced damages through triggering high-fidelity DNA repair and removal of aberrant cells through apoptosis. Separate experimental results were obtained to verify that high-energy photons could disable RAR. Specifically, 5- or 10-mGy X-rays disabled the RAR induced by a priming dose of 0.88 mGy of alpha particles delivered to 5-hpf zebrafish embryos against a challenging dose of 2 Gy of X-rays delivered to the embryos at 10 hpf.
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