N. Hayashida

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

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

The anisotropy of cosmic ray arrival directions around 10 18 eV

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.

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

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.

Energy spectrum of primary cosmic rays above 1017.0 eV determined from extensive air shower experiments at Akeno

The energy spectrum of primary cosmic rays above 1017.0 eV has been updated from data collected with two extensive air shower arrays operating at Akeno, one with area 1 km2 and the other with area 20 km2. Along with the authors previous results in the lower energy region, the energy spectrum has been determined over about five decades of energy from 1014.5 eV to 1019.8 eV. A change in the index of the power-law energy spectrum is observed around 1017.8 eV, as well as the usual features, namely the knee around 1015.7 eV and the ankle around 1019.0 eV. The indices of the differential power-law energy spectrum are: (2.62+or-0.12) below 1015.7 eV, (3.02+or-0.03) for 1015.7 approximately 1017.8 eV and (3.16+or-0.08) for 1017.8 approximately 1018.8 eV. There is an indication of a flattening of the spectrum above approximately 1018.8 eV with an index of (2.8+or-0.3). The flux above 1018 eV is (1.5 approximately 2.4)*10-12 m-2s-1sr-1 and is in good agreement with other experiments. The number of showers above 1019.5 eV is seven for an exposure of 80 km2 yr sr and further investigation by a new Akeno giant air shower array (AGASA), whose operation has started, is necessary to determine a cutoff energy in the spectrum, if any.

Energy Spectrum of Primary Cosmic Rays Between 10**14.5-ev and 10**18-ev

Size spectra of electrons (Ne) and muons (Nmu ) are obtained from the Akeno extensive air-shower experiment. The primary spectrum estimated from each spectrum is the same and is expressed by J(E0)dE0(4.0-5.0)*10-23(E0/1015.67)- gamma dE0 m-2 s-1 sr-1 where gamma =2.62+or-0.12 below and gamma =3.02+or-0.05 above 1015.67 eV. There is no other significant change of slope in either the electron or the muon size spectrum beyond the corresponding energy 1015.67 eV.

Very high energy gamma rays from PSR 1706-44

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

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

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Observations of TeV Gamma-Ray Flares from Markarian 501with the Telescope Array Prototype

-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

OBSERVATION OF THE 7 TEV GAMMA RAYS FROM THE CRAB USING THE LARGE ZENITH ANGLE AIR CERENKOV IMAGING TECHNIQUE

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Telescope array for advanced studies of cosmic rays at the highest and TEV energies

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