M. Teshima

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

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.

Energy determination in the Akeno Giant Air Shower Array experiment

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.

A Measurement of the air fluorescence yield

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.

Cluster analysis of extremely high-energy cosmic rays in the northern sky

Abstract The arrival directions of extremely high energy cosmic rays (EHECR) above 4×10 19 eV, observed by four surface array experiments in the northern hemisphere, are examined for coincidences from similar directions in the sky. The total number of cosmic rays is 92. A significant number of double coincidences (doublet) and triple coincidences (triplet) is observed on the supergalactic plane within the experimental angular resolution. The chance probability of such multiplets from a uniform distribution is less than 1% if we consider a restricted region within ±10° of the supergalactic plane. Though there is still a possibility of chance coincidence, the present results on small angle clustering along the supergalactic plane may be important in interpreting EHECR enigma. An independent set of data is required to check our claims.The arrival directions of extremely high energy cosmic rays (EHECR) above

Development of atmospheric monitoring system at Akeno observatory for the Telescope Array project

4times10^{19}

The arrival direction distribution of Extremely High En- ergy cosmic rays observed by AGASA

eV, observed by four surface array experiments in the northern hemisphere,are examined for coincidences from similar directions in the sky. The total number of cosmic rays is 92.A significant number of double coincidences (doublet) and triple coincidences (triplet) are observed on the supergalactic plane within the experimental angular resolution. The chance probability of such multiplets from a uniform distribution is less than 1 % if we consider a restricted region within

Energy estimation of AGASA events

pm 10^{circ}

Telescope Array Project

of the supergalactic plane. Though there is still a possibility of chance coincidence, the present results on small angle clustering along the supergalactic plane may be important in interpreting EHECR enigma. An independent set of data is required to check our claims.

Chemical Composition of Ultra-high Energy Cosmic Rays Observed by AGASA

We have developed an atmospheric monitoring system for the Telescope Array experiment at Akeno Observatory. It consists of a Nd:YAG laser with an alt-azimuth shooting system and a small light receiver. This system is installed inside an air conditioned weather-proof dome. All parts, including the dome, laser, shooter, receiver, and optical devices are fully controlled by a personal computer utilizing the Linux operating system. It is now operated as a back-scattering LIDAR system. For the Telescope Array experiment, to estimate energy reliably and to obtain the correct shower development profile, the light transmittance in the atmosphere needs to be calibrated with high accuracy. Based on observational results using this monitoring system, we consider this LIDAR to be a very powerful technique for Telescope Array experiments. The details of this system and its atmospheric monitoring technique will be discussed.