Search for TeV γ Rays from the Direction of Extremely High-Energy Cosmic-Ray Events

川田 和正


   The detection of 8 extremely high-energy (EHE) cosmic rays with energies above 1020eV in recent ten years gives question about their origin and the acceleration mechanism if it is. It is dramatically confirmed that the cosmic-ray spectrum does not end with well known GZK cutoff. But, it is undeniable fact that there is not seen any decisive optical counterpart, neither Galactic nor extragalactic exotic object, at the arrival directions of EHE cosmic rays exceeding 1020eV. Such an EHE cosmic ray, even as a charged particle, keeps almost straight trajectory in the Galactic magnetic field. And, EHE particles, even though gamma rays or protons, can not arrive from the space beyond 60 Mpc (200 million light years) through the collision with cosmic microwave background photons. This work is exploratory analysis whether TeV gamma rays come significantly or not from the arrival directions of these EHE cosmic rays, expecting to find a clue to solve this mystery. We analyzed directions of 8 EHE cosmic-ray events observed by AGASA and Fly's Eye experiments. No clearly significant excess is seen in directions of these EHE cosmicrays. An upper limit was given for the flux of TeV gamma rays from 3C147 lying near the highest energy (3×1020 eV) the Fly's Eye event as 8.0×10-13cm-2s-1.