Search for non-random feature in arrival times of air showers

We have searched for non-random components in arrival times of air showers of mean energy of 1 PeV. By counting the number of air showers observed within time windows of 20-60 minutes, we find small deviation of air shower data from the conventional view of uniformly random cosmic ray injection. The arrival directions of the non-random events concentrate at the direction of the Galactic plane. Though the significance of these events is not so high because of the lack of statistics, they may be induced by sporadic non-random injection of ultra-high energy γ-rays from the Galactic plane