Clusters of EAS with electron number >~ 10^4
  We perform cluster analysis of arrival times of extensive air showers (EAS) registered with the EAS-1000 Prototype array in the period from August, 1997 till February, 1999. We present twenty cluster events each consisting of one or several EAS clusters, study the dynamics of their development, and analyze the angular distribution of EAS in clusters. We find that there may be certain correlation between EAS clusters with mean electron number $\sim10^5$ on the one hand and gamma-ray bursts and ultrahigh energy cosmic rays on the other. 
Yu. A. Fomin, G. V. Kulikov, M. Yu. Zotov