We have studied the features of series of air shower events (AS cluster) concentrated within short intervals of time of arrival. When the number of events in the cluster reaches the maximum values in the considered data set, the arrival directions of the AS are prevailingly observed around values of right ascension α 5 h and α 20 h. These values indicate parallellism of directions between the shower directions and the galactic plane. This can be explained by the presence of Ultra-High Energy (UHE) gamma-ray sources, generating showers from their specific direction. The analysis uses three data set of 253k, 664k and 231k
events. The results are similar in the three data set
