Extensive air showers without muon component
  Extensive air showers of cosmic rays with energies above 5.10**18 eV registered by the Yakutsk array have been analyzed. The existence of showers without muon component is found. Among them we found 5 clusters and these clusters correlate with nearest pulsars. It is found that there exist 4 classes of showers. Showers with high content of muons are mainly observed at E> 4.10**19 eV and they are formed most likely by heavy nuclei. 
A.A. Mikhailov, N.N. Efremov, E.S. Nikiforova