Observation of a Beam of Ultrarelativistic Particles and the Cherenkov Resonance

Previously we have reported the detection of a sequence of three particle arrival events at energies above 10 19 eV during one day and from a small sky region by two extensive air shower (EAS) arrays. We have shown that the probability of a chance coincidence of the three events is very low and suggested the arrival of a short-lived particle beam at the Earth. Here we refine the energies of the recorded particles and discuss a possible beam formation mechanism that explains the observational results.