Abstract. This paper summarizes measurement results of the UHECR energy spectrum and arrival directions. Various scenarios trying to explain the flat AGASA spectrum (no GZK cutoff) are recalled. Recent HiRes data are, however, consistent with the expected GZK cutoff, so that for E > 10²⁰ eV the fluxes measured by the two experiments diverge by more than one order of magnitude. The multiple events, observed by AGASA, seem not to be statistical fluctuations and we analyse the information contained in them. The Pierre Auger Observatory (in construction) is expected to dispel the doubts about existence of the GZK cutoff as well as those about the nature of the multiplets.

Print publication: Issue 5 (May 2003)
Received 20 November 2002, in final form 12 December 2002
Published 9 April 2003