Statistics of clustering of ultrahigh energy cosmic rays and the number oftheir sources

Observation of clustering of ultrahigh energy cosmic rays (UHECR) suggests that they are emitted by compact sources. Assuming small (<3 degrees) defle ction of UHECR during the propagation, the statistical analysis of clusteri ng allows an estimate of the spatial density of the sources h(*), including those not yet observed. When applied to astrophysical models involving ext ragalactic sources, the estimate based on 14 events with energy E > 10(20) eV gives h(*) similar to 6 x 10(-3) Mpc(-3). With increasing statistics, th is estimate may lead to exclusion of some models.