Statistics of clustering of ultrahigh energy cosmic rays and the number of their sources.

Observation of clustering of ultrahigh energy cosmic rays (UHECR) suggests that they are emitted by compact sources. Assuming small ( <3 degrees ) deflection of UHECR during the propagation, the statistical analysis of clustering allows an estimate of the spatial density of the sources h(*), including those not yet observed. When applied to astrophysical models involving extragalactic sources, the estimate based on 14 events with energy E>10(20) eV gives h(*) approximately 6x10(-3) Mpc(-3). With increasing statistics, this estimate may lead to exclusion of some models.