By August 1998, AGASA had observed 47 events above 4x10^19 eV and
7 above 10^20 eV.
No significant large-scale anisotropy was observed.
However there were 3 doublet and 1 triplet clusters (within 2.5 deg separation).
Probablility of these clusters arising randomly is less than 1%.
These data suggest point sources, but retracing the trajectories through the
galactic and intergalactic magnetic fields complicates their identification.
Possibilities include:
stellar sources in nearby galaxies
galactic objects such as the Cygnus Loop (NGC 6992/95), Cyg X-3, and PSR 2053+36
extragalactic objects such as the interacting galaxy Mrk 359
new physics: quark novae, z-boson decays, monopoles, violation of Lorentz invariance
and more...
