A2: Do the AGASA clusters imply that Auger will identify many discrete sources, each with enough showers to study their spectra and compositions separately? What might we learn from magnetic spectroscopy?

The AGASA clusters are an intriguing and exciting result. They are so important (and perhaps surprising in some respects) that a high level of statistical confidence is required before asserting that they are definitely there for study by Auger.

The first publication of the cluster existence by AGASA was when that experiment had detected 38 events with energies above 40 EeV. The Auger Observatory (with 6000 km^2 of surface array) would expect to collect approximately 440 showers per year with energies above 40 EeV. After 5 years, the total should be nearly 60 times the 38 AGASA showers. For any souce giving 2 showers as the expected number for AGASA, Auger would expect to record 120 showers. The AGASA triplets might suggest even higher numbers of on-source showers. Judging by the AGASA clusters, all of these showers should arrive from almost the same celestial direction.

Clearly, Auger could identify sources at much lower cosmicr ray flux levels. With 2200 showers over the full sky (5 years times 440 per year), a target window of 2 degrees radius would have an expected number of less than 1 shower. A positive detection might be claimed by a cluster of 6 directions within the target solid angle. Comparing this with an estimated 120 showers for the AGASA sources, Auger would be sensitive to sources that are 20 times weaker. So, Yes, the AGASA clusters imply that Auger should expect to identify a large number of discrete sources over the whole sky.

Some of the sources might have showers numbering more than 120 after 5 years. The background (less than 1 shower) is negligible. So the source spectrum could be measured. It should also be possible to tell if there are heavy nuclei or pure protons.