When the Pierre Auger Project was proposed in 1998 the stated scientific objective was "to discover and understand the source or sources of cosmic rays with energies exceeding 10**19 eV." A unique partnership of 17 countries has come together to pursue this science. The Pierre Auger Observatory (PAO), completed in June 2008, has accumulated data since January of 2004, and has already yielded results that are the first crucial steps toward those scientific goals.
The growing Auger data set will address vital questions in astrophysics and particle physics. The PAO will continue to map the southern sky to strengthen the correlation of the highest energy events with extragalactic sources. A continuously enriched sample of hybrid events with measured longitudinal development will improve our understanding of the cosmic ray composition and features of particle interactions from LHC energies to those well beyond. Resolving the puzzle of apparent excess of muons will benefit from increasing statistics. A precise spectrum measurement in the ankle region with the help of the AMIGA in-fill and the HEAT high elevation telescopes will help determine the transition from galactic to extragalactic sources. Based on hints in the data the search for galactic sources of neutrons and photons may well be fruitful. Finally a search for EeV neutrinos will continue to be of great interest.
This award will provide partial funding for the continuing operation of the PAO in Argentina. Collaborating countries fund the operations of the Observatory in proportion to the number of senior authors they have on Auger science publications. The US portion of these operating costs is being shared equally by the National Science Foundation and the US Department of Energy.
The study of the highest energy cosmic rays, the most energetic particles in nature, will have broader impacts on the understanding of particle physics at the highest energies as well as astrophysics. The PAO has been a highly successful venue for the training of students and postdocs. The centerpiece of outreach to Malargüe, Argentina, and other nearby communities, the Auger Visitor Center attracts increasing numbers of visitors, typically 6000 each year with the total now exceeding 45,000 since 2001. The Auger collaboration has sponsored two science fairs and has given numerous lectures in the local communities and schools. The daily public release of about 1% of reconstructed events is being used for school projects in many locations.
