The Fortuitous Latitude of the Pierre Auger Observatory and Telescope Array for Reconstructing the Quadrupole Moment

Understand

Determining anisotropies in the arrival directions of cosmic rays at the highest energy is an important task in astrophysics.

• It is common and useful to partition the sky into spherical harmonics as a measure of anisotropy.
• The two lowest nontrivial spherical harmonics, the dipole and the quadrupole, are of particular interest, since these distributions encapsulate a dominant single source and a plane of sources, as well as offering relatively high statistics.
• The best experiments for the detection of ultra high energy cosmic rays currently are all ground-based, with highly nonuniform exposures on the sky resulting from the fixed experimental locations on the earth.