Why do Auger and Telescope Array spectra differ above $3 \times 10^{19}\,\mathrm{eV}$?

After cross-calibration of energy scales, the Telescope Array flux above $\sim 3 \times 10^{19}\ \mathrm{eV}$ and its suppression energy remain higher than those of the Pierre Auger Observatory. Determine whether the residual difference is instrumental (energy-scale nonlinearity, aperture, atmospheric corrections) or a real dependence on sky direction that would imply a nearby source in the northern sky. Answer: yes or no for a direction-dependent flux, with significance after systematics, evaluated in the declination band seen by both.

Measurements in the common declination band with identical detector types at both sites, such as Auger-type surface stations operated at the Telescope Array site.