A doublet of cosmic-ray events with primary energies $>10^{20}$ eV

The Telescope Array Collaboration has observed a cosmic-ray event with estimated primary energy of $1.38 \cdot 10^{20}$ eV whose arrival direction coincides [T. Abu-Zayyad et al. (Telescope Array Collaboration), arXiv:1205.5984], given the angular resolution of $1.5^{\circ}$, with that of an event with estimated primary energy of $1.23 \cdot 10^{20}$ eV observed by the Pierre Auger Observatory. The total number of events with energies $>10^{20}$ eV published by both experiments is six. I estimate the statistical significance of the doublet, which is rather weak, and point out that the arrival directions of events in the doublet coincide with the Galactic $X$-ray source Aql X-1.