Indications of Intermediate-Scale Anisotropy of Cosmic Rays with Energy Greater Than 57 EeV in the Northern Sky Measured with the Surface Detector of the Telescope Array Experiment

We have searched for intermediate-scale anisotropy in the arrival directions of ultrahigh-energy cosmic rays with energies above 57~EeV in the northern sky using data collected over a 5 year period by the surface detector of the Telescope Array experiment. We report on a cluster of events that we call the hotspot, found by oversampling using 20$^circ$-radius circles. The hotspot has a Li-Ma statistical significance of 5.1$sigma$, and is centered at R.A.=146.7$^{circ}$, Dec.=43.2$^{circ}$. The position of the hotspot is about 19$^{circ}$ off of the supergalactic plane. The probability of a cluster of events of 5.1$sigma$ significance, appearing by chance in an isotropic cosmic-ray sky, is estimated to be 3.7$times$10$^{-4}$ (3.4$sigma$).