GRAPES-3 is a mid-altitude (2200 m) and near equatorial ($11.4^{ \circ}$ North) air shower array, overlapping in its field of view for cosmic ray observations with experiments that are located in Northern and Southern hemispheres. We analyze a sample of $3.7\times10^9$ cosmic ray events collected by the GRAPES-3 experiment between 1 January 2013 and 31 December 2016 with a median energy of $\sim16$ TeV for study of small-scale ($<60^{ \circ}$) angular scale anisotropies. We observed two structures labeled as A and B, deviate from the expected isotropic distribution of cosmic rays in a statistically significant manner. Structure `A' spans $50^{ \circ}$ to $80^{ \circ}$ in the right ascension and $-15^{ \circ}$ to $30^{ \circ}$ in the declination coordinate. The relative excess observed in the structure A is at the level of $(6.5\pm1.3)\times10^{ -4}$ with a statistical significance of 6.8 standard deviations. Structure `B' is observed in the right ascension range of $110^{ \circ}$ to $140^{ \circ}$. The relative excess observed in this region is at the level of $(4.9\pm1.4)\times10^{ -4}$ with a statistical significance of 4.7 standard deviations. These structures are consistent with those reported by Milagro, ARGO-YBJ, and HAWC. These observations could provide a better understanding of the cosmic ray sources, propagation and the magnetic structures in our Galaxy.
Categories: astro-ph.HE