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  • Small-scale Cosmic-Ray Anis...
    Chakraborty, M.; Ahmad, S.; Chandra, A.; Dugad, S. R.; Goswami, U. D.; Gupta, S. K.; Hariharan, B.; Hayashi, Y.; Jagadeesan, P.; Jain, A.; Jain, P.; Kawakami, S.; Koi, T.; Kojima, H.; Mahapatra, S.; Mohanty, P. K.; Moharana, R.; Muraki, Y.; Nakamura, T.; Nayak, P. K.; Nonaka, T.; Oshima, A.; Pant, B. P.; Pattanaik, D.; Paul, S.; Pradhan, G. S.; Rameez, M.; Ramesh, K.; Saha, S.; Sahoo, R.; Scaria, R.; Shibata, S.; Tabata, T.; Takamaru, H.; Tanaka, K.; Varsi, F.; Yamazaki, K.; Zuberi, M.

    The Astrophysical journal, 01/2024, Letnik: 961, Številka: 1
    Journal Article

    Abstract GRAPES-3 is a mid-altitude (2200 m) and near-equatorial (11.°4N) air shower array, overlapping in its field of view for cosmic-ray observations with experiments that are located in the Northern and Southern Hemispheres. We analyze a sample of 3.7 × 10 9 cosmic-ray events collected by the GRAPES-3 experiment between 2013 January 1 and 2016 December 31 with a median energy of ∼16 TeV for study of small-scale (<60°) angular-scale anisotropies. We observed two structures, labeled A and B, that deviate from the expected isotropic distribution of cosmic rays in a statistically significant manner. Structure A spans 50°–80° in R.A. and from −15° to 30° in decl. The relative excess observed in structure A is at the level of (6.5 ± 1.3) × 10 −4 with a statistical significance of 6.8 standard deviations. Structure B is observed in the R.A. range 110°–140° and at decl. from −10° to 30°. The relative excess observed in this region is at the level of (4.9 ± 1.4) × 10 −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 sources of cosmic rays, their propagation, and the magnetic structures in our Galaxy.