학술논문
Small-scale cosmic ray anisotropy observed by the GRAPES-3 experiment at TeV energies
Document Type
Working Paper
Author
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.; Nayak, P. K.; Nonaka, T.; Nakamura, 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.
Source
Subject
Language
Abstract
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.