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arXiv · 1911.04715

The angular resolution of GRAPES-3 EAS array after correction for the shower front curvature

V. B. Jhansi·S. Ahmad·M. Chakraborty·S. R. Dugad·S. K. Gupta·B. Hariharan·Y. Hayashi·P. Jagadeesan·A. Jain·P. Jain·S. Kawakami·H. Kojima·S. Mahapatra·P. K. Mohanty·S. D. Morris·P. K. Nayak·A. Oshima·D. Pattanaik·P. S. Rakshe·K. Ramesh·B. S. Rao·L. V. Reddy·S. Shibata·F. Varsi·M. Zuberi
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Abstract

The angular resolution of an extensive air shower (EAS) array plays a critical role in determining its sensitivity for the detection of point $\gamma$-ray sources in the multi-TeV energy range. The GRAPES-3 an EAS array located at Ooty in India (11.4$^{\circ}$N, 76.7$^{\circ}$E, 2200 m altitude) is designed to study $\gamma$-rays in the TeV-PeV energy range. It comprises of a dense array of 400 plastic scintillators deployed over an area of 25000 m$^2$ and a large area (560 m$^2$) muon telescope. A new statistical method allowed real time determination of the propagation delay of each detector in the GRAPES-3 array. The shape of shower front is known to be curved and here the details of a new method developed for accurate measurement of the shower front curvature is presented. These two developments have led to a sizable improvement in the angular resolution of GRAPES-3 array. It is shown that the curvature depends on the size and age of an EAS. By employing two different techniques, namely, the odd-even and the left-right methods, independent estimates of the angular resolution are obtained. The odd-even method estimates the best achievable resolution of the array. For obtaining the angular resolution, the left-right method is used after implementing the size and age dependent curvature corrections. A comparison of the angular resolution as a function of EAS energy by these two methods shows them be virtually indistinguishable. The angular resolution of GRAPES-3 array is 47$^{\prime}$ for energies E$>$5 TeV and improves to 17$^{\prime}$ at E$>$100 TeV and finally approaching 10$^{\prime}$ at E$>$500 TeV.

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V. B. Jhansi, S. Ahmad, M. Chakraborty, S. R. Dugad, S. K. Gupta, B. Hariharan, Y. Hayashi, P. Jagadeesan, A. Jain, P. Jain, S. Kawakami, H. Kojima, S. Mahapatra, P. K. Mohanty, S. D. Morris, P. K. Nayak, A. Oshima, D. Pattanaik, P. S. Rakshe, K. Ramesh, B. S. Rao, L. V. Reddy, S. Shibata, F. Varsi, M. Zuberi. 2019-11-12. The angular resolution of GRAPES-3 EAS array after correction for the shower front curvature. https://doi.org/10.1088/1475-7516%2F2020%2F07%2F024

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