Linsley's EAS time structure method for the primary cosmic ray spectrum at LAAS
01 Sep 2011
1Dept. of Fundamental Science, Okayama University of Science, Okayama 700-0005, Japan
2Kawasaki Medical School, Kurashiki 701-0192, Japan
3Nara University of Industry, Nara 636-8503, Japan
4Yonago National College of Technology, Tottori 683-8502, Japan
5Kinki University, Osaka 577-8502, Japan
6Dept. of Physics, Hirosaki University, Hirosaki 036-8561, Japan
7Dept. of Information and Computer Engineering, Okayama University of Science, Okayama 700-0005, Japan
8Okayama Shoka University, Okayama 700-86011, Japan
9Kochi University, Kochi 780-8520, Japan
10Ashikaga Institute of Technology, Ashikaga 326-8558, Japan
Abstract. We have installed a shift register system of extensive air show (EAS) particles in a compact EAS array built on the rooftop of the Faculty of Engineering building in the campus of Okayama University of Science and being operated since April 2006 as part of Large Area Air Shower (LAAS) experiments , in order to register each arrival time of EAS particles within 5 μs. Detector simulations based on the database obtained from one of the standard cosmic ray propagation simulator in the atmosphere (AIRES) have also been carried out and the procedures to estimate the primary cosmic ray energy from the Linsley's method have been developed and examined. Applying Linsley's method to the EAS data obtained by our EAS arrays and the simulation results, we derived the energy spectrum from 1016 eV to 1019.5 eV. Consequently, we obtained the power-law index of −3.2 (+0.46−0.8) in the primary energy range of 1016 eV to 1018.5 eV, and obtained that a change around 1018 eV appeared if not taking account of the zenith angle distribution of primary cosmic rays. We compared the obtained energy spectrum with other experimental data above 1016 eV energies, and showed the two components of power-law energy spectra well described our data. We also showed the improvement of energy resolution by applying the restriction of zenith angle of primary cosmic rays in our simulation results, as well as the potential of the Linsley's method with a compact EAS array.
Citation: Iyono, A., Matsumoto, H., Okei, K., Tsuji, S., Ohara, S., Ochi, N., Konishi, T., Takahashi, N., Yamamoto, I., Nakatsuka, T., Nakamura, T., Ohmori, N., and Saito, K.: Linsley's EAS time structure method for the primary cosmic ray spectrum at LAAS, Astrophys. Space Sci. Trans., 7, 335-344, doi:10.5194/astra-7-335-2011, 2011.