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H. Matsumoto 1 , A . Iyono 1 , I. Yamamoto 1 ,

The primary energy spectrum measured by using the time structure of extensive air showers with compact EAS arrays (ID441). H. Matsumoto 1 , A . Iyono 1 , I. Yamamoto 1 , K . Okei 2 , S.Tsuji 2 , T. Nakatsuka 3 , N. Ochi 4 , S . Ohara 5 , T. Konishi 5 , N. Takahashi 6

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H. Matsumoto 1 , A . Iyono 1 , I. Yamamoto 1 ,

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  1. The primary energy spectrum measured by using the time structure of extensive air showers with compact EAS arrays(ID441) H. Matsumoto1, A. Iyono1, I. Yamamoto1, K. Okei2, S.Tsuji2, T. Nakatsuka3, N. Ochi4, S. Ohara5, T. Konishi5, N. Takahashi6 and the LAAS experiments 1Okayama University of Science, Okayama 700-0005, Japan 2Kawasaki Medical School, Kurashiki 701-0192, Japan 3Okayama Shoka University, Okayama 700-8601, Japan 4 Toyo University, Bunkyoku, Tokyo 112-8606, Japan 5Nara Sangyo University, Nara 636-8503, Japan 6Hirosaki University, Hirosaki 036-8560, Japan ECRS2012, July 3-7, 2012, Moscow, Russia

  2. Linsley’s method • Extensive air shower (EAS) thickness depends on the core distance r, the zenith angle θ and the primary energy E0. • EAS thickness is defined by using the dispersion σt of arrival time distribution of EAS particles. • The dispersion <σt> of arrival time distribution of EAS particles as a function of EAS core distance r.

  3. Aims of this applications • The estimate of the primary energy spectrum by using Linsley’s EAS time structure method with compact EAS arrays. • Primary energy region : 10PeV – ~10EeV • Single observation (OUS1 array) • Coincidence observation (OUS1 array and OUS4 array) • Observation for the primary cosmic ray by using multi EAS arrays spread over in Japan. (LAAS experiment) • Investigation the Gerasimova-Zatsepin events • Anisotropy

  4. OUS1&4 array • Detector • Plastic scintillation counter (50cm×50cm×5cm, PMT:HAMAMATSU H7195) • Data acquisition system • ADC (Lecroy 2249W) • TDC (Kaizuworks 3781) • GPS module (Kaizuworks 3051A) • Shift register • (MPK NIM-ANY) • Trigger condition • More than 3 detectors • (within 2.5μs time window) • Array size • ~200m2

  5. OUS4 detectors • Detector • Plastic scintillation counter • Top&bottom: • (40cm×50cm×1cm, PMT:HAMAMATSU H7195) • Side: • (50cm×50cm×5cm, PMT:HAMAMATSU H7195) • Data acquisition system • ADC (Lecroy 2249W) • TDC (Kaizuworks 3781) • GPS module • Shift register • Trigger condition • Top&bottom • (within 2.5μs time window) • Restriction angle • 25.6 [deg.] Linsley’ method can be applied in case of rather large core distance, but arrival direction can not be determined Zenith angle restriction are needed. This was pointed out at ISVHECR2006 in Weihai

  6. Estimation procedure of primary energy OUS1 array • Arrival time distribution : ti (i=1,2,…,n) • Gamma distribution • Estimation of the dispersion σt • estimator : median • σt → r • Lateral distribution function • (r, n)→E0 data: (ti, n)

  7. Detector simulation: energy distribution FWHM:101.73 (1017.16-1018.89) 100.50 (1018.18-1018.68) • AIRES • QGSJETII-3 • / Hillas Splitting Algorithm • Proton • Single power-law spectrum @3.2EeV • Restriction of the zenith angle θ • OUS1 θ<60 [deg.] • OUS1+4 θ<25.6 [deg.] @0.32EeV FWHM: 101.58 (1016.39-1017.97) 100.66 (1017.07-1017.73)

  8. Systematics of energy resolutions @0.32EeV OUS1: 195% OUS1+4: 69% @3.2EeV OUS1: 145% OUS1+4: 51%

  9. Acceptance OUS1 ~1/50 OUS1+4

  10. Conversion of spectral indices Conversion table from observed spectral index |a’| to primary spectral index |a|.

  11. Data analysis • Data period: (one more year data period added after ICRC2011) • OUS1 2006/4 – 2011/12 • OUS1+4 2008/8 – 2011/12 • Restriction of the zenith angle θ • OUS1 θ<60 [deg.] • OUS1+4 θ<25.6 [deg.] Noise rate ~0.4%

  12. Time difference between OUS1 and OUS4 Coincident events (within 10μsec. ) GPS time accuracy : 1μsec.

  13. Observed flux at OUS1 array

  14. Results: Primary energy spectrum (OUS1) Single power-law spectrum

  15. Observed flux at OUS1+4 array

  16. Results: Primary energy spectrum (OUS1+4) Single power-law spectrum

  17. Derived by the application of Linsley’s EAS time structure method to LAAS-OUS1single array observations.

  18. Comparison of E・Flux [m-2s-1sr-1] Compiled by Tsunesada-san at UHCR2012

  19. Conclusions • The primary energy spectrum is determined by compact EAS arrays according to the Linsley’s EAS structure method. • The primary energy resolution of OUS1 have been improved by restricting the EAS zenith angle by using OUS4. But its acceptance decreased ~1/50. • The obtainedspectral index values: • OUS1: -2.51 (+0.23 -0.27) (1016-1019.5eV)-3.20 (+0.53 -0.97) (1016-1018.5eV)-2.09 (+0.10 -0.11)(1018-1019.5eV) • OUS1+4: -3.13 (+0.33 -0.39)(1016-1019.5eV)-3.60 (+0.42 -0.51)(1016-1018.5eV) • The primary energy spectrum of the OUS1+4 is steeper than that of the OUS1 due to minimizing systematic errors. • Observed EJ spectra is consistent with other experiments.

  20. EJ, E3J

  21. Observed flux at OUS1 and OUS1+4

  22. UHCR2012 compiled by Tsunesada-san g1 g2 g3 Log10(EA) Log10(Es) AGASA 3.16(0.08) 2.78(0.3) - 19.01 Yakutsk 3.29(0.17) 2.74(0.20) - 19.01(0.01) - HiRes 3.25(0.01) 2.81(0.03) 5.1(0.7) 18.65(0.05) 19.75(0.04) Auger 3.27(0.02) 2.68(0.01) 4.2(0.1) 18.61(0.01) 19.41(0.02) TA 3.33(0.04) 2.68(0.04) 4.2(0.7) 18.69(0.03) 19.68(0.09)

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