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C. T. Yan

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C. T. Yan

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  1. ** ** Multi-TeV Observation on the Galactic Cosmic Ray Anisotropy in the Tail-In and Cygnus Regions by the Tibet-III Air Shower Array C. T. Yan For the Tibet AS Collaboration Inst. for Cosmic Ray Research, Univ. of Tokyo 08 / 12 / 2006 ” Locating PeV Cosmic-Ray Accelerators: Future Detectors in Multi-TeV Gamma-Ray Astronomy ” 6 – 8 December, 2006 - Adelaide, Australia

  2. The Tibet AS Collaboration M.Amenomori,1 S.Ayabe,2 X.J.Bi,3 D.Chen,4 S.W.Cui,5 Danzengluobu,6 L.K.Ding,3 X.H.Ding, 6 C.F.Feng,7 Zhaoyang Feng,3 Z.Y.Feng,8 X.Y.Gao,9 Q.X.Geng,9 H.W.Guo,6 H.H.He,3 M.He,7 K.Hibino,10 N.Hotta,11 HaibingHu,6 H.B.Hu,3 J.Huang,12 Q.Huang,8 H.Y.Jia,8 F.Kajino,13 K.Kasahara,14Y.Katayose,4 C.Kato,15 K.Kawata,12 Labaciren,6 G.M.Le,16 A.F. Li,7 J.Y.Li,7 Y.-Q. Lou,17 H.Lu,3 S.L.Lu,3 X.R.Meng,6 K.Mizutani,2,18 J.Mu,9 K.Munakata,15 A.Nagai,19 H.Nanjo,1 M.Nishizawa,20 M.Ohnishi,12 I.Ohta,21 H.Onuma,2 T.Ouchi,10 S.Ozawa,12 J.R.Ren,3 T.Saito,22 T.Y.Saito,23 M.Sakata,13 T.K.Sako,12 T.Sasaki,10 M.Shibata,4 A.Shiomi,12 T.Shirai,10 H.Sugimoto,24 M.Takita,12 Y.H.Tan,3 N.Tateyama,10 S.Torii,18 H.Tsuchiya,25 S.Udo,12 B. Wang,9 H.Wang,3 X.Wang,12 Y.G.Wang,7 H.R.Wu,3 L.Xue,7 Y.Yamamoto,13 C.T.Yan,12 X.C.Yang,9 S.Yasue,26 Z.H.Ye,16 G.C.Yu,8 A.F.Yuan,6 T.Yuda,10 H.M.Zhang,3 J.L.Zhang,3 N.J.Zhang,7 X.Y.Zhang,7 Y.Zhang,3 Yi Zhang,3 Zhaxisangzhu,6 and X.X.Zhou 8 (1) Dep. of Phys., Hirosaki Univ., Hirosaki, Japan (2) Dep. of Phys., Saitama Univ., Saitama, Japan (3) Key Lab. of Particle Astrophys., IHEP, CAS, Beijing, China (4) Fac. of Eng., Yokohama National Univ., Yokohama , Japan (5) Dep. of Phys., Hebei Normal Univ., Shijiazhuang, China (6) Dep. of Math. and Phys., Tibet Univ., Lhasa, China (7) Dep. of Phys., Shandong Univ., Jinan, China (8) Inst. of Modern Phys., South West Jiaotong Univ., Chengdu, China (9) Dep. of Phys., Yunnan Univ., Kunming, China (10) Fac. of Eng., Kanagawa Univ, Yokohama, Japan (11) Fac. f of Educ., Utsunomiya Univ., Utsunomiya, Japan (12) ICRR., Univ. of Tokyo, Kashiwa, Japan (13) Dep of Phys., Konan Univ., Kobe, Japan (14) Fac. of Systems Eng., Shibaura Inst. of Tech., Saitama, Japan (15) Dep. of Phys., Shinshu Univ., Matsumoto, Japan (16) Center of Space Sci. and Application Research, CAS, Beijing, China (17) Phys. Dep. and Tsinghua Center for Astrophys., Tsinghua Univ., Beijing, China (18) Advanced Research Inst. for Sci. and Engin., Waseda Univ., Tokyo, Japan (19) Advanced Media Network Center, Utsunomiya University, Utsunomiya, Japan (20) National Inst. of Info., Tokyo, Japan (21) Tochigi Study Center, Univ. of the Air, Utsunomiya, Japan (22) Tokyo Metropolitan College of Industrial Tech., Tokyo, Japan (23) Max-Planck-Institut fuer Physik, Muenchen, Germany (24) Shonan Inst. of Tech., Fujisawa, Japan (25) RIKEN, Wako, Japan (26) School of General Educ.,Shinshu Univ., Matsumoto, Japan

  3. Outline • The Tibet air-shower array • Anisotropy of galactic cosmic rays (*) • The tail-in and loss-cone model • Gamma/hadron separation method • Discrimination of gamma/hadron in the array • Gamma/Hadrons judgment by comparisons (**) • Back-check by the Crab Nebula • Investigation on two anisotropy components • The ‘tail-in’ anisotropy component • Excesses from the Cygnus region(***) • Conclusive remarks

  4. The Tibet air shower array View around the Tibet III array (90.52E, 30.10N;4300m a.s.l.) in 2003 • Located at an elevation of 4300 m (Yangbajing in Tibet, China) • Atmospheric depth 606 g / cm2 • Wide field of view ( ~ 2 sr field of view) • High duty cycle ( > 90%) • Modal energy: ~ 3 TeV • Angular resolution: ~ 0.9o • Data sample used (1997 ~ 2005, 37 * 109) Large-scale observation

  5. Anisotropy of galactic cosmic rays 4.0 TeV 6.2 TeV 12 TeV 50 TeV 300 TeV i) Temporal variation ii) Anisotropy towards the Cygnus region iii) Energy dependency iv) Anisotropy fade away ~ 300 TeV From Science, V314, pp.439 – 443 (2006), by the analysis method (I)

  6. loss-cone tail-in Galactic plane Tail-in and loss-cone model of the anisotropy Ref:K. Nagashima, K. Fujimoto, R.M. Jacklyn, J. Geophys. Res. V103, 17429 (1998). < 1 TeV • Heliospheric magnetic field is not enough for TeV CR anisotropy. • TeV CR anisotropy should be caused by the Local Interstellar Could (~ a few pc). RL~ 0.01pc (for 10TeV proton in 1mG)

  7. Gamma-initiated air shower Concentrated Smooth Uniformity … Hadron-initiated air shower Scattered Large fluctuation Sub core structure … Simulations: Corsika-6.204 for air showers Epicsuv-8.00 for array detectors Energy: 300 GeV – 10 PeV E-2.7, Hadrons (comp. HD4) E-2.6, Gamma (Crab-like) Data cuts: Zenith < 45o Core inside array Residual error < 1.0 m 1.25 p / any 4 30.0 < Sum_pFT <= 100.0 Representative energy: 4.2 TeV, Gamma 8.1 TeV, Hadrons Angular resolution 0.9o The Gamma/Hadron Separation • Data sample here (1999 ~ 2004, 10 * 109)

  8. R0 distributions & survival ratios Discrimination parameter for gamma and hadrons • Separation parameter • Global parameter • Mean distance to core • Virial distance of shower • Hit_max to core • Out core / All • Cluster parameter • Num_clus / Num_hit • Lateral distance of clus • Steepness of clus • Out_pixel / all_pixel • Image (FFT) parameter • 1st freq / DC • 2nd freq / DC • 1st freq / All • 2nd freq / All Hadron (MC) Gamma (MC) Real Data Syst ~= 5% where Ri is the distance between ith fitted detector and shower core in the shower-front plane.

  9. Quality factors: Gamma/hadron rejection and its quality factors • Rejection method • Excess to Bkgrd Ratio (E2BR): • E/B: E2BR before cut • E’/B’: E2BR after cut • Gamma survival ratio • Hadron survival ratio • Expectation: • 100% gamma: E = E’ • 100% hadron: E = E’’ • Where E’’ = ** E’ • Hypothesis Rejection: • 100% gamma by • Quality factor1 • 100% hadron by • Quality factor2 The key point is to compare the data sample before cut and after cut !!

  10. Back-Check by the Crab Nebula (The standard gamma-ray source) Data analysis by azimuth swapping ~ 0.0046 +/- 0.00085 Before Cut 100% gamma-ray excess, MC expected:0.0069 +/- 0.00012 (b) Bin size: 1.7deg * 1.7 deg ~ 0.0077 +/- 0.0012 After Cut (a) ~ 0.0031 +/- 0.00091 Comparison (a) (b) Hadron (100%) is rejected at 3.4 sigma;Data is consistent with gamma(100%) at 0.8 sigma.

  11. Investigations on Two Anisotropy Components: the Tail-In and Cygnus regions Data analysis by weighted azimuth swapping 3.0 deg smoothed Before Cut After Cut Comparison 100% CR excess assumption 100% gamma excess assumption

  12. Hints on the Tail-in and the Cygnus excesses Search Region (II) Large-scale anisotropy removed Gamma-like Comparison b = -5 100% CRs Ex. b = +5 b = +5 Comparison 100% Gam. Ex. b = -5 Search Region (I) Hadron-like Tail-In Cygnus

  13. Investigation on the Tail-In anisotropy component: Use it as the background source ( Is it CR !?) “Tail-In” Region (Independent) bin size: 10 deg * 12 deg

  14. ( Is it CR !?The GeV underground muon Exp. gives the answer is Yes !) ~ 0.0025 +/- 0.00014 Before Cut If 100% gamma-ray, reduced Excess to Background Ratio ~ 0.0025 +/- 0.00028 After Cut = 0.0014 +/- 0.0008, from the MC expectation. Comparison ~ 0.0011 +/- 0.00015 Gamma (100%) is rejected at 7.4 sigma;Data is consistent with hadron (100%) at 0.1 sigma.

  15. Investigation on the excess from the Cygnus region (gamma point source, diffuse gamma-ray emissions) 3.0 deg smoothed Before Cut After Cut b = -5 Off2 On Off1 b = +5 ( Cross + is MGRO J2019+37) +/- 3.0 deg After g/p cut, Excess to Background Ratio will be enhanced, if excess is from gamma. See next 

  16. Hadron Rejection:on & off the Galactic plane off1 on off2 Before Cut ~ 0.00065 +/- 0.00022 If 100% gamma, MC expected: 0.00120 +/- 0.00045 After Cut ~ 0.00198 +/- 0.00045 Comparison ~ 0.00133 +/- 0.00040 Cygnus Region Hadron (100%) is rejected at 3.4 sigma;Data is consistent with gamma (100%) at 1.8 sigma.

  17. Conclusive Remarks • The Crab excess is consistent with 100% gamma assumption at 0.8 sigma level, and 100% CRs assumption is rejected at 3.4 sigma level. (The CRs rejection is MC-independent). • The Tail-In region anisotropy is from CRs except the small region including the Crab Nebula.100% gamma excess assumption is rejected at 7.4 (3.5 [large-scale anisotropy removed]) sigma level.And 100% CR excess assumption is consistent at 0.1 (0.4 [large-scale anisotropy removed]) sigma level. • As the original excess from the Cygnus region in our search window (-4.0o < b < 2.0o, 72.0o < l < 78.0o) is at 3.3 sigma level, we cannot effectively judge it is from gamma-ray or CRs. CRs rejection is at about 3.4 sigma level.And the gamma-ray consistence is at about 1.8 sigma level. Due to the fluctuations, here the result shows the excess is over gamma-like. But the (diffuse) gamma-ray emission hypothesis is slightly favored. • Further improvement using multi-parameters is in progress.

  18. Appendix: background estimations • Global CR intensity fitting methods (I), (II) • Technique of time swapping (from Milagro) • Azimuth swapping method • Weighted azimuth swapping method

  19. Global CR intensity fitting method (I) Used in the published result Reference: M. Amenomori, et al., ApJ. V633, 1005 (2005)

  20. Global CR intensity fitting method (II) The background is estimated by weighted azimuth swapping A Technique of Data Shuffling 1) Auto event and background normalization 2) Auto azimuth correction in swapping M.C.

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