1. 1 Observation of TeV Gamma Rays with the Tibet Air Shower Array and Future Prospects ICRR, University of Tokyo Kazumasa Kawata For the Tibet AS  Collaboration

2. 2 M.Amenomori(1), X.J.Bi(2), D.Chen(3), S.W.Cui(4), Danzengluobu(5), L.K.Ding(2), X.H.Ding(5), C.Fan(6), C.F.Feng(6), Zhaoyang Feng(2), Z.Y.Feng(7), X.Y.Gao(8), Q.X.Geng(8), H.W.Guo(5), H.H.He(2), M.He(6), K.Hibino(9), N.Hotta(10), Haibing Hu(5), H.B.Hu(2), J.Huang(2,3), Q.Huang(7), H.Y.Jia(7), F.Kajino(11), K.Kasahara(12), Y.Katayose(13), C.Kato(14), K.Kawata(3), Labaciren(5), G.M.Le(15), A.F.Li(6), J.Y.Li(6), Y.-Q.Lou(16), H.Lu(2), S.L.Lu(2), X.R.Meng(5), K.Mizutani(12,17), J.Mu(8), K.Munakata(14), A.Nagai(18), H.Nanjo(1), M.Nishizawa(19), M.Ohnishi(3), I.Ohta(20), T.Ouchi(9), S.Ozawa(12), J.R.Ren(2), T.Saito(21), T.Y.Saito(22), M.Sakata(11), T.K.Sako(3), M.Shibata(13), A.Shiomi(23), T.Shirai(9), H.Sugimoto(24), M.Takita(3), Y.H.Tan(2), N.Tateyama(9), S.Torii(12), H.Tsuchiya(25), S.Udo(12), B.Wang(2), H.Wang(2), X.Wang(3), Y.Wang(2), Y.G.Wang(6), H.R.Wu(2), L.Xue(6), Y.Yamamoto(11), C.T.Yan(3), X.C.Yang(8), S.Yasue(26), Z.H.Ye(15), G.C.Yu(7), A.F.Yuan(5), T.Yuda(9), H.M.Zhang(2), J.L.Zhang(2), N.J.Zhang(6), X.Y.Zhang(6), Y.Zhang(2), YiZhang(2), Zhaxisangzhu(5) and X.X.Zhou(7) The Tibet AS  Collaboration (1) Dep. of Phys., Hirosaki Univ., Hirosaki, Japan (2) Key Lab. of Particle Astrophys., IHEP, CAS, Beijing, China (3) ICRR., Univ. of Tokyo, Kashiwa, Japan (4) Dep. of Phys., Hebei Normal Univ., Shijiazhuang, China (5) Dep. of Math. and Phys., Tibet Univ., Lhasa, China (6) Dep. of Phys., Shandong Univ., Jinan, China (7) Inst. of Modern Phys., South West Jiaotong Univ., Chengdu, China (8) Dep. of Phys., Yunnan Univ., Kunming, China (9) Fac. of Eng., Kanagawa Univ, Yokohama, Japan (10) Fac. f of Educ., Utsunomiya Univ., Utsunomiya, Japan (11) Dep of Phys., Konan Univ., Kobe, Japan (12) Advanced Research Inst. for Sci. and Engin., Waseda Univ., Tokyo, Japan (13) Fac. of Eng., Yokohama National Univ., Yokohama, Japan (14) Dep. of Phys., Shinshu Univ., Matsumoto, Japan (15) Center of Space Sci. and Application Research, CAS, Beijing, China (16) Phys. Dep. and Tsinghua Center for Astrophys., Tsinghua Univ., Beijing, China (17) Dep. of Phys., Saitama Univ., Saitama, Japan (18) Advanced Media Network Center, Utsunomiya University, Utsunomiya, Japan (19) National Inst. of Info., Tokyo, Japan (20) Sakushin Gakuin University, Utsunomiya, Japan (21) Tokyo Metropolitan College of Industrial Tech., Tokyo, Japan (22) Max-Planck-Institut fuer Physik, Muenchen, Germany (23) College of Industrial Technology, Nihon University, Narashino, Japan (24) Shonan Inst. of Tech., Fujisawa, Japan (25) RIKEN, Wako 351-0198, Japan (26) School of General Educ.,Shinshu Univ., Matsumoto, Japan

3. 3 Tibet-III Air Shower (AS) Array  Number of Scinti. Det.0.5 m 2 x 789  Effective Area for AS~37,000 m 2  Energy region~TeV - 100 PeV  Angular Resolution~0.4 @10 TeV (Gamma rays) ~0.2 @100 TeV  Energy Resolution~70% @10 TeV (Gamma rays)~40% @100TeV  F.O.V.~2 sr 4,300 m a.s.l. (606 g/cm 2 )

4. 4 Constant fitting -0.0034 o 0.011 o + Systematic pointing error < 0.01 o Absolute Energy Scale error –4.4% +- 7.9%stat +- 8%sys Energy dependence of Displacements Caused by Geomagnetic field Verification  Absolute energy scale  Angular resolution  Pointing error Cosmic Ray Energy Calib. by the Moon’ Shadow

5. 5 Energy Spectrum of the Crab Nebula 90%CL Centered at Crab position ICRC2007, Mexico Submitted to ApJ

6. 6 0 360 R.A. (deg) Amenomori et al, Science, 314, 439 (2006) Cygnus region Tail-InLoss-Cone MGRO J2019+37 (800 mCrabs @ 20TeV) MGRO J2031+41 (900 mCrabs @ 20TeV) Cygnus region Cosmic-ray/Gamma-ray anisotropy Anisotropy map 0.9 deg. radius A.A.Abdo et al., ApJ, 664 L91 (2007) Window size: 5 deg. radius

7. 7  Future Plan Tibet muon detector (MD) project & Prototype MD in Tibet

8. 8 MAGIC VERITAS HESS Present Status of the TeV  Ray Astronomy 90%CL Antoni et al, ApJ, 608, 865 (2004) Atkins et al, ApJ, 608, 680 (2004) Amenomori et al, ApJ, 633, 1005 (2005) McKay et al, ApJ, 417, 742 (1993) Improve sensitivity to gamma rays in 100 TeV region (10 – 1000 TeV) Number of muons in air showers （ <100m from shower core, 4300m a.s.l. ） 100TeV proton ~50 100TeV gamma ~1

9. 9 Tibet Muon Detector (MD) Array 7.2m x 7.2m x 1.5m depth Water cell 20”  PMT x 2 (HAMAMATSU R3600) Underground 2.5m ( ~515g/cm 2 ~19X 0 ) Material:  Concrete pool  White paint 192 detctors Total ~10,000 m 2 We will count the number of muons by an air shower trigger Full Monte Carlo Simulation extends AS to ~83,000m 2 MD ~10,000m 2

10. 10 Muon Number vs. Shower Size (Simulation)  : Sum of particle density by all scintillation det. >> Shower Size  N PE :Sum of photoelectrons by all muon det. >> Muon number (Threshold of ＭＤ N PE >10 p.e.)  ( Shower Size)  N PE  ( Muon Number)  10TeV100TeV1000TeV 20% 50% 80% (gamma) 0 (~10TeV) 0 (~100TeV) Gamma CR 99.8% Rejection ~99.99% Rejection CR Gamma 0  N PE  ( Muon Number)  

11. 11 Future Sensitivity （ 5  or 10 events ）

12. 12 52m 2 x 2 Prototype Muon Detector in Tibet Construction starts from Sep. 2007 Data taking starts from Dec. 2007 Construction feasibility in Tibet Development of MC simulation  observation above several 100 TeV

13. 13 September, 2007 – Start construction CementConcrete mixer On Sep. 1st, start constructionSep. 4 th - finish almost digging

14. 14 Sep. 13 th - finish substructureOct. 5 th – Steel bars, forms Oct. 15 th – concrete worksOct 20 th – remove forms September ~ October

15. 15 16 November, 2007 Prototype Muon Detector

16. 16 Prototype Muon Detector after covering

17. 17 White paint Pouring very clear well-waterFilled up water 1.5 m in depth Inside of the MD Clear underground water from a nearby well 20”  PMT x 3: (Normal gain x 2, 1/100 gain x 1 for test) Water depth : 1.5 m

18. 18 Summary Tibet MD Project ~83,000 m 2 Air Shower array + ~10,000 m 2 Water Cerenkov Muon Detector array (~7M US$) Gamma-ray astrophysics in the 100 TeV region (10 – 1000 TeV) – Diffuse and point-like sources – Study on the maximum energy of gamma rays – Origin and acceleration limit of cosmic rays (p 0 decay /IC) Sensitivity (based on detailed simulation) – BG rejection power 99.8% rejected (50% gamma-ray events retained) @ 10 TeV 99.99% rejected (83% gamma-ray events retained) @ 100 TeV – Improve by an order of magnitude compared with the present Tibet AS array >~10 TeV Surpass existing IACTs >~40 TeV Surpass future plans of IACTs Prototype MD (52 m 2 x 2 cells) – successfully completed – data taking started in Dec. 2007 – in good agreement with MC simulation