T. Niwa

Northern Sky Galactic Cosmic Ray Anisotropy between 10 and 1000 TeV with the Tibet Air Shower Array

We report on the analysis of the 10−1000 TeV large-scale sidereal anisotropy of Galactic cosmic rays (GCRs) with the data collected by the Tibet Air Shower Array from 1995 October to 2010 February. In this analysis, we improve the energy estimate and extend the decl. range down to −30◦. We find that the anisotropy maps above 100 TeV are distinct from that at a multi-TeV band. The so-called tail-in and loss-cone features identified at low energies get less significant, and a new component appears at ∼ 100 TeV. The spatial distribution of the GCR intensity with an excess (7.2σ pre-trial, 5.2σ post-trial) and a deficit (−5.8σ pre-trial) are observed in the 300 TeV anisotropy map, in close agreement with IceCube’s results at 400 TeV. Combining the Tibet results in the northern sky with IceCube’s results in the southern sky, we establish a full-sky picture of the anisotropy in hundreds of TeV band. We further find that the amplitude of the first order anisotropy increases sharply above ∼ 100 TeV, indicating a new component of the anisotropy. All these results may shed new light on understanding the origin and propagation of GCRs.

Measurement of high energy cosmic rays by the new Tibet hybrid experiment

We have started a new hybrid air shower experiment at Yangbajing (4300 m a.s.l.) in Tibet in February 2014. This new hybrid experiment consists of the YAC-II comprised of 124 core detectors placed in the form of a square grid of 1.9 m spacing covering about 500 m2, the Tibet-III air shower array with the total area of about 50,000 m2 and the underground MD array consisting of 80 cells, with the total area of about 4,200 m2. This hybrid-array system is used to observe air showers of high energy celestial gamma-ray origin and those of nuclear-component origin. In this paper, a short review of the experiment will be followed by an overview on the current results on energy spectrum and chemical composition of CRs and test of hadronic interaction models.

Interplanetary Coronal Mass Ejection and the Sun's Shadow Observed by the Tibet Air Shower Array

We continuously observed the Sun’s shadow in 3 TeV cosmic-ray intensity with the Tibet-III air shower array since 2000. We find a clear solar-cycle variation of the deficit intensity in the Sun’s shadow during the periods between 2000 and 2009. The MC simulation of the Sun’s shadow based on the coronal magnetic field model does not well reproduce the observed deficit intensity around the solar maximum. However, when we exclude the transit periods during ICMEs towards to the Earth, the MC simulation shows better reproducibility. In the present paper, we report on the MC simulation and the analysis method of the Sun’s shadow observed by the Tibet-III array.

The Tibet AS+MD Project; status report 2017

We built a large (approximately 4,000 m**2) water　Cherenkov- type muon detector array under the existing Tibet air shower array at 4,300 m above sea level, to observe 10-1000 TeV gamma rays from cosmic-ray accelerators in our Galaxy with wide field of view at very low background level. A gamma-ray induced air shower has significantly less muons compared with a cosmic-ray induced one. Therefore, we can effectively discriminate between primary gamma rays and cosmic-ray background events by means of counting number of muons in an air shower event by the muon detector array. We make a status report on the experiment.

Solar magnetic field strength and the “Sun's Shadow”

The angular displacement of the center of the observed Suns shadow from the center of the optical solar disc tells us the information of average solar magnetic field strength in the space between the Sun and the Earth. We analyze the displacement of the Suns shadow observed in 5 ~ 240 TeV cosmic-ray intensity with the Tibet-III air shower array during 10 years between 2000 and 2009, and compare with the MC simulations based on the coronal magnetic field model and Parkers spiral interplanetary magnetic field model. We find that the observed North-South displacement is significantly larger than the prediction of simulations. This result uniquely suggests the underestimation of the average field strength between the Sun and the Earth in our model. In this work, we will report the actual solar magnetic field strength evaluated from the observed Suns shadow.

Search for gamma rays above 100 TeV from the Crab Nebula using the Tibet air shower array and the 100 m

M. Amenomori1, X. J. Bi2, D. Chen3, T. L. Chen4, W. Y. Chen2, S. W. Cui5, Danzengluobu4, L. K. Ding2, C. F. Feng6, Zhaoyang Feng2, Z. Y. Feng7, Q. B. Gou2, Y. Q. Guo2, H. H. He2, Z. T. He5, K. Hibino8, N. Hotta9, Haibing Hu4, H. B. Hu2, J. Huang2, H. Y. Jia7, L. Jiang2, F. Kajino10, K. Kasahara11, Y. Katayose12, C. Kato13, K. Kawata14, M. Kozai13, Labaciren4, G. M. Le15, A. F. Li16,6,2, H. J. Li4, W. J. Li2,7, C. Liu2, J. S. Liu2, M. Y. Liu4, H. Lu2, X. R. Meng4, T. Miyazaki13, K. Mizutani11,17, K. Munakata13, T. Nakajima13, Y. Nakamura13, H. Nanjo1, M. Nishizawa18, T. Niwa13, M. Ohnishi14, I. Ohta19, S. Ozawa11, X. L. Qian6,2, X. B. Qu20, T. Saito21, T. Y. Saito22, M. Sakata10, T. K. Sako14, J. Shao2,6, M. Shibata12, A. Shiomi23, T. Shirai8, H. Sugimoto24, M. Takita14, Y. H. Tan2, N. Tateyama8, S. Torii11, H. Tsuchiya25, S. Udo8, H. Wang2, H. R. Wu2, L. Xue6, Y. Yamamoto10, K. Yamauchi12, Z. Yang2, S. Yasue26, A. F. Yuan4, T. Yuda14, L. M. Zhai2, H. M. Zhang2, J. L. Zhang2, X. Y. Zhang6, Y. Zhang2, Yi Zhang2, Ying Zhang2, Zhaxisangzhu4, X. X. Zhou7