Study of Ultra-High Energy Cosmic Rays at Tibetan highlands

自1990年1月以来，中国科学家在西藏羊八井（4300米，90.5 E和30.1 N）上连续运行了西藏风淋阵。目前的阵列由65个闪烁探测器组成，它们被放置在间距为15m的晶格中。观测到的阵雨的模式能量估计约为7 TeV的伽马射线。通过观察宇宙射线在月球上的阴影，角分辨率得到了很好的检验。观测到的月影显著性为7.1sigma，对模式能量为7 TeV的阵雨的角分辨率估计为0.88，对模式能量为35的阵雨的角分辨率为0.52。影子向西偏移约0.16个<s:1>，这与地磁场效应的预期值相当。另一方面，太阳阴影在远离太阳的方向上被观测到，向西0.70，向南0.40。这种偏转被认为是由太阳和地球之间的磁场共同作用造成的。请注意，这些数据是在1990年至1993年期间太阳仍处于活跃阶段时获得的。这种对宇宙射线阴影的影响是首次观测到的，有望为我们提供关于太阳和行星际磁场大尺度结构及其时间变化的新信息。对包括蟹状星云、天鹅座X-3和天鹅座X-1在内的各种点源进行了对10 TeV伽马射线稳定发射的研究。对于Cyg X-3，在10 TeV和30 TeV下获得的通量极限远低于通过Kiel通量外推得到的水平。对于蟹状星云，没有过量的结果与THEMISTOCLE实验的阳性结果不一致，但与Whipple的新数据仍然一致。我们还搜索了活动星系核（agn）的伽马射线发射，这些活动星系核已被康普顿GRO上的EGRET报道为强大的伽马射线源。特别是最近的AGN，Markarian 421在10 TeV的结果是有趣的，对这个源的进一步观察将提供关于宇宙中红外光子场强度的新信息。目前的空气淋室阵列将在1994年扩大到3.7 *10^4 m^2的有效面积。该阵列将由221个闪烁探测器组成，它们被放置在一个间隔15米的晶格中。触发率约为250hz，死区时间小于30%。据估计，质子阵雨的模式能量约为5 TeV。这个新的阵列将在不久的将来提供关于行星际磁场以及宇宙射线加速的重要信息。少

The Tibet Air shower array at Yangbajing (4,300m, 90.5ﾟ E and 30.1ﾟ N) in Tibet has been operated continuously since January 1990, with Chinese scientists. The present array consists of 65 scintillation detectors which are placed in a lattice of 15m spacing. The mode energy of observed showers is estimated to be about 7 TeV for gamma rays. The angular resolution was well examined by observing the shadowing of cosmic rays by the moon. The moon shadow was observed with the significance of 7.1sigma and the angular resolution of the array is estimated to be 0.88ﾟ for showers with its mode energy 7 TeV and 0.52ﾟ for those with its mode energy 35 TeV.A small deflection of the shadow to the west by about 0.16ﾟ is comparable with that expected from the geomagnetic field effect.On the other hand, the sun shadow was observed in the direction away from the sun by 0.70ﾟ to the west and 0.40ﾟ to the south. This deflection is considered to be caused by the combined effect of the magnetic fields betw … More een the sun and the earth. Note that these data were taken when the sun was still in an active phase between 1990 and 1993. Such effect on the cosmic ray shadow is the first observation and is expected to bring us new information on the large scale structure of the solar and interplanetary magnetic field and its time variation.A search for steady emission of 10 TeV gamma rays has been made for various point sources including the Crab nebula, Cyg X-3 and Her X-1. For Cyg X-3, flux limits obtained at 10 TeV and 30 TeV for Cyg X-3 are far below the levels obtained by extrapolation of the Kiel flux. For the Crab nebula, the result obtained with no excess is inconsistent with the possitive results from the THEMISTOCLE experiment, while still being consistent with the Whipple new data. We also searched for gamma-ray emission from active galactic nuclei (AGNs) which have been reported to be poweful gamma-ray sources by EGRET on board the Compton GRO.In particular, the result for the nearest AGN,Markarian 421 at 10 TeV is interesting, and the further observation on this source will provide new information on the strength of infrared photon field in the universe. The present air shower array will be extended up to an effective area of 3.7 *10^4 m^2 in 1994. This array will consist of 221 scintilation detectors which are placed in a lattice of 15 m spacing. The trigger rate is taken to be about 250 Hz with a dead time less than 30 %. The mode energy for proton showers is estmated to be about 5 TeV.This new array will provide important information on the interplanetary magnetic field as well as acceleration of cosmic rays in the very near future. Less