Study of Ultra-high Energy Cosmic Rays at Tibetan Highlands

1989年，中国科学家在羊八井（4,300米）开始了一项新的寻找天体γ射线点源的空气簇射实验。S. L.，90.5^东经，30.1^北纬。目前的阵列由49个闪烁计数器组成，用于快速计时（FT），每个闪烁计数器的面积为0.5 m^2，并以15 m的间距放置在网格图案中。其他16个密度计数器围绕FT计数器阵列，以选择其核心落入阵列内的簇射。实验采用TKO和CAMAC系统，由32位微机控制。数据记录在一个8毫米的录像带上，容量约为2 GB。配备了稳定度<54 μ s/月的铷钟，可精确接收空气簇射的到达时间。从1990年6月开始全面展开的这项工作，目前正以约20 Hz的高触发率连续进行，寻找能量低于100 TeV的γ射线点源。目前，只有我们的阵列可以检测到s ...更多信息 由于观测点位于高空，因此有效地抑制了这种低能γ射线的辐射，并利用实验数据对该阵列的性能进行了检验，与蒙特卡罗模拟结果进行了比较。这表明，在100 TeV的能量下，可以用大约0.5 μ m的角分辨率确定空气簇射的到达方向。对于100 TeV的伽马射线，能量分辨率估计为约30%。可检测的簇射能量估计为约20 TeV，并且对于伽马射线簇射，非偏置能量对应于约40 TeV。我们的实验在目前世界上运行的众多空气簇射阵中具有独特的特点，能够观测到几十TeV能区的γ射线点源，这是地面上的反射镜和阵列实验所无法达到的，我们还需要运行该阵列至少一年以上来检验Cyg是否存在。X-3和其他点源候选者确实稳定地或不稳定地发射高能伽马射线。第一个结果将在今年秋天公布。少

A new air shower experiment, aiming to search for celestial gamma ray point sources, has been started from 1989 with Chinese scientists at Yangbajing (4,300m a. s. l., 90.5^ﾟE and 30.1^ﾟN) in Tibet. The present array consists of 49 scintillation counters for fast timing (FT), each of which has an area of 0.5 m^2 and is placed in a grid pattern with a spacing of 15 m. Other 16 density counters surround the FT counter array to select the showers whose core fall inside the array. The TKO and CAMAC system, controlled by a 32 bit micro-computer, is employed in this experiment. The data are recorded on a 8 mm video tape of about 2 GB capacity. A Rb clock with a stability of <54 mus/month is equipped to receive the arrival time of air showers precisely. The operation, atarted fully from June of 1990, is now successively continued with a high trigger rate of about 20 Hz to search for gammaray point sources in the energy region lower than 100 TeV. For the time being, only our array can detect s … More uch rather low energy gamma-rays effectively, since the observation site is located at high altitude.The performance of the present array was examined by using the experimental data, comparing those with a Monte Carlo simulation. This shows that the arrival direction of air showers can be determined with an angular resolution of about 0.5^ﾟ at 100 TeV. Also the energy resolution is estimated to be about 30% for a 100 TeV gamma ray. The detectable shower energy is estimated to be about 20 TeV, and the non-bias energy corresponds to about 40 TeV for gamma ray showers. Our experiment is therefore considered to have a distinctive feature among a lot of air shower arrays working now in the world, giving a capability of observing gamma ray point sources in the several 10 TeV energy region where both of mirror and array experiment on the ground are inaccessible.We still need to operate this array at least for more than one year to examine whether Cyg. X-3 and other point source candidates really emit high energy gamma rays steadily or not. The first result will be given in this fall. Less