利用Cosmic-Ray月影精细调谐的Tibet-III空气簇射阵对蟹状星云的多Tev Gamma-Ray观测
Multi-Tev Gamma-Ray Observation from the Crab Nebula Using the Tibet-III Air Shower Array Finely Tuned by the Cosmic-Ray Moon's Shadow
摘要：
由533个闪烁探测器组成的Tibet-III空气簇射阵列自1999年以来一直在中国西藏羊八井成功运行。使用该阵列从1999年11月到2005年11月收集的数据集，我们获得了蟹状星云$γ$ -射线的能谱，用幂律表示为$(dJ/dE) = (2.09\pm0.32)\times10^{-12} (E/{\rm 3 TeV})^{-2.96\pm0.14} {\rm cm}^{-2} {\rm s}^{-1} {\rm TeV}^{-1}$，能量范围为1.7到40 TeV。这一结果与其他独立的$γ$射线观测成像空气切伦科夫望远镜是一致的。在本文中，我们仔细检查和调整的西藏-III阵列的性能使用数据的月球的阴影比较详细的蒙特卡罗模拟。由于地磁场的作用，阴影会移到月球视位置的西边，不过这种位移的程度取决于带正电的宇宙射线的初级能量。这一发现使我们能够估计从簇射大小确定初级能量的系统误差。在我们的实验中，该误差估计小于$\pm$ 12%。这种能量尺度估计是在地面宇宙线实验中的第一次尝试。系统指向误差也被估计为小于$0\fdg011$。月球阴影的亏损率和位置在每年$\pm$ 6%的统计误差内非常稳定。这保证了西藏-III台阵点状源观测的长期稳定性。这些系统误差在我们对蟹状星云的研究中得到了充分的考虑。
英文摘要：
The Tibet-III air shower array, consisting of 533 scintillation detectors, has been operating successfully at Yangbajing in Tibet, China since 1999. Using the dataset collected by this array from 1999 November through 2005 November, we obtained the energy spectrum of $γ$-rays from the Crab Nebula, expressed by a power law as $(dJ/dE) = (2.09\pm0.32)\times10^{-12} (E/{\rm 3 TeV})^{-2.96\pm0.14} {\rm cm}^{-2} {\rm s}^{-1} {\rm TeV}^{-1}$ in the energy range of 1.7 to 40 TeV. This result is consistent with other independent $γ$-ray observations by imaging air Cherenkov telescopes. In this paper, we carefully checked and tuned the performance of the Tibet-III array using data on the moon's shadow in comparison with a detailed Monte Carlo simulation. The shadow is shifted to the west of the moon's apparent position as an effect of the geomagnetic field, although the extent of this displacement depends on the primary energy positively charged cosmic rays. This finding enables us to estimate the systematic error in determining the primary energy from its shower size. This error is estimated to be less than $\pm$12% in our experiment. This energy scale estimation is the first attempt among cosmic-ray experiments at ground level. The systematic pointing error is also estimated to be smaller than $0\fdg011$. The deficit rate and position of the moon's shadow are shown to be very stable within a statistical error of $\pm$6% year by year. This guarantees the long-term stability of point-like source observation with the Tibet-III array. These systematic errors are adequately taken into account in our study of the Crab Nebula.
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