VERITAS全碟反射率的现场测量
In-situ measurements of whole-dish reflectivity for VERITAS
摘要：
VERITAS阵列是一套四个成像大气切伦科夫望远镜（IACT），对能量超过80 GeV的伽马射线敏感。每个望远镜都以一个直径12米的镶嵌镜为基础，反射伽马射线引起的空气簇射的光，在由499个光电倍增管组成的像素化“照相机”上形成图像。图像亮度是伽马射线能量的主要度量，因此了解镜面反射率是很重要的。我们在这里描述一种方法，由MAGIC合作的成员开创，快速，定期地测量全碟反射率，以便可以监测镜子老化的影响。一个安装在碟形天线中心附近的CCD相机同时获取恒星的图像和它在一个由Spectralon（一种高反射材料）制成的目标上的反射图像，该目标放置在望远镜的焦点处。由CCD记录的它们的亮度的比率以及几何因子提供了具有很少系统误差的碟形反射率的估计。滤光轮与CCD相机一起部署，允许测量作为波长的函数的反射率。我们介绍了自2014年以来使用VERITAS望远镜获得的结果。
英文摘要：
The VERITAS array is a set of four imaging atmospheric Cherenkov telescopes (IACTs) sensitive to gamma rays with energies above 80 GeV. Each telescope is based on a tessellated mirror, 12 metres in diameter, which reflects light from a gamma-ray-induced air shower to form an image on a pixellated `camera' comprising 499 photomultiplier tubes. The image brightness is the primary measure of the gamma ray's energy so a knowledge of the mirror reflectivity is important. We describe here a method, pioneered by members of the MAGIC collaboration, to measure the whole-dish reflectivity, quickly and regularly, so that effects of mirror aging can be monitored. A CCD camera attached near the centre of the dish simultaneously acquires an image of both a star and its reflection on a target made of Spectralon, a highly-reflective material, placed at the focus of the telescope. The ratio of their brightnesses, as recorded by the CCD, along with geometric factors, provides an estimate of the dish reflectivity with few systematic errors. A filter wheel is deployed with the CCD camera, allowing one to measure the reflectivity as a function of wavelength. We present results obtained with the VERITAS telescopes since 2014.
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