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In-situ measurements of whole-dish reflectivity for VERITAS
Astroparticle Physics ( IF 3.5 ) Pub Date : 2021-03-01 , DOI: 10.1016/j.astropartphys.2020.102556
S. Archambault , G. Chernitsky , S. Griffin , D. Hanna

The VERITAS array is a set of four imaging atmospheric Cherenkov telescopes (IACTs) sensitive to gamma rays at energies between 85 GeV and 30 TeV. 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 aging can be monitored. A CCD camera attached near the centre of the dish simultaneously acquires an image of both a target star and its reflection on a target 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 placed in front of the CCD camera, allowing to measure the reflectivity as a function of wavelength. We present initial results obtained with the VERITAS telescopes during 2012.

中文翻译:

VERITAS 全盘反射率的原位测量

VERITAS 阵列是一组四个成像大气切伦科夫望远镜 (IACT),对能量在 85 GeV 和 30 TeV 之间的伽马射线敏感。每个望远镜都基于一个直径为 12 米的镶嵌镜子,它反射来自伽马射线引起的空气淋浴的光,在由 499 个光电倍增管组成的像素化“相机”上形成图像。图像亮度是伽马射线能量的主要量度,因此了解镜面反射率很重要。我们在这里描述了一种由 MAGIC 合作成员首创的方法,可以快速、定期地测量整盘反射率,从而可以监测老化的影响。安装在培养皿中心附近的 CCD 相机同时获取目标恒星及其在 Spectralon 目标上的反射图像,Spectralon 是一种高反射材料,放在望远镜的焦点上。由 CCD 记录的它们的亮度比以及几何因素提供了盘反射率的估计,几乎没有系统误差。滤光轮放置在 CCD 相机的前面,可以测量作为波长函数的反射率。我们展示了 2012 年使用 VERITAS 望远镜获得的初步结果。
更新日期:2021-03-01
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