气体像素探测器的低能偏振灵敏度
Low energy polarization sensitivity of the Gas Pixel Detector
摘要：
已提议将基于气体像素探测器的X射线光电偏振计纳入许多即将进行的空间飞行任务，以填补从第一次（迄今为止唯一一次）对天体物理源的偏振X射线发射进行阳性测量以来约30年的空白。估计灵敏度的电流原型峰值的能量约为3千电子伏，但缺乏现成的极化源，在这个能量范围内，阻止了检测器极化性能的测量。在本文中，我们提出的气体像素探测器偏振灵敏度的测量在几个千电子伏的能量和新的，轻，紧凑和可运输的偏振源，设计和建造这一目标。偏振光子是由X射线管产生的非偏振辐射通过布拉格衍射在近45度产生的。马赛克石墨和平面铝晶体的就业允许生产几乎完全偏振的光子在2.6，3.7和5.2千电子伏的非偏振连续或线发射的衍射。在这些能量下测量的气体像素检测器的调制因子与从Monte Carlo软件获得的估计值非常一致，该软件迄今为止用于驱动仪器的开发和估计其低能量灵敏度。在本文中，我们提出了出色的偏振性能的气体像素探测器的能量峰值灵敏度是预期的。这些测量结果不仅支持了我们先前的高灵敏度的主张，而且证实了天体物理X射线光电偏振测量的可行性。
英文摘要：
An X-ray photoelectric polarimeter based on the Gas Pixel Detector has been proposed to be included in many upcoming space missions to fill the gap of about 30 years from the first (and to date only) positive measurement of polarized X-ray emission from an astrophysical source. The estimated sensitivity of the current prototype peaks at an energy of about 3 keV, but the lack of readily available polarized sources in this energy range has prevented the measurement of detector polarimetric performances. In this paper we present the measurement of the Gas Pixel Detector polarimetric sensitivity at energies of a few keV and the new, light, compact and transportable polarized source that was devised and built to this aim. Polarized photons are produced, from unpolarized radiation generated with an X-ray tube, by means of Bragg diffraction at nearly 45 degrees. The employment of mosaic graphite and flat aluminum crystals allow the production of nearly completely polarized photons at 2.6, 3.7 and 5.2 keV from the diffraction of unpolarized continuum or line emission. The measured modulation factor of the Gas Pixel Detector at these energies is in good agreement with the estimates derived from a Monte Carlo software, which was up to now employed for driving the development of the instrument and for estimating its low energy sensitivity. In this paper we present the excellent polarimetric performance of the Gas Pixel Detector at energies where the peak sensitivity is expected. These measurements not only support our previous claims of high sensitivity but confirm the feasibility of astrophysical X-ray photoelectric polarimetry.
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