在70-300 keV能量范围内空间科学用细间距CdTe-based硬X射线偏振计性能
Fine pitch CdTe-based Hard-X-ray polarimeter performance for space science in the 70-300 keV energy range
摘要：
X射线天体物理源几乎完全通过成像，光谱和定时分析来表征。然而，由于中子星或黑洞中存在的某些辐射机制仍不清楚，因此需要更多的观测参数。偏振测量将在区分不同的X射线发射模型中发挥关键作用。这种能力成为下一代高能空间提案的强制性要求。我们已经开发了一种基于CdTe的细间距成像光谱仪，Caliste，能够响应这些新的要求。在580微米的间距和1 keV的能量分辨率为60 keV时，我们能够准确地重建光子的入射通量的偏振角和偏振分数，这些光子在晶体内康普顿扩散后散射90°。由于其在成像和光谱测定方面的高性能，Caliste成为高能偏振测量的强大设备。在本文中，我们提出了这种测量的原理和获得的结果：一方面，我们描述了我们已经开发的模拟工具，以预测在50-300 keV的能量范围内的极化性能。另一方面，我们比较模拟结果与实验数据在ESRF ID 15 A（欧洲同步辐射设施）使用单能量偏振光束之间的35和300千电子伏的调整。我们表明，它是可能的，与此检测器，以确定高精度的偏振参数（方向和分数）为不同的照射条件。应用一个明智的能源选择我们的数据集，我们达到了显着的灵敏度水平，其特征在于在200-300千电子伏范围内的最佳品质因数为0.78。我们还评估了我们的设备在70千电子伏，其中硬X射线镜已经可用的灵敏度;测得的Q因子为0.64，在70千电子伏。
英文摘要：
X-rays astrophysical sources have been almost exclusively characterized through imaging, spectroscopy and timing analysis. Nevertheless, more observational parameters are needed because some radiation mechanisms present in neutrons stars or black holes are still unclear. Polarization measurements will play a key role in discrimination between different X-ray emission models. Such a capability becomes a mandatory requirement for the next generation of high-energy space proposals. We have developed a CdTe-based fine-pitch imaging spectrometer, Caliste, able to respond to these new requirements. With a 580-micron pitch and 1 keV energy resolution at 60 keV, we are able to accurately reconstruct the polarization angle and polarization fraction of an impinging flux of photons which are scattered by 90° after Compton diffusion within the crystal. Thanks to its high performance in both imaging and spectrometry, Caliste turns out to be a powerful device for high-energy polarimetry. In this paper, we present the principles and the results obtained for this kind of measurements: on one hand, we describe the simulation tool we have developed to predict the polarization performances in the 50-300 keV energy range. On the other hand, we compare simulation results with experimental data taken at ESRF ID15A (European Synchrotron Radiation Facility) using a mono-energetic polarized beam tuned between 35 and 300 keV. We show that it is possible with this detector to determine with high precision the polarization parameters (direction and fraction) for different irradiation conditions. Applying a judicious energy selection to our data set, we reach a remarkable sensitivity level characterized by an optimum Quality Factor of 0.78 in the 200-300 keV range. We also evaluate the sensitivity of our device at 70 keV, where hard X-ray mirrors are already available; the measured Q factor is 0.64 at 70 keV.
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