Gamma-Ray Polarimetry: A New Window for the Nonthermal Universe
Gamma-Ray Polarimetry: A New Window for the Nonthermal Universe
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DOI：
10.1088/1538-3873/ab2a3a
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发表时间：
2019-06
影响因子：
3.5
通讯作者：
Cosmin Ilie
中科院分区：
文献类型：
--
作者：
Cosmin Ilie
在过去的几十年里，光子偏振测量领域取得了令人印象深刻的进展，特别是在硬X射线和软γ射线能量范围内。对于一些能量最高的天体物理源，如伽马射线暴（GRB）或耀变体，现在可以在能量低于对创建阈值的情况下测量线性偏振度。因此，一个新的窗口已经打开，以了解非热发射机制的确切性质，负责一些最具活力的现象在宇宙中。仍然有许多悬而未决的问题和积极的辩论，如轻子与强子的Blazar辐射模型或有序与伽马射线暴的随机场模型之间的区别。由于竞争模型预测了能量超过101 MeV的不同水平的线性光子偏振，该能带的伽马射线偏振测量可以提供额外的关键见解。然而，没有一个用于探测能量超过101 MeV的伽马射线的偏振仪被送入太空，因为探测器的灵敏度受到角分辨率迅速下降和多次库仑散射的严重限制。在过去几年中，提出了一系列旨在克服这些固有困难的建议和示范性文书，前景看好。第一部分简要回顾了γ射线偏振测量的历史和原理，强调了它所面临的挑战和成功之处：第二部分讨论了γ射线偏振和偏振测量，第三部分讨论了过去和现在成功测量天体物理源硬X射线和软γ射线线偏振的仪器;第4节概述了使用伽玛射线偏振测量可以解决的科学问题。第5节提供了总结和展望。
Over the past few decades, impressive progress has been made in the field of photon polarimetry, especially in the hard X-ray and soft gamma-ray energy regime. Measurements of the linear degree of polarization for some of the most energetic astrophysical sources, such as gamma-ray bursts (GRBs) or blazars, are now possible, at energies below the pair creation threshold. As such, a new window has been opened for understanding the exact nature of the nonthermal emission mechanisms responsible for some of the most energetic phenomena in the universe. There are still many open questions and active debates, such as the discrimination between leptonic versus hadronic models of emission for Blazars or ordered versus random field models for GRBs. Because the competing models predict different levels of linear photon polarization at energies above ∼1 MeV, gamma-ray polarimetry in that energy band could provide additional crucial insights. However, no polarimeter for gamma rays with energies above ∼1 MeV has been flown into space, as the sensitivity is severely limited by a quick degradation of the angular resolution and by multiple Coulomb scatterings in the detector. Over the past few years, a series of proposals and demonstrator instruments that aim to overcome those inherent difficulties have been put forth, and the prospects look promising. The paper is organized as follows: Section 1, briefly reviews the history and principles of gamma-ray polarimetry, emphasizing its challenges and successes; Section 2 is dedicated the discussion of gamma-ray polarization and polarimetry, and Section 3 discusses the past and current instruments with which measurements of linear polarization for hard X-rays and soft gamma rays were successfully obtained for astrophysical sources; Section 4 outlines the scientific questions that could be solved by using gamma-ray polarimetry measurements. A summary and outlook are provided in Section 5.