AI 中文总结
研究利用IXPE等多卫星协同观测GX 13+1的周期性倾角，发现偏振特性随倾角显著变化，约束了其延展散射环境的几何结构，凸显X射线偏振数据的关键作用。
AI 中文摘要
中子星低质量X射线双星具有复杂的吸积几何结构，通常包含吸积盘冕或盘风。本文利用IXPE、NuSTAR和Swift-XRT的协同观测，对高度倾斜的倾角源GX 13+1开展研究，这是首次开展此类 campaign 以监测其周期性倾角。我们的分析显示，偏振特性随倾角发生显著变化：在倾角中心，偏振度达到最大值约9%（置信度大于8σ）；当从倾角过渡到后续的非倾角状态时，伴随有约60°的高度显著偏振角旋转。此外，倾角状态表现出能量依赖的偏振性。通过对周期性倾角期间的偏振进行建模，我们约束了散射介质的几何结构：在扁球形延展吸积盘冕（ADC）的场景下，需要赤道半径至少为极半径的1.5倍，光深τ约为0.3；或者，结果可建模为盘风散射，其最概然电子密度为1.3×10¹⁴ cm⁻³，开口角接近40°，对应光深约0.2。所得结果凸显了X射线偏振数据在揭示吸积盘周围延展散射环境几何结构方面的关键作用，增进了我们对中子星低质量X射线双星的理解。
英文摘要
Neutron star low-mass X-ray binaries feature complex accretion geometries, often including an accretion disk corona or disk winds. Here, a study of the highly inclined dipping source GX 13+1, using coordinated observations from the IXPE, NuSTAR, and Swift-XRT, is presented; this is the first time that such a campaign was conducted to monitor its periodic dip. Our analysis reveals significant variations in polarimetric properties tracking the dip. At the center of the dip, the polarization degree reaches a maximum of ${\sim}$9% (at more than $8σ$ confidence level). This is accompanied by a highly significant polarization angle rotation of roughly 60$^\circ$ when passing from the dip to the subsequent off-dip state. Furthermore, the dip state exhibits energy-dependent polarization. By modeling the polarization during the periodic dip, we constrain the geometry of the scattering medium. In the scenario of an oblate extended accretion disk corona (ADC), an equatorial radius at least 1.5 times its polar radius is needed with $τ{\sim}0.3$. Alternatively, the results can be modeled as scattering in a disk wind with a most probable electron density of $1.3\times10^{14}$ cm$^{-3}$ and an opening angle near 40$^\circ$, corresponding to an optical depth of ${\sim}0.2$. The obtained results highlight the crucial role of X-ray polarimetric data to unveil the geometry of the extended scattering environment surrounding the accretion disks, advancing our understanding of neutron star low-mass X-ray binaries.
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