标题： Cyg X-1 X射线偏振的变化性 显示英文标题

标题： Variability of X-ray polarization of Cyg X-1

摘要： 我们展示了从2022年至2024年为期三年对典型黑洞X射线双星Cyg X-1进行的X射线、光学和射电偏振监测活动的结果。 Cyg X-1的X射线偏振使用成像X射线偏振探测器（IXPE）测量了13次，涵盖了硬态和软态两种光谱状态。 硬态下的X射线偏振度（PD）被发现为$\approx4.0\%$，大约是软态时的两倍，软态下约为$2.2\%$。 在两种状态下，偏振度均随能量显著增加。 此外，偏振度与光谱硬度之间的线性关系表明，偏振属性呈现逐渐且连续的演化，而非不同状态间偏振产生机制的突然变化。 偏振角度（PA）不受光谱状态的影响，并且与光子能量没有趋势关系。 X射线PA与射电喷流的方向以及光学和射电PA高度一致。 我们在硬态中发现了显著的轨道PA变化，将其归因于二元结构内X射线发射的散射。 未在周期$P_{\rm{so}}$= 294 天处发现PD或PA的显著超轨道变异性。我们还发现X射线和光学偏振之间无相关性；如果有，那么长期来看，X射线PD与射电PD之间存在反相关性。 显示英文摘要

摘要： We present the results of a three-year X-ray, optical, and radio polarimetric monitoring campaign of the prototypical black hole X-ray binary Cyg X-1, conducted from 2022 to 2024. The X-ray polarization of Cyg X-1 was measured 13 times with the Imaging X-ray Polarimetry Explorer (IXPE), covering both hard and soft spectral states. The X-ray polarization degree (PD) in the hard state was found to be $\approx4.0\%$, roughly twice as high as in the soft state, where it was around $2.2\%$. In both states, a statistically significant increase of PD with the energy was found. Moreover, a linear relation between PD and spectral hardness suggests a gradual and continuous evolution of the polarization properties, rather than an abrupt change of polarization production mechanism between states. The polarization angle (PA) was independent of the spectral state and showed no trend with the photon energy. The X-ray PA is well aligned with the orientation of the radio jet, as well as the optical and radio PAs. We find significant orbital changes of PA in the hard state, which we attribute to scattering of X-ray emission at intrabinary structure. No significant superorbital variability in PD or PA was found at the period $P_{\rm{so}}$ = 294 d. We also find no correlation between the X-ray and optical polarization; if any, there is a long-term anti-correlation between the X-ray PD and the radio PD.