典型吸积盘冕源4U 1822-37的首次X射线偏振测量
The First X-Ray Polarimetry of the Typical Accretion Disk Corona Source 4U 1822-37
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中文总结 AI 辅助
研究利用IXPE和Swift-XRT观测ADC源4U 1822-37，发现其偏振度高于典型LMXB，软、硬辐射空间分布不同，偏振角旋转或源于散射几何不对称。
中文摘要 AI 辅助
我们报告了成像X射线偏振探测器（IXPE）对典型吸积盘冕（ADC）源4U 1822-37的首次观测，覆盖44个轨道周期，同时结合了Swift-XRT的同步观测数据。该源的偏振度（PD）被发现高于典型的低质量X射线双星（LMXB）值，且表现出显著的能量依赖性。在2-5 keV和5-8 keV能段内，PD保持恒定，平均值分别为5.6±0.8%和11.6±1.7%，二者差异显著（>3σ）。轨道相位分辨分析显示，在伴星食期间，2-5 keV能段的PD从显著非零值降至与零一致的水平，而偏振角（PA）保持不变；相比之下，5-8 keV能段的PD呈现微弱上升趋势，达到21.3±6.1%，且在食前PA表现出30°的周期性旋转。此外，在三天的时间尺度上，PA随中性吸收的增加旋转了40°。这些结果表明，2-8 keV能段的软、硬辐射可能起源于空间分布不同的区域，高PD意味着存在散射贡献，PA旋转可能与由凸起或团块引起的散射几何不对称性相关。
英文摘要
We report the first Imaging X-ray Polarimetry Explorer (IXPE) observations of the typical accretion disk corona (ADC) source 4U 1822-37, covering 44 orbital cycles, together with simultaneous Swift-XRT data. The polarization degree (PD) of this source is found to be higher than typical low-mass X-ray binary (LMXB) values and exhibits a significant energy dependence. Within the 2--5~keV and 5--8~keV bands, PD remains constant, with average values of \(5.6\pm0.8\%\) and \(11.6\pm1.7\%\), respectively, and the difference is significant (\(>3σ\)). Orbital phase-resolved analysis reveals that during the companion eclipse, the PD in the 2--5~keV band drops from a significantly non-zero value to a level consistent with zero, while the polarization angle (PA) remains unchanged. In contrast, the PD in the 5--8~keV band shows a marginal rising trend, reaching \(21.3\pm6.1\%\), and the PA exhibits a periodic rotation of \(30^\circ\) before the eclipse. In addition, the PA rotates by \(40^\circ\) with increasing neutral absorption on a three-day timescale. These results suggest that the soft and hard emission in the 2--8~keV band may originate from regions with different spatial distributions, with the high PD implying a scattering contribution. The PA rotation is likely linked to scattering geometry asymmetries caused by a bulge or clumps.
