AI 中文总结
研究 Z 型中子星低质量 X 射线双星的 X 射线偏振，利用 IXPE、NICER 和 NuSTAR 数据进行光谱偏振分析，发现连续 X 射线发射可用热吸积盘发射加康普顿化成分描述，各分支偏振度及偏振角有特点，且偏振信号与倾角等无相关性。
AI 中文摘要
IXPE 首次提供了 Z 型中子星低质量 X 射线双星（NS-LMXBs）沿其色-色图（CCDs）移动时的详细能量和时间分辨 X 射线偏振测量。这些源在沿水平分支移动时，在 2-8 keV 范围内可达到 NS-LXMBs 观测到的最高偏振。在之前的论文中，我们用 CCD 表征了 Z 源样本的光谱状态，并用与模型无关的分析估计了偏振。在此，我们使用 IXPE、NICER 和 NuSTAR 的数据对每个分支上的每个源进行详细的光谱偏振分析。所有源的连续 X 射线发射都可以用热吸积盘发射加上更硬的康普顿化成分来很好地描述。除了 GX 5-1 外，还观测到了反射特征，特别是相对论性展宽的铁线。对于大多数源和分支，X射线发射和偏振的主要贡献来自康普顿化：从水平分支（HB）移动到正常分支（NB），2-8 keV 波段的偏振度（PD）从约 6%变化到 3-4%，而在耀斑分支（FB）中，由于曝光时间较短，PD 受到的限制较宽松。这些 PD 值明显高于典型扩散或边界层配置的理论预期。盘的偏振通常较低（低于 3%），但仍高于在相应倾角下观测到的以电子散射为主的平面平行大气的预测值。此外，盘的偏振角（PA）似乎明显不对齐，且不垂直于康普顿化的偏振角。我们发现偏振信号与倾角之间没有相关性，也与整个 Z 轨迹上反射光子的贡献没有相关性。
英文摘要
IXPE has provided for the first time detailed energy- and time-resolved X-ray polarimetry of Z-type neutron star low-mass X-ray binaries (NS-LMXBs) as they move along their color-color diagrams (CCDs). These sources can reach the highest polarization observed for NS-LXMBs in the 2-8 keV range when they move along the horizontal branch. In a previous paper, we characterized the spectral state of a sample of Z-sources using the CCD and estimated the polarization with model-independent analysis. Here, we present detailed spectropolarimetric analysis for each source on each branch using data from IXPE, NICER, and NuSTAR. The continuum X-ray emission of all the sources is well described with a combination of thermal accretion disk emission plus a harder Comptonized component. In addition, reflection features, in particular the relativistically broadened Fe line, are observed for our sources, except GX 5-1. For most of the sources and branches, the main contribution to the X-ray emission and polarization is due to Comptonization: moving from the horizontal branch (HB) to the normal branch (NB), the polarization degree (PD) in the 2-8 keV band varies from about 6% to 3-4%, while the PD is loosely constrained in the flaring branch (FB), due to the shorter exposures. These PD values are significantly higher than theoretical expectations for typical spreading or boundary layer configurations. The polarization of the disk is generally lower (below 3%) but still higher than predictions for an electron scattering-dominated, plane-parallel atmosphere above the disk observed at the corresponding inclination. Moreover, the polarization angle (PA) of the disk seems to be significantly misaligned and not perpendicular to that of Comptonization. We find no correlation between the polarization signal and the inclination, nor with the contribution of reflected photons throughout the Z-track.
Comments14 pages, 4 figures, 8 tables
Journal refAstronomy & Astrophysics, 711, A208 (2026)
DOI：10.1051/0004-6361/202659608
