标题： X射线和射电波段对Z源GX 340+0的观测 II：正常分支中的X射线偏振 显示英文标题

标题： X-ray and Radio Campaign of the Z-source GX 340+0 II: the X-ray polarization in the normal branch

摘要： 我们利用成像X射线偏振探测器（IXPE）200 ks的观测，首次对中子星低质量X射线双星和Z源GX 340$+$0在正常分支（NB）进行了X射线偏振测量。 这次观测于2024年8月进行。 除了IXPE之外，我们还同时使用NICER、AstroSat、Insight-HXMT、ATCA和GMRT进行了观测，以研究X射线和无线电波段中的宽带光谱和时变特性。 在这次观测活动中，该源在IXPE观测期间描绘了一条完整的Z轨迹，但大部分时间处于正常分支。 我们在2-8 keV能量范围内测量了源的X射线偏振度（PD）为$1.22\pm0.25\%$，偏振角（PA）为$38\pm6^\circ$。 在正常分支中观察到的偏振度比水平分支（HB）弱，但方向一致。 源的偏振度随着能量的增加表现出微弱的增长趋势，而偏振角没有表现出能量依赖性。 联合光谱偏振建模与观测到的X射线偏振来自单一光谱成分（黑体辐射或康普顿化发射）的结果一致，而盘发射并未对X射线偏振做出贡献。 在水平分支期间，GMRT在1.26 GHz处的观测得到了一个初步检测，约为4.5$\pm$0.7 mJy；而在正常分支一天后的ATCA观测中，在5.5 GHz和9 GHz频带分别检测到了源的信号强度为0.70$\pm$0.05 mJy和0.59$\pm$0.05 mJy，这表明喷流结构随Z轨迹位置的变化而演变。 显示英文摘要

摘要： We present the first X-ray polarization measurement of the neutron star low-mass X-ray binary and Z-source, GX 340$+$0, in the normal branch (NB) using a 200 ks observation with the Imaging X-ray Polarimetric Explorer (IXPE). This observation was performed in 2024 August. Along with IXPE, we also conducted simultaneous observations with NICER, AstroSat, Insight-HXMT, ATCA, and GMRT to investigate the broadband spectral and timing properties in the X-ray and radio wavelengths. During the campaign, the source traced a complete Z-track during the IXPE observation but spent most of the time in the NB. We measure X-ray polarization degree (PD) of $1.22\pm0.25\%$ in the 2-8 keV energy band with a polarization angle (PA) of $38\pm6^\circ$. The PD in the NB is observed to be weaker than in the horizontal branch (HB) but aligned in the same direction. The PD of the source exhibits a marginal increase with energy while the PA shows no energy dependence. The joint spectro-polarimetric modeling is consistent with the observed X-ray polarization originating from a single spectral component from the blackbody or the Comptonized emission while the disk emission does not contribute towards the X-ray polarization. GMRT observations at 1.26 GHz during HB had a tentative detection at 4.5$\pm$0.7 mJy while ATCA observations a day later during the NB detected the source at 0.70$\pm$0.05 mJy and 0.59$\pm$0.05 mJy in the 5.5 & 9 GHz bands, respectively, suggesting an evolving jet structure depending on the Z-track position.