NuSTAR和Swift联合观测的中子星X射线双星4U~1728--34：岛和低香蕉态的盘反射
NuSTAR and Swift joint view of neutron star X-ray binary 4U~1728--34 : Disc reflection in the island and lower banana states
摘要：
分析了2013年10月1日和3日观测到的环礁型中子星（NS）X射线双星4U~1728--34的两个同步\nustar{}和\swift{}数据。根据功率密度谱、硬度比和色-色图，我们推断第一和第二个观测值分别属于岛态和下香蕉态。在岛态期间，观察到$\sim4.53$ Hz的低频准周期振荡（LQPO）以及四个I型X射线爆发（每个$\sim 10-15$ s持续时间）。岛态和低香蕉态的源X射线光度分别为$L_{X}= 1.1$和$1.6\times10^{37}$ erg s $^{-1}$，对应于爱丁顿光度的$\sim 6\%$和$\sim 9\%$。组合爆发光谱很好地代表了一个黑体的特征温度$2.22\pm0.05\kev$和$9.87\pm1.86$公里的黑体半径，这是符合典型的半径的中子星。在能量带$1-79\kev$的持续的能量谱从两个观测很好地描述了从NS表面的热发射（$kT_{bb}\simeq1-2.5\kev$），热种子光子从热的边界层/日冕和强反射组件从吸积盘的康普顿发射。我们在$5-8 \kev$波段探测到宽的铁谱线，在$15-30 \kev$波段探测到反射峰。这些特征由{ \tt relxill}反射模型很好地建模。通过联合谱拟合，我们将双星系统的倾角和内盘半径分别约束为$22\degree-40\degree$和$(2.8-4.3)\times R_{ISCO}$。根据圆盘的内径，我们估计磁场为$(3.3-6.5)\times10^{8}$高斯。
英文摘要：
We analyze two simultaneous \nustar{} and \swift{} data of the Atoll type neutron star (NS) X-ray binary 4U~1728--34 observed on 1 and 3 October, 2013. Based on power density spectra, hardness ratio and colour-colour diagram, we infer that the first and second observations belong to the island state and lower banana state, respectively. During island state, a low-frequency quasi-periodic oscillation (LFQPO) at $\sim4.53$ Hz is observed along with four type-I X-ray bursts ($\sim 10-15$ s duration each). The X-ray luminosity of the source during the island and lower banana states are found to be $L_{X}= 1.1$ and $1.6\times10^{37}$ erg s$^{-1}$, respectively which correspond to $\sim 6\%$ and $\sim 9\%$ of the Eddington luminosity. The combined burst spectrum is well represented by a blackbody with a characteristic temperature of $2.22\pm0.05\kev$ and the blackbody radius of $9.87\pm1.86$ km which is consistent with the typical radius of the neutron star. The persistent energy spectra from both observations in the energy band $1-79\kev$ are well described with thermal emission from the NS surface ($kT_{bb}\simeq1-2.5\kev$), Comptonized emission of thermal seed photons from the hot boundary layer/corona and the strong reflection component from the accretion disc. We detect a broad Iron line in the $5-8 \kev$ band and reflection hump in the $15-30 \kev$ band. These features are well modelled by the {\tt relxill} reflection model. From joint spectral fitting, we constrain the inclination angle of the binary system and inner disc radius to be $22\degree-40\degree$ and $(2.8-4.3)\times R_{ISCO}$, respectively. From inner disc radius, we estimate the magnetic field to be $(3.3-6.5)\times10^{8}$ Gauss.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
