论文标题
朝4U 1820-30的热星际培养基：贝叶斯分析
The hot interstellar medium towards 4U 1820-30: a Bayesian analysis
论文作者
论文摘要
软X射线带中的高电离线通常与沿视线的星际热气体或源固有的光电离气体有关。在低质量X射线二进制4U 1820-30中，这些线的性质尚不清楚。我们表征了沿视线的离子气体朝向产生Mg XI，NE IX，Fe XVII，O VII和O VIII的X射线吸收系的源的电离气体。我们分析了使用RGS，HETG和LETG光谱仪进行的XMM-Newton和Chandra档案中的所有观察结果。高分辨率的光谱通过基于$ C $统计的标准X射线分析和贝叶斯参数推断对高分辨率光谱进行了准确检查。我们测试了两个物理模型，这些模型描述了碰撞电离或光电子平衡中的血浆。我们采用了贝叶斯模型与统计学的比较，比较了用于分析的模型的不同组合。}我们发现，这些线与星际介质中的热气是一致的，而不是与X射线二进制的固有气体相关联。我们的最佳拟合模型揭示了碰撞电离的血浆的存在，温度为$ t =（1.98 \ pm0.05）\ times10^6 $K。由于模型预测的低列密度，光电子化模型未能适合Fe XVII线路（以$6.5σ$检测到Fe XVII线路）。此外，二进制系统的低倾斜度可能是固定的电离气体固有的未检测的原因。}
High ionisation lines in the soft X-ray band are generally associated to either interstellar hot gas along the line of sight or to photoionised gas intrinsic to the source. In the low-mass X-ray binary 4U 1820-30, the nature of these lines is not well understood. We characterised the ionised gas present along the line of sight towards the source producing the X-ray absorption lines of Mg XI, Ne IX, Fe XVII, O VII, and O VIII. We analysed all the observations available for this source in the XMM-Newton and Chandra archives, taken with the RGS, HETG, and LETG spectrometers. The high-resolution grating spectra have been accurately examined through a standard X-ray analysis based on the $C$-statistic and through the Bayesian parameter inference. We tested two physical models which describe a plasma in either collisional ionisation or photoionisation equilibrium. We adopted the Bayesian model comparison to statistically compare the different combinations of the models used for the analysis.} We found that the lines are consistent with hot gas in the interstellar medium rather than being associated with the intrinsic gas of the X-ray binary. Our best-fit model reveals the presence of a collisionally ionised plasma with a temperature of $T=(1.98\pm0.05)\times10^6 $ K. The photoionisation model fails to fit the Fe XVII line (which is detected with a significance of $6.5σ$) due to the low column density predicted by the model. Moreover, the low inclination of the binary system is likely the reason for the non-detection of ionised gas intrinsic to the source.}
