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Temperature structure in the Perseus cluster core observed with Hitomi

机译：用瞳观察英仙座星团核心的温度结构

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The present paper explains the temperature structure of X-ray emitting plasma in the core of the Perseus cluster based on 1.8–20.0?keV data obtained with the Soft X-ray Spectrometer (SXS) on board the Hitomi Observatory. A series of four observations was carried out, with a total effective exposure time of 338?ks that covered a central region of ～7? in diameter. SXS was operated with an energy resolution of ～5?eV (full width at half maximum) at 5.9?keV. Not only fine structures of K-shell lines in He-like ions, but also transitions from higher principal quantum numbers were clearly resolved from Si through Fe. That enabled us to perform temperature diagnostics using the line ratios of Si, S, Ar, Ca, and Fe, and to provide the first direct measurement of the excitation temperature and ionization temperature in the Perseus cluster. The observed spectrum is roughly reproduced by a single-temperature thermal plasma model in collisional ionization equilibrium, but detailed line-ratio diagnostics reveal slight deviations from this approximation. In particular, the data exhibit an apparent trend of increasing ionization temperature with the atomic mass, as well as small differences between the ionization and excitation temperatures for Fe, the only element for which both temperatures could be measured. The best-fit two-temperature models suggest a combination of 3 and 5?keV gas, which is consistent with the idea that the observed small deviations from a single-temperature approximation are due to the effects of projecting the known radial temperature gradient in the cluster core along the line of sight. A comparison with the Chandra/ACIS and the XMM-Newton/RGS results, on the other hand, suggests that additional lower-temperature components are present in the intracluster medium (ICM), but not detectable with Hitomi/SXS giving its 1.8–20?keV energy band.
机译：本文基于由Hitomi天文台的软X射线光谱仪（SXS）获得的1.8–20.0？keV数据，解释了英仙座星团核心中发射X射线等离子体的温度结构。进行了一系列的四次观测，总有效暴露时间为338ks，覆盖了〜7？的中心区域。在直径上。 SXS的能量分辨率为5.9？keV时，能量分辨率为〜5？eV（半峰全宽）。从Si到Fe，不仅解析出He类离子中K壳线的精细结构，而且从更高的主量子数跃迁也得到了清晰的解析。这使我们能够使用Si，S，Ar，Ca和Fe的线比执行温度诊断，并提供对英仙座星团中激发温度和电离温度的首次直接测量。观察到的光谱在碰撞电离平衡中由单温度热等离子体模型粗略地再现，但是详细的线比率诊断显示与该近似值略有偏差。特别地，数据显示出随着原子质量电离温度升高的明显趋势，以及Fe的电离温度和激发温度之间的微小差异，Fe是唯一可以测量两个温度的元素。最佳拟合的两个温度模型建议使用3？keV气体和5？keV气体的组合，这与以下想法相一致：观察到的与单温度近似值的小偏差是由于投影已知径向温度梯度的影响所致。集群核心沿视线。另一方面，与Chandra / ACIS和XMM-Newton / RGS结果的比较表明，簇内介质（ICM）中存在其他低温成分，但Hitomi / SXS不能检测出其1.8–20 ？keV能带。

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