标题： 平均类星体光谱的云模型 显示英文标题

标题： Cloud model of the mean quasar spectrum

摘要： 我们假设一种对电子散射光学厚（OTCM）的云层分布，它们对于吸收来说是中等光学薄的，并将其视为Laor等人（1997年）的平均类星体光谱模型。我们表明该模型对电离参数$\xi$的值特别敏感，并且对于$\xi \sim 500$，该模型能很好地再现光学/紫外/X射线平均类星体光谱，这与基于铁$K_{\alpha}$线能量的电离参数估计一致。我们不能排除同步辐射作为主要辐射的来源，但我们更倾向于这样的模型，即硬X射线辐射是由于软光子在中心热介质中的康普顿散射，该介质被冷却云层包围。在这种模型中，云通常位于$\sim 12 R_{Schw}$的距离处，覆盖因子约为0.88，热等离子体的半径为$\sim 9 R_{Schw}$。该模型将光学/紫外辐射解释为主要来自云的暗面，而软X射线辐射则是由于照射面的反射。因此，这些波段中预期存在原子特征，尽管它们在观测数据中几乎不存在。与云运动相关的动力学效应会影响这些特征，但不会消除它们。为了模拟平均类星体光谱所需的初级辐射水平太低，无法正确再现铁K$_{\alpha}$线的等值宽度，但更详细的计算可能会解决这个问题。 显示英文摘要

摘要： We assume a distribution of clouds optically thick for electron scattering (OTCM) which are moderately optically thin for absorption and we consider them as a model of the mean quasar spectrum of Laor et al. (1997). We show that the model is particularly sensitive to the value of the ionization parameter $\xi$ and that for $\xi \sim 500$ the model well reproduces the optical/UV/X-ray mean quasar spectrum, in agreement with the estimates of the ionization parameter based on the energy of the iron $K_{\alpha}$ line. We cannot definitively reject synchrotron emission as a source of primary radiation but we favor the model in which the hard X-ray emission is produced by Compton scattering of soft photons in a central hot medium surrounded by cool clouds. In such a model clouds are located typically at the distance of $\sim 12 R_{Schw}$, with the covering factor about 0.88 and the radius of hot plasma is $\sim 9 R_{Schw}$. The model explains optical/UV emission as predominantly due to the dark sides of the clouds and the soft X-ray emission as due to the reflection by the irradiated sides of the clouds. Therefore, atomic features are expected in these bands although they are hardly present in the observational data. The kinematical effects connected with the cloud motion affect those features but do not remove them. The level of the primary emission required to model the mean quasar spectrum is too low to reproduce the equivalent width of the iron K$_{\alpha}$ line correctly but more detailed computations may resolve this problem.