X射线的星际吸收与散射

Accurate estimates of the absorption and scattering of X-rays by interstellar gas and dust are of crucial importance for the analysis and interpretation of almost all astronomical soft X-ray observations. While the X-ray absorption data computed by Wilms et al. (2000) have been most extensively used by the X-ray community, their results were computed based on the assumption of a reduced interstellar abundance (i.e., they assumed that the interstellar abundance is just ~70% of solar). With such a subsolar interstellar abundance, there will be a shortage of raw material to form the dust to account for the observed interstellar extinction in the ultraviolet, optical and near infrared. Also, Wilms et al. (2000) used the self-shielding approximation to estimate the X-ray absorption of dust which ignores scattering. Therefore, the X-ray absorption data of Wilms et al. (2000) could have been substantially underestimated by a factor of more than 4. We propose to update the interstellar X-ray absorption and scattering by making use of updated atomic cross sections, updated interstellar abundances, incorporating the interstellar abundances, reliable dust model and realistic X-ray dust physics.

对于几乎所有软X射线天文观测的分析和解释，精确扣除星际气体和尘埃对X射线的吸收和散射都是至关重要的。当前广泛采用的X射线星际吸收数据是基于Wilms等人近20年前的模型。该模型假定星际元素丰度仅为太阳的70%。然而，这样的“亚太阳”丰度会使得形成星际尘埃的“原材料”不够，因而不足以解释紫外-光学-近红外波段的星际消光。另外，Wilms 等人忽略了星际尘埃对X射线的散射，仅考虑了吸收。因此，Wilms模型给出的X射线星际吸收实际上被低估超过4倍。我们拟采用最新的原子分子X射线吸收截面，最新的星际元素丰度，合理的星际尘埃模型，以及更为准确的X射线尘埃物理，来精确计算X射线的星际吸收和散射。

对于几乎所有软X射线天文观测的分析和解释，精确扣除星际气体和尘埃对X射线的吸收和散射都是至关重要的。当前广泛采用的X射线星际吸收数据是基于Wilms等人近20年前的模型，但该模型具有两个显著的缺陷：(1)元素丰度值低于观测上紫外-光学-近红外波段的消光曲线的所需元素含量的要求；(2)忽略了星际尘埃对X射线的散射作用，因此Wilms模型给定的X射线星际消光被低估。我们采用了最新的原子分子X射线吸收截面，最新的星际元素丰度，合理的星际尘埃模型，以及更为准确的X射线尘埃物理，精确计算了X射线的星际吸收和散射。研究结果表明，以“原太阳+银河系元素增丰”情况下的元素丰度为星际元素丰度参考值，能够最佳拟合观测上银河系紫外-光学-近红外波段的消光曲线，由此得到的星际X射线消光截面为近30年来最为精确数据，尤其是将为我国在研的eXTP等X射线天文卫星的科学研究提供准确的X射线能谱星际消光改正模型。基于本项目，3年内发表SCI/EI论文6篇。