Active Galactic Nuclei
Active Galactic Nuclei
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DOI：
10.1051/0004-6361:20053730
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发表时间：
2005-10
影响因子：
6.5
通讯作者：
Xiao-Bo Dong;L. C. Ho;Jianguo Wang;Ting-gui Wang;Huiyuan Wang;X. Fan;Hongyan Zhou
中科院分区：
文献类型：
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作者：
Xiao-Bo Dong;L. C. Ho;Jianguo Wang;Ting-gui Wang;Huiyuan Wang;X. Fan;Hongyan Zhou
活动星系核的2-10keV连续谱可以用一个单一的幂定律很好地描述，通常被归因于热压缩介质，如吸积盘上方的日冕。在较小的能量下，连续谱相对于这一幂定律的外推表现出过剩，称为“软X射线过剩”。到目前为止，这要么归因于硬X射线源被吸积盘反射，要么归因于另一种压缩介质的存在。Gierlinski&Done(2004)提出的另一种解决方案是，单一的幂定律正确地表示了软X射线和硬X射线的发射，而软X射线过剩是由于相对论风吸收一次幂定律而产生的伪影。我们研究了反射与吸收模型的优点和缺点。我们认为，在吸收假设中，吸收介质应该处于总压平衡，以限制光谱分布，否则与观测结果相比，光谱分布在时间上和从一个物体到另一个物体的变化太大。我们得出结论，在0.3-10keV范围内，某些X射线谱，特别是那些具有较强软X射线过剩的X射线谱，可以用吸收来模拟。然而，由于缺乏一个完整的模型网格和10keV以上的良好数据，我们目前不能得出结论，所有物体都可以容纳这样的模型。这些吸收模型要么意味着具有爱丁顿值量级(甚至更大)质量速率的强相对论外流，要么意味着准球形非均匀吸积流。只有微弱的过剩才能用反射来模拟，除非原始连续体不能被直接看到。最后，被温和的相对论风吸收的反射模型可能是解决这个问题的最佳方案。
The 2-10 keV continuum of AGN is well represented by a single power law, generally attributed to a hot comptonizing medium, such as a corona above the accretion disk. At smaller energies the continuum displays an excess with respect to the extrapolation of this power law, called the "soft X-ray excess". Until now it was attributed, either to reflection of the hard X-ray source by the accretion disk, or to the presence of an additional comptonizing medium. An alternative solution proposed by Gierlinski & Done (2004) is that a single power law represents correctly both the soft and the hard X-ray emission, and the soft X-ray excess is an artefact due to the absorption of the primary power law by a relativistic wind. We examine the advantages and drawbacks of the reflection versus absorption models. We argue that in the absorption hypothesis, the absorbing medium should be in total pressure equilibrium, to constrain the spectral distribution which otherwise would be too strongly variable in time and from one object to the other, as compared to observations. We conclude that some X-ray spectra, in particular those with strong soft X-ray excesses, can be modelled by absorption in the 0.3-10 keV range. However, due to the lack of a complete grid of models and good data extending above 10 keV, we are not able to conclude presently that all objects can be accommodated with such models. These absorption models imply either strong relativistic outflowing winds with mass rates of the order of the Eddington value (or even larger), or quasi-spherical inhomogeneous accretion flows. Only weak excesses can be modelled by reflection, unless the primary continuum is not directly seen. Finally, a reflection model absorbed by a modest relativistic wind could be the best solution to the problem.