arXiv 1405.26452014-05-22astro-ph.GAastro-ph.COastro-ph.HE

活动星系核中的Fe K窄$α$线和分子环--IR/X射线观测

The narrow Fe K$α$ line and the molecular torus in active galactic nuclei - an IR/X-ray view

Claudio Ricci, Yoshihiro Ueda, Kohei Ichikawa, Stephane Paltani, Rozenn Boissay, Poshak Gandhi, Marko Stalevski, Hisamitsu Awaki

备注：: A&A in press, 15 pages, 5 Figures, 3 tables - Few references updated
发表信息：: A&A 567, A142 (2014)
DOI：: 10.1051/0004-6361/201322701

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摘要：

铁K $α$的窄组分在活动星系核（AGN）的X射线谱中几乎是普遍存在的特征，并且被认为起源于中性物质，可能位于分子环中。这将意味着铁K $α$等效宽度（EW）和环面的物理性质之间的紧密联系。在最近的一项工作中，我们已经表明，环面的覆盖因子随着光度的减少，正如光度依赖的统一模型所预期的那样，将能够解释Fe K $α$ EW随着光度的减少（即，X射线鲍德温效应）。活动星系核中红外光谱研究的最新进展使得人们可以利用星团环面模型来推导活动星系核的重要参数，如覆盖因子（$f_{\rm\,obs}$）和赤道柱密度（$N_{\rm\,H}^{\rm\,T}$）。利用对24个Ⅰ型活动星系核样品的XMM Newton/EPIC观测，研究了最近MIR工作获得的环面物理参数与Fe K $α$线性质之间的关系.我们采取的倾斜角，光子指数，赤道柱密度，半开角的环面考虑使用物理环面模型的X射线再处理辐射的Fe K $α$ EW的值。我们发现，铁K $α$ EW和$f_{\rm\,obs}$之间的关系显示出与预期值一致的斜率，尽管具有较低的统计显著性。当比较Fe K $α$ EW和$N_{\rm\,H}^{\rm\,T}$时，也发现了与理论预测一致的趋势。我们的工作似乎证实，大量的窄Fe K $α$线是由负责MIR发射的相同材料产生的。

英文摘要：

The narrow component of the iron K$α$ is an almost ubiquitous feature in the X-ray spectra of active galactic nuclei (AGN) and is believed to originate in neutral material, possibly located in the molecular torus. This would imply a tight connection between the Fe K$α$ equivalent width (EW) and the physical properties of the torus. In a recent work we have shown that the decrease of the covering factor of the torus with the luminosity, as expected by luminosity-dependent unification models, would be able to explain the decrease of Fe K$α$ EW with the luminosity (i.e., the X-ray Baldwin effect). Recent developments in the study of the mid-IR (MIR) spectrum of AGN allow important parameters of the torus to be deduced, such as its covering factor ($f_{\rm\,obs}$) and equatorial column density ($N_{\rm\,H}^{\rm\,T}$), by applying clumpy torus models. Using XMM-Newton/EPIC observations of a sample of 24 type-I AGN, we investigate the relation between the physical parameters of the torus obtained by recent MIR works and the properties of the Fe K$α$ line. We correct the values of the Fe K$α$ EW by taking the inclination angle, the photon index, the equatorial column density, and half-opening angle of the torus into account using a physical torus model of X-ray reprocessed radiation. We find that the relation between Fe K$α$ EW and $f_{\rm\,obs}$ shows a slope that is consistent with the expected value, albeit with a low statistical significance. A trend that is consistent with the theoretical prediction is also found when comparing the Fe K$α$ EW to $N_{\rm\,H}^{\rm\,T}$. Our work seems to confirm that the bulk of the narrow Fe K$α$ line is produced by the same material responsible for the MIR emission.

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