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arXiv 1202.1291astro-ph.HE
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高吸收AGN的X射线颜色选择

X-ray colour-colour selection for heavily absorbed AGN

Murray Brightman, Kirpal Nandra

摘要:

本文提出了一种从X射线光度数据中鉴别重吸收活动星系核(NH>10^23 cm^-2)的方法。我们这样做,使用一组XMM-牛顿参考光谱的本地星系,我们有准确的NH信息,如所描述的Rehman和Nandra。该技术使用两个静止帧硬度比,这是优化的这项任务,我们指定HR 1(2-4/1-2 keV)和HR 2(4-16/2-4 keV)。选择方法利用的事实,而模糊AGN出现硬HR 2由于吸收的内在源通量低于~4千电子伏,他们出现软HR 1由于过量的发射来自散射源光,热发射,或主机星系发射。这种辐射在低红移的样品中普遍存在。该技术提供了一个非常简单和直接的方法来估计样本中的活动星系核的比例与相对较低的信噪比在X射线波段。我们将这一技术应用于来自钱德拉深场北的中等红移(z~1)活动星系核样本,发现该样本中有61%的NH> 10^23 cm^-2。从我们的分析中得出的一个明确而有力的结论是,在深度调查中,绝大多数源都没有显示出与简单吸收幂律一致的硬度比。复杂光谱的普遍存在反过来表明,简单的硬度比分析将不会产生可靠的遮蔽估计,证明本文中描述的更复杂的颜色-颜色分析。虽然这种方法可以很好地将NH> 10^23 cm^-2的源与NH较低的源分开,但只有X射线光谱学可以通过检测Fe Ka线来识别康普顿厚源。ATHENA的高通量X射线光谱能力将使这成为可能。

英文摘要:

We present a method for the identification of heavily absorbed AGN (NH>10^23 cm^-2) from X-ray photometric data. We do this using a set of XMM-Newton reference spectra of local galaxies for which we have accurate NH information, as described in Brightman & Nandra. The technique uses two rest-frame hardness ratios which are optimised for this task, which we designate HR1 (2-4/1-2 keV) and HR2 (4-16/2-4 keV). The selection method exploits the fact that while obscured AGN appear hard in HR2 due to absorption of the intrinsic source flux below ~4 keV, they appear soft in HR1 due to excess emission originating from scattered source light, thermal emission, or host galaxy emission. Such emission is ubiquitous in low redshift samples. The technique offers a very simple and straight forward way of estimating the fraction of obscured AGN in samples with relatively low signal-to-noise ratio in the X-ray band. We apply this technique to a moderate redshift (z~1) sample of AGN from the Chandra Deep Field North, finding that 61% of this sample has NH> 10^23 cm^-2. A clear and robust conclusion from our analysis, is that in deep surveys the vast majority of sources do not show hardness ratios consistent with a simple absorbed power-law. The ubiquity of complex spectra in turn shows that simple hardness ratio analysis will not yield reliable obscuration estimates, justifying the more complex colour-colour analysis described in this paper. While this method does very well at separating sources with NH> 10^23 cm^-2 from sources with lower NH, only X-ray spectroscopy can identify Compton thick sources, through the detection of the Fe Ka line. This will be made possible with the high throughput X-ray spectral capabilities of ATHENA.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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