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arXiv 0901.2215astro-ph.GA
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IGR J16351-5806:另一个接近康普顿厚度的AGN

IGR J16351-5806: another close by Compton-thick AGN

A. Malizia, L. Bassani, F. Panessa, A. De Rosa, A. J. Bird

摘要:

IGR J16351-5806与塞弗特2星系ESO 137-G34有关,在第三次INTEGRAL/IBIS巡天中首次被报道为高能发射体。Malizia等人(2007)使用一种基于X射线柱密度测量与软度比的新诊断工具,将该源确定为候选的康普顿厚活动星系核。本文分析了IGR J16351-5806的XMM-Newton和INTEGRAL组合数据,研究了它的宽带谱,探讨了它的康普顿厚性质。在6.4keV(EW > 1 keV)附近的显著K_α荧光线与2-10 keV的平坦光谱一起立即指向高度遮蔽的源。整个光谱可以解释为透射情况,其中一些高能辐射能够穿透厚吸收层,但使用纯反射光谱也可以获得良好的拟合。另一种可能性是复合吸收,其中在IGR J16351-5806中存在两层吸收物质,每层吸收物质部分地覆盖中心核。从统计学的观点来看,这三种假设都是相容的,并提供了合理的活动星系核光谱参数;更重要的是,它们都指向一个吸收柱大于1.5 x 10^24 cm^-2的源,即康普顿厚度的活动星系核。由于这种严重的遮蔽,一些额外的成分,否则将被隐藏,能够出现在低能量和可以研究。通过对IGR J16351-5806的康普顿厚性质提供强有力的证据,我们间接地证实了Malizia等人诊断图的有效性。

英文摘要:

IGR J16351-5806 has been associated with the Seyfert 2 galaxy ESO 137-G34, having been first reported as a high energy emitter in the third INTEGRAL/IBIS survey. Using a new diagnostic tool based on X-ray column density measurements vs softness ratios, Malizia et al. (2007) identified this source as a candidate Compton thick AGN. In the present work we have analysed combined XMM-Newton and INTEGRAL data of IGR J16351-5806 in order to study its broad band spectrum and investigate its Compton thick nature. The prominent K_alpha fluorescence line around 6.4 keV (EW > 1 keV) together with a flat 2-10 keV spectrum immediately point to a highly obscured source. The overall spectrum can be interpreted in terms of a transmission scenario where some of the high energy radiation is able to penetrate through the thick absorption but a good fit is also obtained using a pure reflection spectrum. An alternative possibility is that of a complex absorption, where two layers of absorbing matter each partially covering the central nucleus are present in IGR J16351-5806. All three scenarios are compatible from a statistical viewpoint and provide reasonable AGN spectral parameters; more importantly all point to a source with an absorbing column greater than 1.5 x 10^24 cm^-2, i.e. to a Compton thick AGN. Because of this heavy obscuration, some extra components which would otherwise be hidden are able to emerge at low energies and can be studied. By providing strong evidence for the Compton thick nature of IGR J16351-5806, we indirectly confirm the validity of the Malizia et al. diagnostic diagram.

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