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arXiv 1204.0946astro-ph.HEastro-ph.CO
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NGC 3147的朱雀X射线谱。关于最佳“真正”塞弗特2星系候选者的进一步见解

The Suzaku X-ray spectrum of NGC 3147. Further insights on the best "true" Seyfert 2 galaxy candidate

G. Matt, S. Bianchi, M. Guainazzi, X. Barcons, F. Panessa

摘要:

NGC 3147是迄今为止最令人信服的“真正”塞弗特2星系的例子,也就是说,它是一个真正缺乏宽线区的星系源。我们获得了朱雀观测的双重目的,以更详细地研究铁线复合物,并检查康普顿厚假设缺乏观察到的光学宽线。详细分析了该源的朱雀XIS和HXD/PIN谱。该线复合物由至少两条未分辨的线组成,一条在约6.45 keV,另一条在约7 keV,最有可能与Fe XVII/XIX(前者)和Fe XXVI(后者)相鉴别。高电离线可以起源于光电离物质或光学薄的热等离子体。在后一种情况下,意味着异常高的温度。在光电离模型的情况下,大的等效宽度可以通过极端的铁过剩或假设源是康普顿厚度来解释。然而,在康普顿厚假设中,高于2 keV的辐射主要是由于高度电离的反射层,与通常在康普顿厚的塞弗特2s中发现的相反,在那里,低电离物质的反射占主导地位。此外,XMM-牛顿和朱雀观测之间的源通量不同,相隔3.5年,证实了以前的发现,并表明发射区域的大小必须小于秒差距。硬X射线谱也不能确定康普顿厚度假说。权衡各种论点,NGC 3147的“真正”塞弗特2性质似乎仍然是最有可能的解释,即使“高度电离的反射层”康普顿厚度假设目前还不能被正式拒绝。

英文摘要:

NGC 3147 is so far the most convincing case of a "true" Seyfert 2 galaxy, i.e. a source genuinely lacking the Broad Line Regions. We obtained a Suzaku observation with the double aim to study in more detail the iron line complex, and to check the Compton-thick hypothesis for the lack of observed optical broad lines. The Suzaku XIS and HXD/PIN spectra of the source were analysed in detail. The line complex is composed of at least two unresolved lines, one at about 6.45 keV and the other one at about 7 keV, most likely identified with Fe XVII/XIX, the former, and Fe XXVI, the latter. The high-ionization line can originate either in a photoionized matter or in an optically thin thermal plasma. In the latter case, an unusually high temperature is implied. In the photoionized model case, the large equivalent width can be explained either by an extreme iron overabundance or by assuming that the source is Compton-thick. In the Compton-thick hypothesis, however, the emission above 2 keV is mostly due to a highly ionized reflector, contrary to what is usually found in Compton-thick Seyfert 2s, where reflection from low ionized matter dominates. Moreover, the source flux varied between the XMM-Newton and the Suzaku observations, taken 3.5 years apart, confirming previous findings and indicating that the size of the emitting region must be smaller than a parsec. The hard X-ray spectrum is also inconclusive on the Compton-thick hypothesis. Weighting the various arguments, a "true" Seyfert 2 nature of NGC 3147 seems to be still the most likely explanation, even if the "highly ionized reflector" Compton-thick hypothesis cannot at present be formally rejected.

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