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arXiv 0905.1266astro-ph.HE
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低光度活动星系核的可变性:用Swift同时观测X射线/UV

Variability of low-luminosity AGNs: a simultaneous X-ray/UV look with Swift

P. Romano, E. Pian, D. Maoz, A. Cucchiara, C. Pagani, V. La Parola

摘要:

我们提出的调查结果的X射线和紫外线性质的四个LINER观察Swift,旨在构建良好的S/N和严格同步的UV-X射线的SEDs。在目前的范例中,LINER发射主要是由几何厚,辐射效率低的辐射流(RIAF),而不是辐射效率高,几何薄的吸积盘被认为是动力更高的光度AGN(塞弗茨和类星体)。然而,最近的一些研究发现LINER和更明亮的AGN的SED之间的相似性大于差异,这表明LINER由更高亮度AGN中活跃的相同机制提供动力。我们的新观察使我们能够测试这个想法。特别地,XRT提供对X射线发射的长时间和灵敏的监测。我们在M81和NGC 3998中首次发现了显著的变异。M81和NGC 3998的最大振幅变化在几小时的时间尺度上都达到30%。NGC 3998在9天的时间尺度上表现出相同幅度的变化。M81在2年内变化很大,在6个月内最大变化为2倍。在我们的两个源中,特别是在NGC 3998中检测到的X射线可变性,对将其动力机制解释为低效吸积流提出了质疑,因为该模型的特征之一是缺乏可变性。NGC 3998与低功率活动星系核的鉴别似乎更可行。

英文摘要:

We present the results of an investigation of the X-ray and UV properties of four LINERs observed with Swift, aimed at constructing good S/N and strictly simultaneous UV-X-ray SEDs. In the current paradigm, LINER emission is dominated by geometrically thick, radiatively inefficient radiation flows (RIAFs) as opposed to radiatively efficient, geometrically thin accretion disks thought to power higher luminosity AGNs (Seyferts and QSOs). However, some recent studies have found more similarities than differences between the SEDs of LINERs and those of more luminous AGNs, suggesting that LINERs are powered by the same mechanisms active in higher luminosity AGNs. Our new observations allow us to test this idea. In particular, XRT affords long and sensitive monitoring of the X-ray emission. We detect significant variability in M81 and, for the first time, in NGC 3998. The maximum amplitude variations over time scales of some hours are 30% in both M81 and NGC 3998. NGC 3998 exhibits a variation of the same amplitude on a time scale of 9 days. M81 varies significantly over 2 years, with a maximum change of a factor 2 in 6 months. The X-ray variability detected in 2 of our sources, and in particular in NGC 3998, puts into question the interpretation of their powering mechanism as an inefficient accretion flow, because one of the characteristics of this model is the lack of variability. The identification of NGC 3998 with a low power AGN appears more viable.

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