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arXiv 0810.2543astro-ph
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用Suzaku和XMM-Newton观测探测NGC4258的吸积盘和中心引擎结构

Probing the accretion disk and central engine structure of NGC4258 with Suzaku and XMM-Newton observations

Christopher S. Reynolds, Michael A. Nowak, Sera Markoff, Jack Tueller, Joern Wilms, Andrew J. Young

摘要:

利用朱雀星、XMM-牛顿和Swift/BAT巡天的数据,对NGC 4258低光度活动星系核(AGN)进行了X射线研究。我们发现,由冷气体的X射线再加工的签名是非常弱的光谱中的这个Seyfert-2星系的弱,窄的冷铁的荧光-Kalpha发射线是强大的朱雀和XMM-牛顿光谱检测,但在一个水平远低于大多数其他Seyfert-2星系。我们的结论是,这个活动星系核的环核环境是非常“干净”的,缺乏康普顿厚的模糊环面的统一塞弗特计划。从狭窄的铁线,连同朱雀和XMM-牛顿观测之间的线通量变化的证据,我们约束线发射区域之间的$3\times 10^3r_g$和$4\times 10^4r_g$从黑洞。我们表明,所观察到的性质的铁线可以解释,如果线起源于表面层的翘曲吸积盘。特别是,我们对来自失调中心黑洞的Lens-Thirring岁差扭曲的圆盘的预期铁线进行了显式计算。最后,朱雀号的数据揭示了在50千秒的时间尺度上存在2- 10千电子伏的大振幅变率以及在5- 10千秒的时间尺度上存在较小振幅的耀斑的明确证据。如果与吸积盘过程有关,这种快速的变化需要在吸积盘的最内部区域($r\approx 10r_g$或更小)的起源。

英文摘要:

[abridged] We present an X-ray study of the low-luminosity active galactic nucleus (AGN) in NGC4258 using data from Suzaku, XMM-Newton, and the Swift/BAT survey. We find that signatures of X-ray reprocessing by cold gas are very weak in the spectrum of this Seyfert-2 galaxy; a weak, narrow fluorescent-Kalpha emission line of cold iron is robustly detected in both the Suzaku and XMM-Newton spectra but at a level much below that of most other Seyfert-2 galaxies. We conclude that the circumnuclear environment of this AGN is very "clean" and lacks the Compton-thick obscuring torus of unified Seyfert schemes. From the narrowness of the iron line, together with evidence for line flux variability between the Suzaku and XMM-Newton observations, we constrain the line emitting region to be between $3\times 10^3r_g$ and $4\times 10^4r_g$ from the black hole. We show that the observed properties of the iron line can be explained if the line originates from the surface layers of a warped accretion disk. In particular, we present explicit calculations of the expected iron line from a disk warped by Lens-Thirring precession from a misaligned central black hole. Finally, the Suzaku data reveal clear evidence for large amplitude 2-10keV variability on timescales of 50ksec as well as smaller amplitude flares on timescales as short as 5-10ksec. If associated with accretion disk processes, such rapid variability requires an origin in the innermost regions of the disk ($r\approx 10r_g$ or less).

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