Twelve years of X-ray and optical variability in the Seyfert galaxy NGC 4051 X-ray/optical variability in NGC 4051
Twelve years of X-ray and optical variability in the Seyfert galaxy NGC 4051 X-ray/optical variability in NGC 4051
复制标题
Seyfert 星系 NGC 4051 十二年的 X 射线和光学变率 NGC 4051 的 X 射线/光学变率
DOI：
10.1111/j.1365-2966.2009.16146.x
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发表时间：
2010
影响因子：
4.8
通讯作者：
Breedt E
中科院分区：
文献类型：
--
作者：
Breedt E
我们讨论了窄线Seyfert 1星系NGC4051光学变化的起源，并给出了用12年多的X射线和光学光曲线进行互相关研究的结果。辐射在所有波段都是高度可变的，即使在对落入测光孔径内的污染的宿主星系通量进行校正后，光学变化的幅度也比X射线的幅度小。光功率谱符合一个完整的幂定律模型，斜率α=1.4+0.6−0.2，在所探测的所有时间尺度上，它的变率比2-10keV的X射线要小。我们发现，在X射线后0.3d的光延迟为1.2x1.0−0.3d时，光曲线是显著相关的。这一时间尺度与到达吸积盘光学发射区的光传播时间一致，表明光学变化是由X射线再处理驱动的。然而，我们证明了一个由扁平吸积盘再处理产生的光学变化的模型不能解释所有的光学变化。在光延迟为39+2.7−8.4d时，互相关函数也有第二个显著峰值。这种滞后与尘埃升华半径是一致的，这表明有相当数量的光通量来自尘埃环。我们从X射线的再处理和尘埃对光学光的反射两个方面讨论了附加光通量的来源。
We discuss the origin of the optical variations in the narrow-line Seyfert 1 galaxy NGC 4051 and present the results of a cross-correlation study using X-ray and optical light curves spanning more than 12 years. The emission is highly variable in all wavebands, and the amplitude of the optical variations is found to be smaller than that of the X-rays, even after correcting for the contaminating host galaxy flux falling inside the photometric aperture. The optical power spectrum is best described by an unbroken power-law model with slope α= 1.4+0.6−0.2and displays lower variability power than the 2–10 keV X-rays on all time-scales probed. We find the light curves to be significantly correlated at an optical delay of 1.2+1.0−0.3d behind the X-rays. This time-scale is consistent with the light traveltime to the optical emitting region of the accretion disc, suggesting that the optical variations are driven by X-ray reprocessing. We show, however, that a model whereby the optical variations arise from reprocessing by a flat accretion disc cannot account for all the optical variability. There is also a second significant peak in the cross-correlation function, at an optical delay of 39+2.7−8.4d. The lag is consistent with the dust sublimation radius in this source, suggesting that there is a measurable amount of optical flux coming from the dust torus. We discuss the origin of the additional optical flux in terms of reprocessing of X-rays and reflection of optical light by the dust.