Can the relativistic light-bending model explain X-ray spectral variations of Seyfert galaxies?
Can the relativistic light-bending model explain X-ray spectral variations of Seyfert galaxies?
复制标题
相对论光弯曲模型能否解释 Seyfert 星系的 X 射线光谱变化？
DOI：
10.1093/pasj/psy032
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发表时间：
2018
影响因子：
2.3
通讯作者：
Tsujimoto Masahiro
中科院分区：
文献类型：
--
作者：
Mizumoto Misaki;Moriyama Kotaro;Ebisawa Ken;Mineshige Shin;Kawanaka Norita;Tsujimoto Masahiro
许多塞弗特星系的X射线能谱都具有铁-钾宽发射线的特征。观测到的谱线有三个明显的特征：（1）谱线轮廓是倾斜的，并显示出明显的低能尾;（2）Fe-K带的变化率很低，这使谱线的均方根（rms）有一个宽而深的凹陷;（3）该带的光子相对于相邻能带的光子有几个Rg/c的时间滞后，其中Rg/c是引力半径。提出“相对论性光弯曲模型”来解释这些观察到的特征，其中极端克尔黑洞上方的紧凑X射线源（“灯柱”）照亮了吸积盘的最内部区域。在本文中，我们批判性地研究相对论性光弯曲模型计算的均方根谱和滞后功能，使用射线跟踪技术，当一个灯柱上的黑洞自旋轴垂直移动。因此，我们发现，所观察到的深均方根倾角要求铁是非常过剩的（1000太阳能），而所观察到的滞后幅度与正常的铁丰度是一致的。此外，在高通量状态的滞后消失需要一个源的高度高达1040 Rg，这与相对论宽的发射线的功能。我们的模拟与混响特征随着较大的源高度移动到较低频率的数据一致;然而，如果这种情况是正确的，则模拟预测在低频处检测到明显的Fe-K滞后，这在数据中不受约束。因此，我们得出结论，相对论性光弯曲模型可能无法解释Seyfert星系的特征Fe-K光谱变化。
Many Seyfert galaxies are known to exhibit Fe-K broad emission line features in their X-ray energy spectra. The observed lines have three distinct features: (1) the line profiles are skewed and show significant low-energy tails, (2) the Fe-K band has low variability, which produces a broad and deep dip in the root-mean-square (rms) spectra, and (3) photons in this band have time lags behind those in the adjacent energy bands with amplitudes of severalRg/c, whereRgis the gravitational radius. The “relativistic light-bending model” is proposed to explain these observed features, where a compact X-ray source (“lamp post”) above an extreme Kerr black hole illuminates the innermost area of the accretion disc. In this paper, we critically examine the relativistic light-bending model by computing the rms spectra and the lag features using a ray-tracing technique, when a lamp post moves vertically on the black hole spin axis. As a result, we found that the observed deep rms dip requires that the iron is extremely overabundant (≳10 solar), whereas the observed lag amplitude is consistent with the normal iron abundance. Furthermore, disappearance of the lag in the high-flux state requires a source height as high as ∼40Rg, which contradicts the relativistically broad emission line feature. Our simulations agree with the data that the reverberation feature moves to lower frequencies with larger source height; however, if this scenario is correct, the simulations predict the detection of a clear Fe-K lag at low frequencies, which is not constrained in the data. Therefore, we conclude that the relativistic light-bending model may not explain the characteristic Fe-K spectral variations in Seyfert galaxies.