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arXiv 1202.2797astro-ph.HE
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Seyfert 1星系MCG-6-30-15的可变部分覆盖模型

A Variable Partial Covering Model for the Seyfert 1 Galaxy MCG-6-30-15

Takehiro Miyakawa, Ken Ebisawa, Hajime Inoue

摘要:

我们为塞弗特1星系MCG-6-30-15提出了一个简单的光谱模型,它可以通过改变部分覆盖分数来解释1 - 40 keV光谱变化的大部分,类似于Miller等人提出的模型。我们的光谱模型由三个连续分量组成:(1)直接幂律分量,(2)被轻度电离的介入物质严重吸收的幂律分量,(3)远离黑洞的冷盘反射分量,具有中等立体角(Ω/2π \approx 0.3),伴随着窄的荧光铁线。前两个分量受周围高电离薄吸收体的影响,其N_H \approx为10^{23.4}cm-2,对数吸收系数\approx为3.4。第二部分中的重吸收体分裂成许多云,每个云由具有不同电离状态和柱密度的辐射区、主体(N_H \approx 10^24.2 cm-2,log H2O \approx 1.6)、包层(N_H \approx 10^22.1 cm-2,log H2O \approx 1.9)和可能完全不透明的核心组成。电离吸收体的这些参数以及X射线源的固有光谱形状完全不变。中央的X射线源是适度延伸的,它的光度变化不大。观测到的通量和光谱变化主要是由中心源的几何部分覆盖率从0(未覆盖)到\sim 0.63的视线中的电离云的干预的变化来解释。重吸收组分的电离铁K边缘解释了大多数看似宽的线状特征,这是MCG-6-30-15的一个众所周知的光谱特征。直接分量和吸收分量反相关,相互抵消它们的变化,使得分数光谱变化在铁能带处最小,从而解释了MCG-6-30-15的另一个观测特征。

英文摘要:

We propose a simple spectral model for the Seyfert 1 Galaxy MCG-6-30-15 that can explain most of the 1 - 40 keV spectral variation by change of the partial covering fraction, similar to the one proposed by Miller et al. (2008). Our spectral model is composed of three continuum components; (1) a direct power-law component, (2) a heavily absorbed power-law component by mildly ionized intervening matter, and (3) a cold disk reflection component far from the black hole with moderate solid-angle (Ω/2π \approx 0.3) accompanying a narrow fluorescent iron line. The first two components are affected by the surrounding highly ionized thin absorber with N_H \approx 10^{23.4}cm-2 and log ξ \approx 3.4. The heavy absorber in the second component is fragmented into many clouds, each of which is composed of radial zones with different ionization states and column densities, the main body (N_H \approx 10^24.2cm-2, log ξ \approx 1.6), the envelope (N_H \approx 10^22.1cm-2, log ξ \approx 1.9) and presumably a completely opaque core. These parameters of the ionized absorbers, as well as the intrinsic spectral shape of the X-ray source, are unchanged at all. The central X-ray source is moderately extended, and its luminosity is not significantly variable. The observed flux and spectral variations are mostly explained by variation of the geometrical partial covering fraction of the central source from 0 (uncovered) to \sim0.63 by the intervening ionized clouds in the line of sight. The ionized iron K-edge of the heavily absorbed component explains most of the seemingly broad line-like feature, a well-known spectral characteristic of MCG-6-30-15. The direct component and the absorbed component anti-correlate, cancelling their variations each other, so that the fractional spectral variation becomes the minimum at the iron energy band; another observational characteristic of MCG-6-30-15 is thus explained.

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