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arXiv 1002.2062astro-ph.COastro-ph.HE
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矮塞弗特星系NGC4395的朱雀宽带X射线谱

The Suzaku broadband X-ray spectrum of the dwarf Seyfert galaxy NGC4395

K. Iwasawa, Y. Tanaka, L. C. Gallo

摘要:

我们对矮塞弗特星系NGC 4395进行了朱雀观测,估计其黑洞质量约为10^5 Msun。快速和强大的X射线的变化与均方根幅度约60%,观察到在0.4-10千电子伏波段与XIS相机。光变曲线的形状似乎取决于能量。HXD-PIN探测器在与INTEGRAL IBIS相似的通量水平下检测到高达35 keV的硬X射线发射。当采用简单的吸收模型时,10 keV以下的X射线谱被平均等效氢柱密度为~ 2 e22 cm^-2的部分电离(xi~35)气体强烈吸收。光谱形状也是强可变的,但不是源亮度的简单函数。光谱的变化似乎主要是占连续斜率的变化,但电离吸收体的变化也可能发挥一定的作用。明显平坦的光谱斜率与光子指数为1.4低于10千电子伏,吸收校正后获得的,是轻微不一致的光子指数2推断从14-35千电子伏PIN光谱。如果真实的光谱斜率与硬X射线波段测量的一样陡,那么就会有一个我们无法检测到的额外吸收成分。与INTEGRAL测量相结合,10 keV以上的硬X射线发射在光度方面超过了光发射,并主导了宽带能量输出,除非在不可观测的波段中还没有检测到大量过量的UV盘发射。在6.4 keV处观察到一条弱的Fe K线,平均等效宽度为110 eV,在3天的观测中没有显示出明显的通量变化。

英文摘要:

We present a Suzaku observation of the dwarf Seyfert galaxy NGC4395 with an estimated black hole mass of ~10^5 Msun. Rapid and strong X-ray variability with an rms amplitude of ~60 per cent is observed in the 0.4-10 keV band with the XIS cameras. The shape of the light curve appears to depend on energies. The hard X-ray emission is detected up to 35 keV with the HXD-PIN detector at a similar flux level as observed with the INTEGRAL IBIS. The X-ray spectrum below 10 keV is strongly absorbed by partially ionized (xi~35) gas with a mean equivalent hydrogen column density of ~2e22 cm^-2, when a simple absorption model is applied. The spectral shape is also strongly variable but not a simple function of the source brightness. The spectral variability appears to be accounted for mainly by continuum slope changes, but variability in the ionized absorber may also play some part. The apparently flat spectral slope with photon index of 1.4 below 10 keV, obtained after correcting for absorption, is marginally inconsistent with the photon index of 2 inferred from the 14-35 keV PIN spectrum. If the true spectral slope was as steep as that measured in the hard X-ray band, there would be an extra absorption component, which we are unable to detect. Combined with the INTEGRAL measurements, the hard X-ray emission above 10 keV exceeds the optical emission in terms of luminosity and dominates the broadband energy output, unless a large excess of UV disk emission is yet to be detected in the unobservable band. A weak Fe K line is seen at 6.4 keV with the average equivalent width of 110 eV, which does not show clear flux changes over the 3-day observation.

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