活动核H0557-385中玩捉迷藏的朦胧云
Obscuring clouds playing hide-and-seek in the Active Nucleus H0557-385
摘要：
本文报道了2006年获得的两个XMM-牛顿观测的塞弗特1星系H 0557 -385，这表明源处于历史低通量状态，比2002年的XMM-牛顿观测低10倍以上。低通量谱呈现出与康普顿反射连续谱相关联的强Fe K α线。需要一个额外的谱线约6.6 keV，以适应从Fe XXV的Ka发射。低于6 keV的光谱曲率意味着被柱密度为8*10^{23}cm^{-2}的中性气体遮蔽，部分覆盖了主发射，这仍然贡献了软X射线发射的百分之几。电离物质在视线上的吸收需要适合低于1 keV的深槽。两种光谱状态的比较表明，通量转换是完全归因于干预线的视线云与高柱密度。
英文摘要：
This paper reports on two XMM-Newton observations of the Seyfert 1 Galaxy H0557-385 obtained in 2006, which show the source at an historical low flux state, more than a factor of 10 lower than a previous XMM-Newton look in 2002. The low flux spectrum presents a strong Fe Kalpha line associated to a Compton reflection continuum. An additional spectral line around 6.6 keV is required to fit Kalpha emission from Fe XXV. The spectral curvature below 6 keV implies obscuration by neutral gas with a column density of 8*10^{23}cm^{-2} partially covering the primary emission, which still contributes for a few percent of the soft X-ray emission. Absorption by ionised material on the line of sight is required to fit the deep trough below 1 keV. The comparison of the two spectral states shows that the flux transition is to be ascribed entirely to intervening line-of-sight clouds with high column density.
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