[论文解读] Weighing Super-Massive Black Holes with Narrow Fe K$\alpha$ Line

Peng Jiang, Junxian Wang+1 more|arXiv (Cornell University)|Mar 10, 2011

Astrophysical Phenomena and Observations被引用 7

一句话总结

本文提出，塞弗特1型星系中窄的Fe Kα线起源于内环面，利用红外时延测量其半径；然而，观测到的线宽比在各向同性辐射下预期的宽2.6⁺⁰.⁹₋₀.⁴倍，表明可能存在厚盘几何结构或其它区域的污染，且由于样本量小和不确定性大，该方法与既有的黑洞质量测量结果之间的统计相关性较弱。

ABSTRACT

It has been suggested that the narrow cores of the Fe K$\alpha$ emission lines in Active Galactic Nuclei (AGNs) are likely produced in the torus, the inner radius of which can be measured by observing the lag time between the $V$ and $K$ band flux variations. In this paper we compare the virial products of the infrared time lags and the narrow Fe K$\alpha$ widths for 10 type 1 AGNs with the black hole masses from other techniques. We find the narrow Fe K$\alpha$ line width is in average 2.6$^{+0.9}_{-0.4}$ times broader than expected assuming an isotropic velocity distribution of the torus at the distance measured by the infrared lags. We propose the thick disk model of the torus could explain the observed larger line width. Another possibility is the contamination by emission from the broad line region or the outer accretion disk. Alternatively, the narrow iron line might originate from the inner most part of the obscuring torus within the sublimation radius, while the infrared emission from outer cooler part. We note the correlation between the black hole masses based on this new technique and those based on other known techniques is statistically insignificant. We argue that this could be attributed to the small sample size and the very large uncertainties in the measurements of iron K line widths. The next generation of X-ray observatories could help verify the origin of the narrow iron K$\alpha$ line and the reliability of this new technique.

研究动机与目标

• 检验活动星系核中的窄Fe Kα线是否可作为测量黑洞质量的可靠工具。
• 通过将线宽与由红外时延推导出的环面内半径进行比较，探究窄Fe K Kα线的起源。
• 评估由Fe Kα线宽推导出的黑洞质量与其它成熟技术所得结果的一致性。
• 评估不确定性和样本大小对这一新质量估算方法可靠性的影响。

提出的方法

• 通过测量V波段与K波段流量变化之间的时延，估算10个塞弗特1型星系中环面的内半径。
• 测量X射线谱中窄Fe Kα发射线的宽度，以推断发射物质的速度弥散度。
• 将推导出的半径与线宽的维里积与其它方法所得的黑洞质量进行比较。
• 评估在时延推导出的半径处，Fe Kα线宽是否与各向同性速度分布一致。
• 测试厚盘环面或来自宽线区或外吸积盘污染的替代模型。
• 评估由Fe Kα线与其它技术所得质量之间相关性的统计显著性。

实验结果

研究问题

• RQ1 活动星系核中的窄Fe Kα线是否产生于红外时延测得半径处的环面？
• RQ2 为何在时延测得半径处，观测到的Fe Kα线宽比各向同性辐射下的预期更宽？
• RQ3 环面的厚盘模型能否解释观测到的线宽展宽？
• RQ4 Fe Kα线在多大程度上受到宽线区或外吸积盘发射的污染？
• RQ5 与成熟技术相比，Fe Kα线宽方法在测量黑洞质量方面有多可靠？

主要发现

• 若环面内发射物质在红外时延测得的半径处具有各向同性速度分布，窄Fe Kα线宽平均比预期宽2.6⁺⁰.⁹₋₀.⁴倍。
• 观测到的线宽展宽可能由环面的厚盘几何结构解释，该结构自然导致速度分布各向异性。
• 其他可能解释包括来自宽线区或外吸积盘的发射污染。
• 由Fe Kα线宽与其它技术所得黑洞质量之间的相关性在统计上不显著，可能由于样本量小和测量不确定性大。
• 未来的X射电望远镜有望提高线宽测量的精度，并有助于验证窄Fe Kα线的起源。