摘要
It has been suggested that the narrow cores of the Fe Ka 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 Ka widths for 10 type 1 AGNs, with the black hole masses from other techniques. We found the narrow Fe Ka 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 may 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 may be from the outer cooler part. We note the correlations between the black hole masses based on this new technique and those based on other known techniques are 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 Ka line and the reliability of this new technique.
It has been suggested that the narrow cores of the Fe Kα emission lines in Active Galactic Nuclei(AGNs) are likely produced in thetorus,the inner radius of which can be measured by observing the lag time between the V and K band-ux variations.In this paper,we compare the virial products of the infrared time lags,and the narrow Fe Kα widths for 10 type 1 AGNs,with the black holemasses from other techniques.We found the narrow Fe Kα line width is in average 2.6-+00..49 times broader than expected,assumingan isotropic velocity distribution of the torus at the distance measured by the infrared lags.We propose the thick disk model of thetorus may explain the observed larger line width.Another possibility is the contamination by emission from the broad line regionor the outer accretion disk.Alternatively,the narrow iron line might originate from the inner most part of the obscuring torus withinthe sublimation radius,while the infrared emission may be from the outer cooler part.We note the correlations between the blackhole masses based on this new technique and those based on other known techniques are statistically insignificant.We argue thatthis could be attributed to the small sample size and the very large uncertainties in the measurements of iron K line widths.The nextgeneration of X-ray observatories could help verify the origin of the narrow iron Kα line and the reliability of this new technique.
基金
supported by the National Natural Science Foundation of China (Grant Nos. 10773010 and 10825312)
support from the "Chuang Xin" Foundation operated by the Graduate School of University of Science and Technology of China
