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arXiv 1408.2341astro-ph.HE
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利用光学混响映射抑制有源星系中黑洞自旋的新方法

A New Approach to Constrain Black Hole Spins in Active Galaxies Using Optical Reverberation Mapping

Jian-Min Wang, Pu Du, Yan-Rong Li, Luis C. Ho, Chen Hu, Jin-Ming Bai

摘要:

通过对H β宽谱线的反射测绘,研究了约50个活动星系核的宽谱线区(BLR)的大小与光学光度之间的关系。R_blr-L关系源于简单的光电离考虑。利用广义相对论模型的光学厚,几何薄吸积盘,我们表明,电离光度共同依赖于黑洞质量,吸积率,和自旋。电离光度和光学光度之间的非单调关系导致了BLR尺寸和光学光度之间的复杂关系。我们发现,混响滞后的H β的变化连续非常敏感地依赖于黑洞自旋。对于逆行自旋,盘是如此的冷,以至于BLR中的电离光子不足,导致氢电离前沿随着光学亮度的增加而收缩,从而缩短了Hbeta滞后。这种效应在经历倒吸积的亮类星体中尤为显著,表现为对正则R_blr-L关系的强烈偏离。这可能导致一种方法来估计类星体的黑洞自旋和研究它们的宇宙演化。与此同时,对于当前反射映射的活动星系样本,所观察到的R_blr-L关系的小散射意味着这些源中的大多数具有快速旋转的黑洞。

英文摘要:

A tight relation between the size of the broad-line region (BLR) and optical luminosity has been established in about 50 active galactic nuclei studied through reverberation mapping of the broad Hbeta emission line. The R_blr-L relation arises from simple photoionization considerations. Using a general relativistic model of an optically thick, geometrically thin accretion disk, we show that the ionizing luminosity jointly depends on black hole mass, accretion rate, and spin. The non-monotonic relation between the ionizing and optical luminosity gives rise to a complicated relation between the BLR size and the optical luminosity. We show that the reverberation lag of Hbeta to the varying continuum depends very sensitively to black hole spin. For retrograde spins, the disk is so cold that there is a deficit of ionizing photons in the BLR, resulting in shrinkage of the hydrogen ionization front with increasing optical luminosity, and hence shortened Hbeta lags. This effect is specially striking for luminous quasars undergoing retrograde accretion, manifesting in strong deviations from the canonical R_blr-L relation. This could lead to a method to estimate black hole spins of quasars and to study their cosmic evolution. At the same time, the small scatter of the observed R_blr-L relation for the current sample of reverberation-mapped active galaxies implies that the majority of these sources have rapidly spinning black holes.

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