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arXiv 1102.0775astro-ph.HEgr-qc
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近红外偏振测量作为检验吸积超大质量黑洞性质的工具

Near-infrared polarimetry as a tool for testing properties of accreting super-massive black holes

M. Zamaninasab, A. Eckart, M. Dovciak, V. Karas, R. Schoedel, G. Witzel, N. Sabha, M. Garcia-Marin, D. Kunneriath, K. Muzic, C. Straubmeier, M. Valencia-S, J. A. Zensus

摘要:

几个大质量的黑洞在时间尺度上表现出通量的变化,对应于几个史瓦西半径量级的源大小。我们调查了近红外和X射线偏振测量的潜力,以约束这样的黑洞系统的物理性质,即它们的自旋和倾角。我们已经集中在一个模型中的轨道热点是嵌入在一个吸积盘。一种新的方法,搜索正交极化通道之间的时间延迟的开发和应用到一个合奏的热点模型,采样范围广泛的参数空间。我们发现,热点模型预测的签名在偏振光,这是在不久的将来直接测量的范围内。然而,我们的估计预测的假设开普勒速度分布内的流的主要部分的磁场是环形的。我们还发现,如果可以为每个源选择正确的吸积流模型(例如,基于磁流体动力学模拟),则黑洞的自旋和倾角可以被限制在自旋倾角空间中的一个小的二维区域。应用该方法的人马座A*(Sgr A*)的近红外偏振数据的结果。它表明,即使与目前可用的数据的Sgr A* 的自旋和倾角可以被约束。下一代近红外和X射线偏振仪应该能够利用这一工具。

英文摘要:

Several massive black holes exhibit flux variability on time scales that correspond to source sizes of the order of few Schwarzschild radii. We survey the potential of near-infrared and X-ray polarimetry to constrain physical properties of such black hole systems, namely their spin and inclination. We have focused on a model where an orbiting hot spot is embedded in an accretion disk. A new method of searching for the time-lag between orthogonal polarization channels is developed and applied to an ensemble of hot spot models that samples a wide range of parameter space. We found that the hot spot model predicts signatures in polarized light which are in the range to be measured directly in the near future. However, our estimations are predicted upon the assumption of a Keplerian velocity distribution inside the flow where the dominant part of the magnetic field is toroidal. We also found that if the right model of the accretion flow can be chosen for each source (e.g. on the basis of magnetohydrodynamics simulations) then the black hole spin and inclination can be constrained to a small two-dimensional area in the spin-inclination space. The results of the application of the method to the available near-infrared polarimetric data of Sagittarius A* (Sgr A*) is presented. It is shown that even with the currently available data the spin and inclination of Sgr A* can be constrained. Next generations of near-infrared and X-ray polarimeters should be able to exploit this tool.

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