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arXiv 0904.3935astro-ph.CO
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各向异性源的引力透镜

Gravitational Lensing of Anisotropic Sources

Rosalba Perna, Charles R. Keeton

摘要:

在强引力透镜中,我们看到的多重图像对应于以稍微不同的方向离开光源的光线。如果源发射是各向异性的,则图像可能不同于传统的透镜预测(其假设各向同性)。为了确定源各向异性可能是重要的尺度,我们研究了从源出现的光线之间的角度δ,对于不同的透镜配置。如果透镜具有幂律分布M propto R^gamma,则角度delta最初随着透镜红移而增加,然后随着zl接近zs而发散(对于陡峭的分布gamma<1)、保持恒定(对于等温分布gamma=1)或消失(对于浅分布gamma>1)。与透镜质量的比例关系大致为Δ propto M^(1/(2-gamma))。NFW剖面的结果在性质上与浅幂律的结果相似,δ峰值大约在源红移的一半(而不是距离的一半)。在实践中,聚束可以改变被大质量星系团透镜化的聚束源的统计数据:对于一个开角θ_jet,有一个概率高达P ~ 0.02-0.07(θ_jet/{0.5} deg)^-1,其中一个透镜化的图像可能会被错过(2 < zs < 6)。活动星系核内的差异吸收可以修改由集群透镜的活动星系核的流量比;由集群透镜的活动星系核的样本可以提供进一步的限制吸收区域的大小。源的各向异性不太可能是星系尺度强透镜效应的显著影响。

英文摘要:

In strong gravitational lensing, the multiple images we see correspond to light rays that leave the source in slightly different directions. If the source emission is anisotropic, the images may differ from conventional lensing predictions (which assume isotropy). To identify scales on which source anisotropy may be important, we study the angle delta between the light rays emerging from the source, for different lensing configurations. If the lens has a power law profile M propto R^gamma, the angle delta initially increases with lens redshift and then either diverges (for a steep profile gamma<1), remains constant (for an isothermal profile gamma=1), or vanishes (for a shallow profile gamma>1) as zl approaches zs. The scaling with lens mass is roughly delta propto M^(1/(2-gamma)). The results for an NFW profile are qualitatively similar to those for a shallow power law, with delta peaking at about half the redshift of the source (not half the distance). In practice, beaming could modify the statistics of beamed sources lensed by massive clusters: for an opening angle theta_jet, there is a probability as high as P ~ 0.02-0.07 (theta_jet/{0.5} deg)^-1 that one of the lensed images may be missed (for 2 < zs < 6). Differential absorption within Active Galactic Nuclei could modify the flux ratios of AGNs lensed by clusters; a sample of AGNs lensed by clusters could provide further constraints on the sizes of absorbing regions. Source anisotropy is not likely to be a significant effect in galaxy-scale strong lensing.

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