引力透镜如何帮助gamma-ray光子避免$γ- γ$吸收
How gravitational lensing helps gamma-ray photons avoid $γ- γ$ absorption
摘要：
我们调查潜在的$γ-γ$吸收的伽玛射线辐射耀变体所产生的不均匀性沿视线，超出了弥漫的河外背景光（EBL）。作为多余$γ-γ$不透明度的合理来源，我们考虑（1）前景星系，包括这种配置导致强引力透镜的情况，（2）这些前景星系中的单个恒星，以及（3）我们自己星系中的单个恒星，它们可能充当微透镜事件的透镜。我们发现，接近视线的介入星系不太可能导致显著的过量$γ-γ$吸收。这开辟了探测能量超过10 GeV的透镜伽马射线耀变体的前景，其伽马射线光谱有效地只受EBL的影响。最明亮的恒星要么位于干预星系，要么位于我们的星系，提供了一个环境，在这个环境中，这些伽马射线原则上可以被显著吸收。然而，尽管由于恒星位于居间星系中，伽马射线有很大的微透镜概率，但伽马射线通过被这些居间恒星的引力势偏转到投影距离（“碰撞参量”）而避免吸收，在投影距离处，所产生的$γ-γ$不透明度可以忽略不计。因此，即使在背景耀变体和前景恒星或星系之间的排列非常接近的情况下，这里考虑的两个介入的多余光子场都不能提供超出EBL的多余$γ-γ$不透明度的实质性来源。
英文摘要：
We investigate potential $γ-γ$ absorption of gamma-ray emission from blazars arising from inhomogeneities along the line of sight, beyond the diffuse Extragalactic Background Light (EBL). As plausible sources of excess $γ-γ$ opacity, we consider (1) foreground galaxies, including cases in which this configuration leads to strong gravitational lensing, (2) individual stars within these foreground galaxies, and (3) individual stars within our own galaxy, which may act as lenses for microlensing events. We found that intervening galaxies close to the line-of-sight are unlikely to lead to significant excess $γ-γ$ absorption. This opens up the prospect of detecting lensed gamma-ray blazars at energies above 10 GeV with their gamma-ray spectra effectively only affected by the EBL. The most luminous stars located either in intervening galaxy or in our galaxy provides an environment in which these gamma-rays could, in principle, be significantly absorbed. However, despite a large microlensing probability due to stars located in intervening galaxies, gamma-rays avoid absorption by being deflected by the gravitational potentials of such intervening stars to projected distances ("impact parameters"') where the resulting $γ-γ$ opacities are negligible. Thus, neither of the intervening excess photon fields considered here, provide a substantial source of excess $γ-γ$ opacity beyond the EBL, even in the case of very close alignments between the background blazar and a foreground star or galaxy.
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