相对论性球对称大质量风的观测现象
Observational Appearance of Relativistic, Spherically Symmetric Massive Winds
摘要：
光子在相对论运动介质中的平均自由程沿下游方向变长，而沿上游方向变短。结果，观测到的光学深度$τ$在下游方向上变小，而在上游方向上变大。因此，如果一个相对论性的球形风吹走，光学深度强烈地依赖于它的速度和速度与视线之间的角度。Abramowicz等人（1991年）研究了这种相对论风，发现在非相对论情况下，$τ=1$的光球形状呈凸面，但在相对论速度下呈凹面。我们进一步计算了光球层在共动系和惯性系中的温度分布和光度。我们发现，在相对论区域，边缘暗化效应会发生强烈的修正。我们还发现，由于相对论效应，光球的光度随着风速的增加而变大。此外，在惯性系中的光度比在共动系中的高。这些结果表明，当存在强相对论风时，观测到的发光物体的温度和亮度可能被高估。
英文摘要：
The photon mean free path in a relativistically moving medium becomes long in the down-stream direction while short in the up-stream direction. As a result, the observed optical depth $τ$ becomes small in the downstream direction while large in the upstream direction. Hence, if a relativistic spherical wind blows off, the optical depth depends strongly on its speed and the angle between the velocity and the line-of-sight. Abramowicz et al. (1991) examined such a relativistic wind, and found that the shape of the photosphere at $τ=1$ appears convex in the non-relativistic case, but concave for relativistic velocities. We further calculated the temperature distribution and luminosity of the photosphere both in the comoving and inertial frames. We found that the limb-darkening effect would strongly modified in the relativistic regime. We also found that luminosities of the photosphere becomes large as the wind speed increases due to the relativistic effects. In addition, the luminosity in the inertial frame is higher than that in the comoving frame. These results suggest that the observed temperature and brightness in luminous objects may be overestimated when there are strong relativistic winds.
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