非相干同步辐射源的最大亮度温度：逆康普顿极限--一个误称
Maximum Brightness Temperature of an Incoherent Synchrotron Source : Inverse Compton Limit - a Misnomer
摘要：
我们表明，非相干同步辐射源的峰值亮度温度的上限为~ 10^{12} K，在文献中通常被称为逆康普顿极限，可能并不真正是由于逆康普顿效应。我们指出，对于辐射粒子和磁场能量均分的条件，实际上得到了一个更严格的极限T_{eq} ~ 10^{11}，这恰好是自吸收同步辐射源的最小能量位形。从T_{eq}向任一方向的亮温变化一个数量级，都需要偏离均分约8个数量级，这意味着系统总能量的变化高达均分值的~ 10^{4}倍。这种极端的能量变化的限制意味着亮度温度可能不会偏离T_{eq}太多。这是支持的事实，在光谱周转，亮度温度远低于~ 10^{11} K也没有看到VLBI观测。特别是更高的亮度温度，在源中不仅需要许多数量级的相对论粒子的额外能量，而且还需要许多数量级的较弱磁场。反磁效应不允许这样的极端条件，保持亮度温度接近均分值，这远低于逆康普顿效应变得重要的极限。
英文摘要：
We show that an upper limit of ~ 10^{12} K on the peak brightness temperature for an incoherent synchrotron radio source, commonly referred to in the literature as an inverse Compton limit, may not really be due to inverse Compton effects. We show that a somewhat tighter limit T_{eq} ~ 10^{11} is actually obtained for the condition of equipartition of energy between radiating particles and magnetic fields which happens to be a configuration of minimum energy for a self-absorbed synchrotron radio source. An order of magnitude change in brightness temperature from T_{eq} in either direction would require departures from equipartition of about eight orders of magnitude, implying a change in total energy of the system up to ~ 10^{4} times the equipartition value. Constraints of such extreme energy variations imply that brightness temperatures may not depart much from T_{eq}. This is supported by the fact that at the spectral turnover, brightness temperatures much lower than ~ 10^{11} K are also not seen in VLBI observations. Higher brightness temperatures in particular, would require in the source not only many orders of magnitude higher additional energy for the relativistic particles but also many order of magnitude weaker magnetic fields. Diamagnetic effects do not allow such extreme conditions, keeping the brightness temperatures close to the equipartition value, which is well below the limit where inverse Compton effects become important.
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