激变射电源中偏振角快速旋转的解释

在许多激变射电源(Blazar天体)中,观测到一种非常特别的现象,即偏振角的快速旋转.在相对论喷流的框架下,这种偏振角的旋转可以用双成分模型来解释.在这个模型中,一个成分是作为背景喷流本身的辐射,是恒定不变的成分;另一个成分被认为是沿喷流传播的相对论性激波,它产生变化的流量和偏振.这两个成分的偏系辐射的叠加可以产生观测到的偏振角旋转。本文讨论了三个激变射电源(BL Lac,AO0235+164,0727-115)中发生的偏振角旋转.结果表明,用相对论喷流-激波双成分模型可以很好地拟合观测到的偏振角旋转、偏振度和流量变化。说明射电激变源中出现的快速偏振和流量变化可能是由于相对论激波沿喷流传播时,激波辐射区中磁场取向和有序性以及强度和电子密度的变化所引起的。

An Interpretation for Polarization Angle Swings in Rapidly Variable Radio Sources

Polarization angle swings usually observed in rapidly variable radiio sources (especially BL Lac objects) are a distinct phenomenon, which can provide important information about the synchrotron emission regions, especially about the magnetic fields. In the frame of relativis-tic jet model, this kind of phenomenon can be explained hi terms of two-component model, in which one component is identified as the underlying jet giving rise to the stable background-level emission, and the other component is assumed to be the relativistic shock propagating along the jet and giving rise to the variable flux density and plarization. The combination of these two components can produce the polarization angle swings and the related variations observed in flux density and polarization degree. In this paper three events of polarization angle swing observed in three BL Lac objects (BL Lac, A00235 + 164 and 0727-115) are discussed. It is shown that the relativistic jet-shock two-component model suggested can well fit the observed polarization angle swings and the variations in both flux density and polarization degree for all the three BL Lac objects. This seems to mean that the rapid variations in polarization and flux density observed in th BL Lac objects may be due to the relativistic shocks propagatimg along the jets, especially th t the polarization angle swings may be due to the rotations of the magnetic fields in the jets.