摘要
在激变的射电-光学天体(Blazar天体)的观测研究中,偏振辐射特性可提供有关辐射区物理过程的重要情报,在相当多的这类天体中所观测到的射电(或光学)辐射偏振角的快速旋转就是一种非常特别的现象。本文考虑在致密射电源喷流的非轴对称螺旋磁场内传播的相对论性激波所激发的同步加速辐射的偏振角快速旋转的问题。研究表明在β_(ps)～cosθ时(β_(ps)——激波辐射区的速度,θ——视角),偏振角的旋转的最大速率不但和偏振度极小值相对应,也和流量极小值相对应,即偏振角旋转越快,流量和偏振度就越低,这种模型可解释确实观测到的偏振角旋转和偏振度之间的反相关性,但是通常观测到的流量变化与偏振角旋转并不成反相关,不少观测到的偏振角旋转发生在流量极大的附近或流量稳步下降的阶段。对于这些情形,显然必需考虑其它的物理原因,例如,相对论喷流-激波双成份模型可能是一种更好的解释。
The polarization observations of active galactic nuclei, especially BL Lac objects, can provi- de important information about the physical processes in their synchrotron emission regions. The rapid polarization angle swings observed in these objects at radio and optical wavebands is one kind of such important phenomena. In this paper the problem of polarization angle swing is dis- cussed on the basis of the shocked jet model, in which a non-axially symmetric helical mag- netic field is illuminated by a relativistic shock propagating along the jet of the compact radio source. It is shown that, when β_(PS) cosQ (β_(PS)--velocity of the post-shock emitting region, θ--viewing angle), the maximum rate of the polarization angle swing coincides with both the minima of the polarization degree and the flux density, i.e., the faster the polarization angle ro- tates, the lower the polarization degree and the flux density are. This model can explain the anticorrelation between the polarization angle swing and the polarization degree observed in certain compact radio sources. However, variations in flux density usually observed are not an- ticorrelated with the polarization angle swing. In fact, the polarization angle swings observed in a few known compact radio sources usually occurred near the maxima of flux density or during the decreasing phase of flux density. For these cases, other interpretation should be considered For example, the two-component model consisting of the underlying jet and the relativisitic shock within it may be a more suitable model to explain the swing phenomena.
出处
《天文学报》
CSCD
北大核心
1992年第1期14-24,共11页
Acta Astronomica Sinica
关键词
射电源
偏振
相对论
光行差
河外
Extragalactic Radio Sources
Polarization
Relativistic Aberration
