Observational and Theoretical Studies of Variability in Compact Extragalactic Sources

在致密的河外射电源中观察到的变化将从观测和理论两方面进行研究。这些变化既表现为甚长基线干涉测量(VLBI)研究揭示的结构变化，也表现为总通量密度的变化。VLBI技术将被用来监测两个类星体，4C39.25和NRAO 140，这两个类星体正在发生特别有趣的变化，这也可能导致对以前观察到的现象的新理解。将对观察到的类星体和类似源中的可变性进行理论解释的调查。包含激波在相对论喷流中湍流区域传播的模型似乎能够解释观测到的变化的一般特征，特别是变化时间尺度的频率依赖性。对湍流射流中激波的发射模式和频谱进行了数值计算，并与观测数据进行了比较。拟议项目的最终目标是更好地了解类星体中高速紧凑型喷气式飞机的性质和来源，并通过这一点了解这些天体中的“中央引擎”的性质。

The variations observed in compact extragalactic radio sources will be investigated both observationally and theoretically. These variations manifest themselves as changes both in the structure as revealed by very-long baseline interferometry (VLBI)studies and in the total flux density. The VLBI technique will be used to monitor two quasars, 4C39.25 and NRAO 140, which are under going particularly interesting variations which may also lead to new understandings of phenomena previously observed. Investigations of theoretical explanations for the observed variability in quasars and similar sources will be carried out. Models involving shock waves propagating through turbulent regions in relativistic jets appear capable of explaining the general characteristics of the observed variations, especially the frequency dependence of the variability timescales. Numerical calculations of emission patterns and spectra of shocks in turbulent jets will be performed and compared with the observational data. The ultimate goal of the proposed project is to better understand the nature and origin of high-speed compact jets in quasars, and through this the nature of the "central engine" in these objects.