摘要
本文比较详细地分析了BL Lac天体AO 0235+164中发生的相关射电-光学大爆发的频谱特性(以1975年10月—11月的大爆发为例),并在相对论喷流-激波模型的框架下进行了解释. (1)确定了宁静背景喷流的频谱,并在Konigl喷流模型基础上分析了频谱的结构,讨论了磁场和电子密度的分布及其它有关的参数; (2)在扣除背景喷流的频谱之后,确定了爆发的频谱,表明它可以用一个均匀同步辐射源来表达.光薄的频谱指数α～0.25,断折频率ν_b～3×10^(12) Hz和截断频率()_H～2×10^(14)Hz; (3)讨论了相对论激波绝热加速粒子和放大磁场的特性和爆发辐射区(即激波区)的参数; (4)光学爆发和射电爆发的同时性归因于辐射区的光薄性质.射电光薄频谱指数(α～0.25)比背景喷流频谱相应频段(约10^(12) Hz)上的频谱指数(α_(s2)=0.50)小,这可以用来解释为什么光学变幅比射电变幅大得多; (5)文中还指出,对于光学爆发的尖峰式轮廓和射电爆发的宽阔轮廓之间的差别(例如对于1979年的光学-射电大爆发),可以用喷流中高能电子和磁场沿喷流方向上分布的不均匀性来说明,即沿喷流方向上光学辐射区的尺度比射电辐射区的尺度小得多. 本文的结果认为,AO0235+164中的相关光学—射电爆发是内在的,而不是微引力透镜效应.
A detailed analysis is presented of the spectral properties of the correlated optical and radio outbursts occurred in the BL Lac object AO0235+164, taking the outbursts in Oct.-Nov. 1975 as an example. The observed features can be interpreted reasonably in the frame of relativistic shocked-jet models. (1) The background jet spectrum is determined and its structure is analysed on the basis of Konigl's jet model The distributions of electron density and magnetic field along the jet and other parameters are discussed; (2) With the background jet spectrum subtracted, the spectrum of the outburst is determined. It is shown that it can be represented by a uniform synchrotron radiation source with the optically thin spectral index α～0.25, the break-frequency γ_b～3×10^(12)Hz and the higher cutoff frequency γ_H～2×10^(14)Hz; (3) The adiabatic acceleration of particles and amplification of magnetic field, and the parameters of the emitting regions (i.e. the post-shock regions) are discussed; (4) The simultaneity of the optical and radio outbursts is considered to be due to the optical thinness of the emitting region. The optically thin spectral index at radio band (α～0.25) is smaller than that of the background jet spectrum (α_(52)～0.5) at similar frequencies (～10^(12) Hz), and this can be used to explain the much larger amplitudes of variations at optical band; (5) It is suggested that the difference between the spike profile of optical outburst and the broad profile of radio outburst (as an example, for the correlated optical-radio outbursts in 1979) could be explained by shock propagating through irregularities of energetic electrons and magnetic field along the jet, that is, the scale of the optical emission region along the jet might be much smaller than that of the radio emission region. In summary, the results given here show that the correlated optical-radio outbursts in AO 0235+164 may be intrinsic to the source, not due to gravitational micro-lensing effects.
出处
《天文学报》
CSCD
北大核心
1992年第3期298-308,共11页
Acta Astronomica Sinica
关键词
河外射电源
天体
解释
Extragalactic radio Sources—BL Lac Object—AO0235+164
