耀变体光学波段的微光变及能谱变化

Microvariability and Spectral Variability in the Optical Bands of Blazars

耀变体在多个波段的微光变和能谱变化多年来是中外天文观测研究的热点课题。耀变体的微光变于20世纪60年代被发现,20世纪80年代以来发现很多源的微光变具有不同的特性,目前对其物理机制的认识和理论、模型的研究还处于发展阶段。该文总结了7个目前观测最多的耀变体(3C 66A,3C 279,3C 454.3,AO 0235+164,BL Lac,OJ 287,S5 0716+714)在光学波段的微光变和能谱变化的观测历史和最新进展,并对其理论模型作了简单介绍。

Microvariability across the whole electromagnetic spectrum in blazars was first discovered in 1960s. It began to get extensive attention in 1980s. After twenty years＇ investigation, the physical mechanism leading to microvariability has not been found. Several models exist in explaining this phenomenon in the literature. The most widely accepted one is the shock- in-jet model. In this model, shocks propagating along the relativistic jet and interacting with the hydrodynamically turbulent plasma and twisted magnetic field should be responsible for the microvariability. Spectral variability is always found when a blazar shows variability in brightness in both short and long timescale. There are many different phenomena. Some blazars, generally flat spectrum radio quasars, become redder when brighter. Some （generally BL Lac objects） show the opposite trend-bluer when brighter. Some show no spectral variability at all. When blazars are in different states, they exhibit different behavior in spectral variability. As an example, in the outburst of OJ 287 in 1994, it showed no color change at all. However, in its 2005 outburst, it was observed to be bluer when brighter. Another example is S5 0716＋714, it has been observed to be bluer when brighter, redder when brighter as well as show no spectral change with brightness. This paper provides a comprehensive review of the historical study of microvariability as well as spectral variability of seven most extensively observed blazars, namely 3C 279, 3C 454.3, 3C 66A, AO 0235＋164, BL Lac, OJ 287, S5 0716＋714. Models for these blazars＇ variability are also simply introduced.