摘要
本文提出一个持续供能的喷流—激波模型来解释视超光速射电节点频谱演化的普遍特性．理论计算指出，射电爆发频谱的反转频率νm和频谱极大流量Sm之间的关系具有典型的3阶段演化方式，并且与类星体3C345中观测到的视超光速节点C4的演化行为相当好地符合．令Sm∝ν，则在上升阶段ζ≤3；在平坦变化阶段ζ≈0，而在衰减阶段ζ≈1．爆发幅度和流量极大的迟后时间对频率的关系△Smax（ν）和△t（ν），都具有Blazar天体中观测到的射电爆发的普遍形式．本文提出的激波模型，考虑到驱动气体的持续注入和激波后等离子体的绝热膨胀．因此提供了对相对论喷流中激波形成和演化的物理原因更深入的理解．并对Blazar天体中视超光速节点频谱演化提出了新的解释．
A shock-in-jet model with prolonged supply is proposed to explain the general behaviour of the spectral evolution of superluminal radio knots. It is shown that the thoretical relationship between the turnover frequency vm and the turnover flux density Sm has the typical pattern of 3-stage evolution suggested by Valtaoja et al.(1992) and is well consistent with the evolutionary behaviour observed in the superluminal knot C4 of QSO 3c345.Adopting Sm ∝, we have then (1) at the rising stage, ζ≤-3, (2) at the plateau stage,ζ≈0, and (3) at the decaying stage, ζ≈1. Both the relationships △Smax-νand △t-ν have the general patterns for radio outbursts observed in blazars (△Smax and △t are the maximal burst amplitude and the time delay of flux maximum, respectively). Since the proposed model takes into account of both the prolonged injection of the driving plasma and the adiabatic expansion of the shocked plasma, the growing and decaying stages of the shock are substantiated. The model provides a deeper understanding of the universal spectral evolution of radio outbursts in blazars.
基金
国家自然科学基金
