Blazar喷流节点运动视速度的统计研究

Studying the Apparent Velocity of Blazar jet Statistically

VLBI观测表明,TeV伽马射线Blazar(耀变体)的喷流运动视速度远小于MeV/GeV伽马射线Blazar,然而TeV伽马射线辐射流量的快速变化却要求这些Blazar的相对论喷流速度与MeV/GeV Blazar的相当.对于这一矛盾,目前有多种解释.为了检验这些模型,我们收集了VLBI对Blazar喷流运动的监测数据,样本包括86个FSRQs(平谱射电类星体)、22个BL Lac天体,共108个Blazar;从统计上研究了,该样本中各Blazar最大视速度喷流节点的位置与射电光度相关关系.结果表明,Blazar最大视速度喷流节点的位置与射电光度有较强的相关关系,随着Blazar射电光度的减小,喷流中最大视速度VLBI节点的位置到VLBI核的距离逐渐变小.这意味着:TeV伽马源(低光度Blazar)的喷流减速区距离VLBI核较近,喷流从高能辐射区到VLBI可分辨尺度已经减速,支持减速喷流模型对TeV伽马射线Blazar上述矛盾的解释.

VLBI observations show that the radio knots of TeV gamma-ray Blazar jets move much more slowly than MeV/GeV gamma-ray Blazar jets. But their violent variations of TeV fluxes require Lorentz factors of their relativistic jets similar to those of MeV/GeV Blazars. There are several models to explain this problem, for example, the deceleration jet model in which it is assumed that radio knots decelerate from the sub-parsec scale to the parsec scale in the jet, and the transverse structure model in which it is assumed that the jet is not a symmetrical structure but a transverse structure. In order to test these models, we collect the VLBI observations for a sample of Blazars. Totaly, the sample consists of 108 Blazars （86 FSRQs and 22 BL Lac objects）. We calculate the apparent speed of all radio knots in the sample and statistically study the locations of knots with the maximum apparent speed of each Blazar in the sample. The results show that the location of the radio knots with the maximum apparent speed decreases with the decrease of the radio luminosity of Blazars, from FSRQs to LBLs to IBLs to HBLs, with the radio luminosity decreases, the distance of the radio knots with the maximum apparent speed from the core in the plane of sky gets shorter and shorter, implying that HBL jets have the shortest accelerate region. That is to say, the jet decelerating region locates near the core in Blazar with low luminosity, and the jet has decelerated from TeV-emitting region to the scale that VLBI can resolve, consistent with the deceleration model.