Causal connection in parsec-scale relativistic jets: results from the MOJAVE VLBI survey
Causal connection in parsec-scale relativistic jets: results from the MOJAVE VLBI survey
复制标题
DOI：
10.1051/0004-6361/201322203
复制
发表时间：
2013-10-01
影响因子：
6.5
通讯作者：
Zensus, J. A.
中科院分区：
文献类型：
--
作者：
Clausen-Brown, E.;Savolainen, T.;Zensus, J. A.
我们根据来自 133 个 AGN 喷流样本的 15 GHz 甚长基线阵列 (VLBA) 数据报告，活动星系核 (AGN) 喷流在秒差距尺度上存在因果关系。这一结果是通过一种新方法来实现的，该方法根据 AGN 射流通量密度受限样本中测量的表观张角来测量射流洛伦兹因子和固有张角 Gamma theta(j) 的乘积。 Gamma theta(j) 参数对于射流物理学很重要，因为它与射流框架横向膨胀速度以及射流边缘与其对称轴之间的因果关系有关。最重要的是，喷流产生的标准模型要求喷流与其对称轴因果连接，这意味着 Gamma theta(j) 小于或近似于 1。当我们将我们的方法应用于无线电响亮物体的 MOJAVE 通量密度受限样本时，我们发现 Gamma theta(j) 近似于 0.2，这意味着 AGN 喷流是因果连接的。我们还发现证据表明，与离轴更远的射流相比，非常靠近视线观察的活动星系核射流实际上具有更小的固有张角，这与多普勒波束和快速内脊柱/慢速外鞘速度场一致。值得注意的是，伽马射线爆发（GRB）喷流的典型 Gamma theta(j) 高出两个数量级，这表明与 AGN 喷流相比，GRB 喷流中发挥着不同的物理机制。我们的结果的一个有用应用是可以推导出射流的射束参数。假设 AGN 喷流群中的 Gamma theta(j) 近似恒定，则可以使用两个可观测量来确定单个喷流的多普勒因子和洛伦兹因子（因此还有其视角）：表观喷流张角和喷流成分的表观速度。
We report that active galactic nucleus (AGN) jets are causally connected on parsec scales, based on 15 GHz Very Long Baseline Array (VLBA) data from a sample of 133 AGN jets. This result is achieved through a new method for measuring the product of the jet Lorentz factor and the intrinsic opening angle Gamma theta(j) from measured apparent opening angles in flux density limited samples of AGN jets. The Gamma theta(j) parameter is important for jet physics because it is related to the jet-frame sidewise expansion speed and causal connection between the jet edges and its symmetry axis. Most importantly, the standard model of jet production requires that the jet be causally connected with its symmetry axis, implying that Gamma theta(j) less than or similar to 1. When we apply our method to the MOJAVE flux density limited sample of radio loud objects, we find Gamma theta(j) approximate to 0.2, implying that AGN jets are causally connected. We also find evidence that AGN jets viewed very close to the line of sight effectively have smaller intrinsic opening angles compared with jets viewed more off-axis, which is consistent with Doppler beaming and a fast inner spine/slow outer sheath velocity field. Notably, gamma-ray burst(GRB) jets have a typical Gamma theta(j) that is two orders of magnitude higher, suggesting that different physical mechanisms are at work in GRB jets compared to AGN jets. A useful application of our result is that a jet's beaming parameters can be derived. Assuming Gamma theta(j) is approximately constant in the AGN jet population, an individual jet's Doppler factor and Lorentz factor (and therefore also its viewing angle) can be determined using two observable quantities: apparent jet opening angle and the apparent speed of jet components.