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Jet opening angles and gamma-ray brightness of AGN

机译：AGN的喷射口角度和伽马射线亮度

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Aims. We have investigated the differences in apparentopening angles between the parsec-scale jets of the active galacticnuclei (AGN) detected by the Fermi Large Area Telescope during its first three months of operations and those of non-LAT-detected AGN. Methods. We used 15.4GHz VLBA observations of sources fromthe 2cm VLBA MOJAVE program, a subset of which comprises thestatistically complete flux density limited MOJAVE sample. Wedetermined the apparent opening angles by analyzing transverse jetprofiles from the data in the image plane and by applying a modelfitting technique to the data in the (u,v) plane. Both methods provided comparable opening angle estimates. Results. The apparent opening angles of -ray bright blazars are preferentially larger than those of -rayweak sources. At the same time, we have found the two groups to havesimilar intrinsic opening angle distributions, based on a smallersubset of sources. This suggests that the jets in -raybright AGN are oriented at preferentially smaller angles to the line ofsight resulting in a stronger relativistic beaming. The intrinsic jetopening angle and the bulk flow Lorentz factor are found to beinversely proportional, as predicted by standard models of compactrelativistic jets. If a gas dynamical jet acceleration model isassumed, the ratio of the initial pressure of the plasma in the coreregion P0 to the external pressure lies within the range 1.1 to 34.6, with a best fit estimate of .Key words: galaxies: active - galaxies: jets - quasars: general - radio continuum: galaxies
机译：目的我们已经研究了费米大面积望远镜在运行的前三个月与非LAT探测到的AGN所探测到的活动银河核（AGN）的等距尺度射流之间的视在打开角度的差异。方法。我们使用了来自2cm VLBA MOJAVE程序的源的15.4GHz VLBA观测值，该子集包括统计上完整的磁通密度受限的MOJAVE样本。通过从图像平面中的数据分析横向射流轮廓，并对（u，v）平面中的数据应用模型拟合技术，确定了视在打开角度。两种方法都提供了可比较的张角估计。结果。 -ray明亮的blazar的视在打开角度优先大于-rayweak的源的显着打开角度。同时，基于较小的源子集，我们发现两组具有相似的固有打开角度分布。这表明，在明亮的AGN中，射流相对于视线的角度优选偏小，从而导致相对论性较强的射束。正如紧凑相对论射流的标准模型所预测的那样，发现固有的射流张开角和整体流量洛伦兹因子成反比。如果假设气体动力学射流加速模型，则核心区域P0中等离子体的初始压力与外部压力的比值在1.1至34.6的范围内，最佳拟合估计值为。关键词：星系：活跃星系：喷气机-类星体：一般-连续射电：星系

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