Large-Scale Blazar Jets: Clues on High-Energy Emission from Low-Frequency Radio Observations

100多个活动星系核喷流在光学和X射线波段以弧秒分辨率进行了成像。在低功率FR I源的情况下，X射线喷射发射通常可以被解释为射电同步加速器谱的延伸。与此形成对比的是，FR II喷流的射电、光学和X射线宽带光谱清楚地表明，还有其他发射过程在起作用。最初提出的是CMB光子的逆康普顿化(IC/CMB)。这个模型需要在千帕秒尺度上的整体相对论运动(这很难观察到)，以及向下延伸到小于∼100的洛伦兹因子的电子能量分布，这低于像VLA这样的GHz仪器追踪的能量区域。最近，对涉及数百兆赫国际基线的活动星系核喷流进行的高分辨率LOFAR观测的第一批结果发现，一个类星体的射电流量密度远低于通过外推GHz谱估计的值，因此无法用IC/CMB模型解释观测到的X射线结发射。在这个项目中，我们将在千帕秒尺度上对类星体喷流的长波射电发射进行系统的LOFAR研究，并将其与短波射电和高能光学和X射线宽带光谱数据相结合，以测试IC/CMB和替代发射模型。我们将利用LOFAR-VLBI技术进一步开发和优化低、超低射电总频率和线偏振强度下的高分辨率成像技术，以测量磁场几何形状并约束喷流组成和发射模型。

More than 100 AGN jets have been imaged with arcsec resolution in the optical and X-ray band. In the case of low-power FR I sources, the X-ray jet emission can generally be interpreted as an extension of the radio synchrotron spectrum. In contrast to this, the radio, optical and X-ray broadband spectra of FR II jets clearly show that other emission processes are at play. Originally, inverse-Comptonization of CMB photons (IC/CMB) was suggested. This model requires bulk relativistic motion on kiloparsec scales (which is difficult to observe) and an electron energy distribution extending down to Lorentz factors smaller than ∼100, which is lower than the energy regimes traced by GHz instruments like the VLA. Very recently, first results of high-resolution LOFAR observations of AGN jets involving international baselines at hundreds of MHz found radio flux densities in one quasar well below the values estimated by extrapolating the GHz spectra and thus falling short of explaining the observed X-ray knot emission in terms of the IC/CMB model. In this project, we will perform a systematic LOFAR study of the long-wavelength radio emission of quasar jets on kiloparsec scales and combine this with shorter-wavelength radioand higher-energy optical and X-ray broadband spectral data to test the IC/CMB and alternative emission models. We will further develop and optimize high-resolution imaging techniques at the low and ultralow radio frequencies in total and linearly-polarized intensity with LOFAR-VLBI techniques to measure magnetic-field geometries and constrain jet-composition and emission models.