VLBA Observations of Neutrino-Candidate Blazars

在过去的四年里，观测证据开始堆积起来，表明冰立方天文台探测到的一些高能宇宙中微子可能与blazar有关。事实上，这些从活动星系核中心喷出并以小角度指向我们视线的强大喷流，长期以来一直被预测为明亮的中微子发射器，并展示出足够平坦的中微子光谱，在大约100TeV以上的足够高的能量下超过大气背景。最突出的例子是TXS0506056源，它与2017年9月探测到的高能冰立方中微子具有3西格玛意义。在所有后来的中微子-blazar组合中，最高置信度的组合是2019年7月探测到的与blazar PKS1502 106位置一致的“黄金警报”中微子。我们在对甚长基线阵列(VLBA)的两个不同提议中成功地提出了对TXS 0506 056和PKS 1502106的甚长基线干涉测量(VLBI)观测。在中微子探测到15 GHz至86 GHz的多个频率和全极化模式后不久，成功地进行了两个目标源的观测。这项提议的目的是获得资金，用于对所产生的观测数据进行全面分析，以研究两个候选中微子耀斑的VLBI喷流结构的总强度和极化，并利用我们的观测和来自Mojave计划的补充数据，跟踪中微子事件后它们射电喷流在毫弧秒尺度上的演变。VLBI的数据和分析将用于研究blazar中微子发射模型，在该模型中，伽马辐射和中微子产生都在结构射流的两区模型中得到解释。这些模型将被测试，它们可能的参数范围将受到我们的VLBI数据和互补的多波长数据的限制。

In the past four years, observational evidence has started piling up that some high-energy cosmic neutrinos detected by the IceCube observatory may be associated with blazars. Indeed, these powerful jets ejected from the centers of active galactic nuclei and pointed at a small angle to our line of sight have long been predicted to be bright neutrino emitters and to exhibit a neutrino spectrum flat enough to exceed the atmospheric background at sufficiently high energies above about 100 TeV. The most prominent example is the source TXS0506+056 that has been associated at 3-sigma significance with a high-energy IceCube neutrino detected in September 2017. Among all later neutrino-blazar associations, the highest-confidence one is represented by a 'gold-alert' neutrino detected in July 2019 in positional coincidence with the blazar PKS1502+106. We have successfully proposed for Very-Long-Baseline Interferometry (VLBI) observations of TXS 0506+056 and PKS 1502+106 in two separate proposals to the Very Long Baseline Array (VLBA). The observations of the two target sources were successfully performed shortly after the neutrino detections at multiple frequencies between 15 GHz and 86 GHz and in full polarization mode. The goal of this proposal is to obtain funding for a full analysis of the resulting observational data to study the VLBI jet structure of the two candidate neutrino blazars in total intensity and polarisation and to follow up on the evolution of their radio jets on milliarcsecond scales after the neutrino events using our observations and complementary data from the MOJAVE program. The VLBI data and analysis will be used to study blazar neutrino-emission models in which both the gamma radiation and the neutrino production are explained in a two-zone model of a structured jet. These models will be tested and their possible parameter ranges will be constrained by our VLBI data and complementary multi wavelength data.