NGC 1052的推定中心
The putative center in NGC 1052
AI总结：
本研究整合2017年VLBA、GMVA及EHT的观测数据，首次用EHT探测近邻LINER星系NGC 1052的中心区域，测得其尺度、磁场强度等参数，验证了喷流膨胀轮廓的拐点，为喷流形成区的物理性质提供了更严格的约束。
摘要：
许多活动星系都拥有强大的相对论性喷流，然而其形成与加速的详细机制仍未被充分理解。为了以现有最高角分辨率研究喷流加速与准直区域，我们对近邻低电离核发射线区（LINER）星系NGC 1052的双极喷流最内区开展了研究。我们整合了2017年春季一周内使用VLBA（甚长基线阵列）、GMVA（全球毫米波甚长基线干涉测量阵列）和EHT（事件视界望远镜）对NGC 1052的观测数据。EHT首次探测到了NGC 1052，测得两个喷流基底之间中心区域垂直于喷流轴的尺度为250 R_S（史瓦西半径）。该尺度估算结果支持了此前关于喷流膨胀轮廓的研究，即喷流膨胀轮廓在距核心约300 R_S和10000 R_S处存在两个拐点。此外，我们通过对最内辐射特征拟合同步自吸收谱（该特征在约130 GHz处出现谱拐点），估算出距中心引擎22微角秒处的磁场强度为1.25高斯。假设磁场为纯极向，这意味着事件视界处的磁场强度上限为26000高斯，与此前的测量结果一致。NGC 1052的喷流结构复杂、亮度低且为双侧结构，这使得在毫米（mm）波段探测该源颇具挑战。不过，我们的首次EHT观测表明，至少在230 GHz频段下探测该源是可行的。本研究透过致密的环绕环带窥见了喷流形成的最内中心区域，使我们最终得以分辨该区域，并对其膨胀特性与磁场强度给出了更严格的约束。
英文摘要：
Many active galaxies harbor powerful relativistic jets, however, the detailed mechanisms of their formation and acceleration remain poorly understood. To investigate the area of jet acceleration and collimation with the highest available angular resolution, we study the innermost region of the bipolar jet in the nearby low-ionization nuclear emission-line region (LINER) galaxy NGC 1052. We combined observations of NGC 1052 taken with VLBA, GMVA, and EHT over one week in the spring of 2017. For the first time, NGC 1052 was detected with the EHT, providing a size of the central region in-between both jet bases of 250 RS (Schwarzschild radii) perpendicular to the jet axes. This size estimate supports previous studies of the jets expansion profile which suggest two breaks of the profile at around 300 RS and 10000 RS distances to the core. Furthermore, we estimated the magnetic field to be 1.25 Gauss at a distance of 22 μas from the central engine by fitting a synchrotron-self absorption spectrum to the innermost emission feature, which shows a spectral turn-over at about 130 GHz. Assuming a purely poloidal magnetic field, this implies an upper limit on the magnetic field strength at the event horizon of 26000 Gauss, which is consistent with previous measurements. The complex, low-brightness, double-sided jet structure in NGC 1052 makes it a challenge to detect the source at millimeter (mm) wavelengths. However, our first EHT observations have demonstrated that detection is possible up to at least 230 GHz. This study offers a glimpse through the dense surrounding torus and into the innermost central region, where the jets are formed. This has enabled us to finally resolve this region and provide improved constraints on its expansion and magnetic field strength.
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