第一个M87事件视界望远镜的结果。III。数据处理和校准
First M87 Event Horizon Telescope Results. III. Data Processing and Calibration
摘要：
我们介绍了事件视界望远镜（EHT）1.3毫米射电波长观测的校准和还原，该观测是在2017年4月5日至11日的观测活动期间，在射电星系M87和类星体3C 279的中心进行的超大质量黑洞候选者。这些全球甚长基线干涉观测首次包括高灵敏度的阿塔卡马大型毫米/亚毫米阵列（ALMA）;其角分辨率达到25微秒，ALMA基线的特征灵敏度极限为~1 mJy，其他基线的特征灵敏度极限为~10 mJy。这些观测结果对现有的数据处理工具提出了挑战，这些挑战来自快速的大气相位波动、宽的记录带宽和高度异质的阵列。作为回应，我们开发了三个独立的管道相位校准和条纹检测，每一个量身定制的EHT的特定需求。最终的数据产品包括校准的总强度振幅和相位信息。它们通过一系列质量保证测试进行验证，这些测试显示了整个管道的一致性，并将基线系统误差限制为幅度2%和相位1度。M87的数据揭示了在~3.4和~8.3千兆-λ的相关通量密度中存在两个零值，以及闭合量的时间演化，表明在几天的时间尺度上紧凑结构的内在变化，或者几十亿太阳质量的黑洞的几个光交叉时间。这些测量提供了第一个机会，以图像的水平尺度结构在M87。
英文摘要：
We present the calibration and reduction of Event Horizon Telescope (EHT) 1.3mm radio wavelength observations of the supermassive black hole candidate at the center of the radio galaxy M87 and the quasar 3C 279, taken during the 2017 April 5-11 observing campaign. These global very long baseline interferometric observations include for the first time the highly sensitive Atacama Large Millimeter/submillimeter Array (ALMA); reaching an angular resolution of 25 micro-as, with characteristic sensitivity limits of ~1 mJy on baselines to ALMA and ~10 mJy on other baselines. The observations present challenges for existing data processing tools, arising from the rapid atmospheric phase fluctuations, wide recording bandwidth, and highly heterogeneous array. In response, we developed three independent pipelines for phase calibration and fringe detection, each tailored to the specific needs of the EHT. The final data products include calibrated total intensity amplitude and phase information. They are validated through a series of quality assurance tests that show consistency across pipelines and set limits on baseline systematic errors of 2% in amplitude and 1 degree in phase. The M87 data reveal the presence of two nulls in correlated flux density at ~3.4 and ~8.3 giga-lambda and temporal evolution in closure quantities, indicating intrinsic variability of compact structure on a timescale of days, or several light-crossing times for a few billion solar-mass black hole. These measurements provide the first opportunity to image horizon-scale structure in M87.
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