First M87 Event Horizon Telescope Results. III. Data Processing and Calibration

Understand

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.