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

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Journal Title
Journal ISSN
Volume Title
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Date
2019-04-10
Major/Subject
Mcode
Degree programme
Language
en
Pages
Series
Astrophysical Journal Letters, Volume 875, issue 1
Abstract
We present the calibration and reduction of Event Horizon Telescope (EHT) 1.3 mm 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 μas, 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° in phase. The M87 data reveal the presence of two nulls in correlated flux density at ∼3.4 and ∼8.3 Gλ 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.
Description
Keywords
black hole physics, galaxies: individual (M87, 3C279), galaxies: jets, techniques: high angular resolution, techniques: interferometric
Other note
Citation
Savolainen, T & Event Horizon Telescope Collaboration 2019, ' First M87 Event Horizon Telescope Results. III. Data Processing and Calibration ', Astrophysical Journal Letters, vol. 875, no. 1, 3 . https://doi.org/10.3847/2041-8213/ab0c57