First M87 Event Horizon Telescope Results. III. Data Processing and Calibration
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 mu as, with characteristic sensitivity limits of similar to 1 mJy on baselines to ALMA and similar to 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 degrees in phase. The M87 data reveal the presence of two nulls in correlated flux density at similar to 3.4 and similar to 8.3 G 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. ; Academy of Finland [274477, 284495, 312496]; European Commission Framework Programme Horizon 2020 Research and Innovation action [731016]; Black Hole Initiative at Harvard University through John Templeton Foundation [60477]; Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT, Chile) [PIA ACT172033, Fondecyt 1171506, BASAL AFB-170002, ALMA-conicyt 31140007]; Consejo Nacional de Ciencia y Tecnologia (CONACYT, Mexico) [104497, 275201, 279006, 281692]; Direccion General de Asuntos del Personal Academico-Universidad Nacional Autonoma de Mexico (DGAPA-UNAM) [IN112417]; European Research Council Synergy Grant "BlackHoleCam: Imaging the Event Horizon of Black Holes" [610058]; Generalitat Valenciana postdoctoral grant [APOSTD/2018/177]; Gordon and Betty Moore Foundation [GBMF 947, GBMF-3561, GBMF-5278]; Japanese Government (Monbukagakusho: MEXT) Scholarship; Japan Society for the Promotion of Science (JSPS) [JP17J08829]; JSPS Overseas Research Fellowships; Key Research Program of Frontier Sciences, Chinese Academy of Sciences (CAS) [QYZDJ-SSW-SLH057, QYZDJ-SSW-SYS008]; Leverhulme Trust Early Career Research Fellowship; MEXT/JSPS KAKENHI [18KK0090, JP18K13594, JP18K03656, JP18H03721, 18K03709, 18H01245, 25120007]; MIT International Science and Technology Initiatives (MISTI) Funds; Ministry of Science and Technology (MOST) of Taiwan [105-2112-M-001-025-MY3, 106-2112-M-001-011, 106-2119-M-001-027, 107-2119-M-001-017, 107-2119-M-001-020, 107-2119-M-110-005]; National Aeronautics and Space Administration (NASA) [80NSSC17K0649]; National Key Research and Development Program of China [2016YFA0400704, 2016YFA0 400702]; National Science Foundation (NSF) [AST-0096454, AST-0352953, AST-0521233, AST-0705062, AST-0905844, AST-0922984, AST-1126433, AST-1140030, DGE-1144085, AST-1207704, AST-1207730]; Natural Science Foundation of China [11573051, 11633006, 11650110427, 10625314, 11721303, 11725312, 11873028, 11873073, U1531245, 11473010]; Natural Sciences and Engineering Research Council of Canada (NSERC); National Research Foundation of Korea [2015-R1D1A1A01056807, NRF-2015H1A2A1033752, NRF-2015H1D3A1066561]; Netherlands Organization for Scientific Research (NWO) VICI award [639.043.513]; Spinoza Prize [SPI 78-409]; Swedish Research Council [2017-00648]; Government of Canada through the Department of Innovation, Science and Economic Development Canada; Province of Ontario through the Ministry of Economic Development, Job Creation and Trade; Russian Science Foundation [17-12-01029]; Spanish Ministerio de Economia y Competitividad [AYA2015-63939-C2-1-P, AYA2016-80889-P]; US Department of Energy (USDOE) through the Los Alamos National Laboratory [89233218CNA000001]; Italian Ministero dell'Istruzione Universita e Ricerca through the grant Progetti Premiali 2012-iALMA [CUP C52I13000140001]; ALMA North America Development Fund; NSF [ACI-1548562, DBI-0735191, DBI-1265383, DBI-1743442]; Smithsonian Institution; Academia Sinica; National Key R&D Program of China [2017YFA0402700]; Science and Technologies Facility Council (UK); CNRS (Centre National de la Recherche Scientifique, France); MPG(Max-Planck-Gesellschaft, Germany); IGN (Instituto Geografico Nacional, Spain); State of Arizona; NSF Physics Frontier Center award [PHY-0114422]; Kavli Foundation; National Science Foundation [PLR-1248097]; NSF Physics Frontier Center [PHY-1125897]; Jansky Fellowship program of the National Radio Astronomy Observatory (NRAO); South African Radio Astronomy Observatory (SARAO), which is a facility of the National Research Foundation (NRF), an agency of the Department of Science and Technology (DST) of South Africa; State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" award [SEV-2017-0709]; European Union' s Horizon 2020 research and innovation programme [730562 RadioNet]; GBMF [GBMF-947]; Compute Ontario; Calcul Quebec; Compute Canada; NSF; CyVerse; [Chandra TM6-17006X]; [AST-1207752]; [MRI-1228509]; [OPP-1248097]; [AST-1310896]; [AST-1312651]; [AST-1337663]; [AST-1440254]; [AST-1555365]; [AST-1715061]; [AST-1615796]; [AST-1716327]; [OISE-1743747]; [AST-1816420]; [AST-1614868] ; This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. 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