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

Abstract

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.

References in corpus (15)

• The NumPy array: a structure for efficient numerical computation
• First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole
• First M87 Event Horizon Telescope Results. VI. The Shadow and Mass of the Central Black Hole
• First M87 Event Horizon Telescope Results. IV. Imaging the Central Supermassive Black Hole
• First M87 Event Horizon Telescope Results. V. Physical Origin of the Asymmetric Ring
• First M87 Event Horizon Telescope Results. II. Array and Instrumentation
• Event-horizon-scale structure in the supermassive black hole candidate at the Galactic Centre
• Jet Launching Structure Resolved Near the Supermassive Black Hole in M87
• 230 GHz VLBI observations of M87: event-horizon-scale structure at the enhanced very-high-energy $\gamma$-ray state in 2012
• The Size, Shape, and Scattering of Sagittarius A* at 86 GHz: First VLBI with ALMA
• The ALMA Phasing System: A Beamforming Capability for Ultra-High-Resolution Science at (Sub)Millimeter Wavelengths
• Calibration of ALMA as a phased array: ALMA observations during the 2017 VLBI campaign
• Generalised warped disk equations
• High gas fraction in a CO-selected main-sequence galaxy at $z>3$
• VLBI detection of the HST-1 feature in the M87 jet at 2 cm

Cited by in corpus (20)

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• First M87 Event Horizon Telescope Results. VI. The Shadow and Mass of the Central Black Hole
• First M87 Event Horizon Telescope Results. IV. Imaging the Central Supermassive Black Hole
• First M87 Event Horizon Telescope Results. II. Array and Instrumentation
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• The Shadow of a Spherically Accreting Black Hole
• Lensing by Kerr Black Holes
• Asymptotic safety casts its shadow
• Higher order corrections to deflection angle of massive particles and light rays in plasma media for stationary spacetimes using the Gauss-Bonnet theorem
• Kinematics of the M87 jet in the collimation zone: gradual acceleration and velocity stratification
• Calibration of ALMA as a phased array: ALMA observations during the 2017 VLBI campaign
• Sparse Modeling in Quantum Many-Body Problems
• Observational signature of a near-extremal Kerr-Sen black hole in the heterotic string theory
• Black Hole Spin Signature in the Black Hole Shadow of M87 in the Flaring State
• Black hole Spin Measurement Based on Time-domain VLBI Observations of Infalling Gas Cloud
• Constraining a black hole companion for M87* through imaging by the Event Horizon Telescope
• Photon Emission Near Myers-Perry Black Holes in the Large Dimension Limit
• Efficient gravitational lens optical scalars calculation of black holes with angular momentum
• rPICARD: A CASA-based Calibration Pipeline for VLBI Data. Calibration and imaging of 7 mm VLBA observations of the AGN jet in M87