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

Research output: Contribution to journalArticleScientificpeer-review

Researchers

Research units

  • National Radio Astronomy Observatory Socorro
  • Massachusetts Institute of Technology
  • National Astronomical Observatory of Japan
  • Harvard University
  • CSIC
  • Max Planck Institute for Radio Astronomy
  • National Taiwan University
  • University of Valencia
  • University of Arizona
  • East Asian Observatory
  • Nederlandse Onderzoekschool voor Astronomie
  • California Institute of Technology
  • Academia Sinica Taiwan
  • Institut de Radio Astronomie Millimétrique
  • Radboud University Nijmegen
  • Perimeter Institute for Theoretical Physics
  • University of Waterloo
  • Korea Astronomy and Space Science Institute
  • University of Science and Technology UST
  • University of Chicago
  • Cornell University
  • University of Amsterdam
  • CAS - Shanghai Astronomical Observatory
  • Chinese Academy of Sciences
  • Chalmers University of Technology
  • Graduate University for Advanced Studies
  • University of Naples Federico II
  • Goethe University Frankfurt
  • University of Pretoria
  • Rhodes University
  • Max Planck Institute for Extraterrestrial Physics
  • Universidad de Concepcion
  • Istituto Nazionale di Fisica Nucleare

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.

Details

Original languageEnglish
Article numberL3
JournalAstrophysical Journal Letters
Volume875
Issue number1
Publication statusPublished - 10 Apr 2019
MoE publication typeA1 Journal article-refereed

    Research areas

  • black hole physics, galaxies: individual (M87, 3C279), galaxies: jets, techniques: high angular resolution, techniques: interferometric

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