EHT 2018

April 2018 VLBI Campaign Data

The Event Horizon Telescope Collaboration (EHTC) and Joint ALMA Observatory (JAO) announce the public data release of the Very Long Baseline Interferometry (VLBI) 1-mm 2018 observations by the Event Horizon Telescope (EHT).  The overall goal of these observations were continued imaging of the supermassive black holes M87* and Sagittarius A* at event horizon scales and to image the AGNs  OJ 287, Cen A and 4C 01.28 (1055+018) at high angular resolution.

Public release data packages are available from CyVerse Data Common (10.25739/v7hh-6244) and the ALMA Science Portal.

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This data delivery contains what is defined by the EHTC as L1 data for the 2018 observing campaign.  The 2018 campaign was the second where the Atacama Large Millimeter/submillimeter Array (ALMA) participated as a phased array, a capability that was developed by the ALMA Phasing Project. The EHT L1 data encompass the VLBI correlator output, converted to a circular polarization basis, as well as the calibration information from the participating telescopes.  For ALMA this includes the quality assurance (QA2) output that was used for the polarization basis conversion.  A primary reference for the processing of EHT data is Event Horizon Telescope Collaboration et al. 2019, ApJL, 875, L3 (doi: 10.3847/2041-8213/ab0c57). For scientific results derived from the EHT 2018 April Observation Campaign see eventhorizontelescope.org/publications. Additional data products derived from these L1 data can be found at eventhorizontelescope.org/for-astronomers/data.

This data delivery includes observations from the following facilities: ALMA, the Atacama Pathfinder Experiment (APEX), the Submillimeter Telescope (SMT), the James Clerk Maxwell Telescope (JCMT), the Large Millimeter Telescope Alfonso Serrano (LMT), the IRAM 30m telescope, the Submillimeter Array (SMA), the South Pole Telescope (SPT), the Greenland Telescope (GLT), the Northern Extended Millimeter Array (NOEMA) and the Kitt Peak 12m (KP).  More information about these facilities can be found in Event Horizon Telescope Collaboration et al. 2019, ApJL, 875, L2 (doi: 10.3847/2041-8213/ab0c96).

October 2018 Band 7 and VLBI Test Data

Moving to true sub-millimeter VLBI began with ALMA-only phasing tests over several years and under a variety of conditions and a short VLBI test session conducted in October 2018.  These observations are described in detail in “A Characterization of the ALMA Phasing System at 345 GHz” published at Crew, G. B., Goddi, C., Matthews, L. D., et al. 2023, Publications of the Astronomical Society of the Pacific, 135, 025002, doi: 10.1088/1538-3873/acb348.  This paper also discusses additional observations conducted earlier and later to further characterize the Band 7 capability which was eventually offered in Cycle 9.

Public release data packages are available through the ALMA Science Portal.

Project Codes:

The VLBI observations were planned in two sessions with the EHT: one session using an Eastern sub-array (NOEMA, IRAM-30m, GLT, APEX and ALMA) and another using a Western sub-array (SMA, GLT, APEX and ALMA) and were intended only to obtain fringes.  Therefore no calibration observations were performed.  Owing to marginal weather conditions, VLBI fringes were obtained only  on Oct 18-19 in the Eastern sub-array and on Oct 21 in the Western sub-array.  More details on the VLBI results are found in the paper “First Very Long Baseline Interferometry Detections at 870 µm” accepted for publication in the Astronomical Journal in 2024.