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 the observations is to image the supermassive black holes M87 (M87) and Sagittarius A (SGRA) at event horizon scales and to image the AGNs OJ287, CENA and blazar 4C +-1.28 (B1055+018, J1058+015) at high resolution.
This data delivery contains what is defined by the Event Horizon Telescope Collaboration (EHTC) as L1 data for the Very Long Baseline Interferometry (VLBI) 1-mm 2018 observing campaign by the Event Horizon Telescope (EHT). The 2018 campaign was the second where the Atacama Large Millimeter Array (ALMA) participated as a phased array, a capability that was developed by the ALMA Phasing Project (APP; Doeleman 2010; Fish et al. 2013; Matthews et al. 2018). The EHT L1 data encompasses the VLBI correlator output, converted into circular polarization basis, as well as the calibration information from the participating telescopes. For ALMA this includes their quality assurance (QA2) output that is used for the polarization basis conversion. The primary reference for the data from the EHT 2018 April observation campaign is Event Horizon Telescope Collaboration et al. (2024). The paper in detail discusses the processing carried out for the current L1 data delivery. Aspects that are the same as the EHT 2017 April campain are described in more detail in Event Horizon Telescope Collaboration et al. (2019). For scientific results derived from the EHT 2018 April Observation Campaign see https://eventhorizontelescope.org/publications. Additional data products derived from this L1 data can be found at https://eventhorizontelescope.org/for-astronomers/data.
This data delivery includes data 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 phased Submillimeter Array (SMA), the South Pole Telescope (SPT), and the Greenland Telescope (GLT). More information about the facilities used for these observations can be found in Event Horizon Telescope Collaboration et al. (2024).