# Calibration of ALMA as a phased array: ALMA observations during the 2017 VLBI campaign

## TL;DR

This paper details the calibration procedures for using ALMA as a phased array in VLBI mode, demonstrating their application during the 2017 global VLBI campaigns with first science results.

## Contribution

It introduces specialized calibration and quality assurance procedures enabling ALMA to function as a fully calibrated VLBI station, a novel capability demonstrated during the 2017 campaigns.

## Key findings

- Successful VLBI observations with ALMA at 3mm and 1.3mm bands.
- First science results from ALMA as a phased array in VLBI.
- Validated calibration procedures for future VLBI observations.

## Abstract

We present a detailed description of the special procedures for calibration and quality assurance of Atacama Large Millimeter/submillimeter Array (ALMA) observations in Very Long Baseline Interferometry (VLBI) mode. These procedures are required to turn the phased ALMA array into a fully calibrated VLBI station. As an illustration of these methodologies, we present full-polarization observations carried out with ALMA as a phased array at 3mm (Band 3) and 1.3mm (Band 6) as part of Cycle-4. These are the first VLBI science observations conducted with ALMA and were obtained during a 2017 VLBI campaign in concert with other telescopes worldwide as part of the Global mm-VLBI Array (GMVA, April 1-3) and the Event Horizon Telescope (EHT, April 5-11) in ALMA Bands 3 and 6, respectively.