First Very Long Baseline Interferometry Detections at 870μm

Kavli Affiliate: Bradford A. Benson

| First 5 Authors: Alexander W. Raymond, Sheperd S. Doeleman, Keiichi Asada, Lindy Blackburn, Geoffrey C. Bower

| Summary:

The first very long baseline interferometry (VLBI) detections at 870$mu$m
wavelength (345$,$GHz frequency) are reported, achieving the highest
diffraction-limited angular resolution yet obtained from the surface of the
Earth, and the highest-frequency example of the VLBI technique to date. These
include strong detections for multiple sources observed on inter-continental
baselines between telescopes in Chile, Hawaii, and Spain, obtained during
observations in October 2018. The longest-baseline detections approach
11$,$G$lambda$ corresponding to an angular resolution, or fringe spacing, of
19$mu$as. The Allan deviation of the visibility phase at 870$mu$m is
comparable to that at 1.3$,$mm on the relevant integration time scales between
2 and 100$,$s. The detections confirm that the sensitivity and signal chain
stability of stations in the Event Horizon Telescope (EHT) array are suitable
for VLBI observations at 870$mu$m. Operation at this short wavelength,
combined with anticipated enhancements of the EHT, will lead to a unique high
angular resolution instrument for black hole studies, capable of resolving the
event horizons of supermassive black holes in both space and time.

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