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## Testing general relativity with geodetic VLBI. What a single, specially designed experiment can teach us

Astronomy and Astrophysics, Volume 618, A8 (2018)

Keywords: astrometry, techniques: interferometric, gravitation

### Abstract

Context. We highlight the capabilities of geodetic VLBI technique to test general relativity in the classical astrometric style, i.e. measuring the deflection of light in the vicinity of the Sun. Aims. In previous studies, the parameter γ was estimated by global analyses of thousands of geodetic VLBI sessions. Here we estimate γ from a single session where the Sun has approached two strong reference radio sources, 0229+131 and 0235+164, at an elongation angle of 1–3°. Methods. The AUA020 VLBI session of 1 May 2017 was designed to obtain more than 1000 group delays from the two radio sources. The solar corona effect was effectively calibrated with the dual-frequency observations even at small elongation. Results. We obtained γ with a greater precision ($0.9 × 10^{−4}$) than has been obtained through global analyses of thousands of standard geodetic sessions over decades. Current results demonstrate that the modern VLBI technology is capable of establishing new limits on observational tests of general relativity.