Testing general relativity with geodetic VLBI

Abstract

The geodetic VLBI technique is capable of measuring the Sun's gravity light deflection from distant radio sources around the whole sky. This light deflection is equivalent to the conventional gravitational delay used for the reduction of geodetic VLBI data. While numerous tests based on a global set of VLBI data have shown that the parameter γ of the post-Newtonian approximation is equal to unity with a precision of about 0.02 percent, more detailed analysis reveals some systematic deviations depending on the angular elongation from the Sun. In this paper a limited set of VLBI observations near the Sun were adjusted to obtain the estimate of the parameter gamma free of the elongation angle impact. The parameter γ is still found to be close to unity with precision of 0.06 percent, two subsets of VLBI data measured at short and long baselines produce some statistical inconsistency.

Exploring the Asymmetry of the Solar Corona Electron Density with Very Long Baseline Interferometry

“…To fully explore the possibilities that VLBI provides for comparing different solar corona models, there has to be more observational data available, preferably of the likes of AUA020 and AOV022 in terms of the number of observations made close to the Sun and minimum elongation angles. As Titov et al (2018) point out, that requires strong radio sources being close to the Sun, and also large radio telescopes and high data recording rate.…”

“…The AUA020 experiment was held on May 1, 2017 as part of the AUSTRAL program with the purpose of testing general relativity (Titov et al 2018). Two radio sources that were close to the Sun were observed: 0235+164 (1.2 • -1.5 • ) with 452 observations and 0229+131 (2.2 • -2.7 • ) with 577 observations.…”

Earth–Moon very-long-baseline interferometry project: modelling of the scientific outcome

“…Nevertheless, we obtain improvement factor from 4 to 21. A dedicated experiment like (Titov et al 2018) with Earth-Moon VLBI can overcome the presently best accuracy 0.23 • 10 −4 obtained from frequency shift measurements of Cassini spacecraft (Bertotti et al 2003). Epstein & Shapiro (1980) also show that post-post-Newtonian deflection of the Sun is about 11 µarcsec which corresponds to delay equal to 1.1 ps for b = 6 000 km and 67.6 ps for b = 380 000 km.…”

Light Deflection under the Gravitational Field of Jupiter -- Testing General Relativity

“…The plasma of the solar corona has been well studied, but knowledge of plasma in Jupiter's atmosphere is scant. For the Sun, N 0 = 0.57 × 10 12 m −3 with A = 0, which was measured during 2011 and 2012, and this value can be considered a worst case scenario (Soja et al 2014;Titov et al 2018). To describe the electron content within 4 R (corresponding to β ∼ 1.1 • ) from the solar center, additional terms are required (Verma et al 2013;Soja et al 2014).…”

“…with Very Long Baseline Array (VLBA) observations at higher frequency (i.e., 43 GHz) to reduce the light bending by the electron content in the solar corona. The latest accuracy of γ obtained using the VLBI technique is ∼ 9 × 10 −5 (Titov et al 2018). In the above studies, the Sun acts as a gravitational lens (for more of the history of measuring γ, see .…”