Abstract
Abstract We measured the relative positions between two pairs of compact extragalactic sources (CESs), J1925-2219 and J1923-2104 (C1–C2) and J1925-2219 and J1928-2035 (C1–C3), on 2020 October 23–25 and 2021 February 5 (totaling four epochs), respectively, using the Very Long Baseline Array at 15 GHz. Accounting for the deflection angle dominated by Jupiter, as well as the contributions from the Sun and planets other than Earth, the Moon, and Ganymede (the most massive of the solar system’s moons), our theoretical calculations predict that the dynamical ranges of the relative positions across four epochs in R.A. of the C1–C2 pair and C1–C3 pair are 841.2 and 1127.9 μas, respectively. The formal accuracy in R.A. is about 20 μas, but the error in decl. is poor. The measured standard deviations of the relative positions across the four epochs are 51.0 and 29.7 μas in R.A. for C1–C2 and C1–C3, respectively. These values indicate that the accuracy of the post-Newtonian relativistic parameter, γ, is ∼0.061 for C1–C2 and ∼0.026 for C1–C3. Combining the two CES pairs, the measured value of γ is 0.984 ± 0.037, which is comparable to the latest published results for Jupiter as a gravitational lens, reported by Fomalont & Kopeikin, i.e., 1.01 ± 0.03.
Highlights
The first observation of light deflection by the Sun (Dyson et al 1920), which tested the theory of general relativity, is praised as the beginning of the “modern era” (Johnson 1983)
We measured the relative positions between two pairs of compact extragalactic sources (CESs), J1925-2219 & J1923-2104 (C1–C2) and J1925-2219 & J1928-2035 (C1–C3) on 2020 October 23–25 and 2021 February 5, respectively, using the Very Long Baseline Array (VLBA) at 15 GHz
Accounting for the deflection angle dominated by Jupiter, as well as the contributions from the Sun, planets other than Earth, the Moon and Ganymede, our theoretical calculations predict that the dynamical ranges of the relative positions across four epochs in R.A. of the C1–C2 pair and C1–C3 pair are 841.2 and 1127.9 μas, respectively
Summary
The first observation of light deflection by the Sun (Dyson et al 1920), which tested the theory of general relativity, is praised as the beginning of the “modern era” (Johnson 1983). Testing general relativity has been a perennial hot issue since and with the accumulation of astrometric data and technological developments, increasingly better accuracy is being achieved. In the coming decades another 3–4 orders of magnitude of improvement in testing relativistic gravity is expected to be achieved, taking advantage of the rapid development of modern technology (Ni 2017). It is essential to test different metric theories of gravity (e.g., Damour & Nordtvedt 1993; Fomalont et al 2009), and this in turn is vital to future ultraprecise and ultrasensitive observatories, because the difference between the predicted deflection angles of the different theories may be comparable to or even smaller than the expected astrometric errors. Measuring deflection angles and testing gravitational theory or its high-order approximations are two indispensable and urgent tasks
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