Influence of the Galactic gravitational field on the positional accuracy of extragalactic sources. II Observational appearances and detectability

TL;DR

This paper explores the potential to detect the influence of Galactic gravitational fluctuations on the apparent positions of distant extragalactic sources using high-precision radio interferometry, proposing observational strategies and analyzing detectability thresholds.

Contribution

It introduces a method to observe the jitter effect caused by Galactic gravitational field fluctuations and assesses the observational requirements for detection with current and future interferometers.

Findings

Detection of positional jitter is feasible at 10 μas accuracy over ~2 years.

Current interferometers can detect this effect at 2σ level over 10 years.

Improving accuracy to ~20 μas enhances detection confidence to 3σ over the same period.

Abstract

We consider a possibility of detecting the jitter effect of apparent celestial positions of distant sources due to local fluctuations of the Galaxy gravitational field. It is proposed to observe two samples of extragalactic sources (target and control) in different sky directions using the high-precision radio interferometry. It is shown that on a scale of ~2 years, it is possible to detect a systematic increase in the standard deviation of measured arc lengths of pairs of target sources compared to the control ones at the $3\sigma$-level if the accuracy of differential astrometric observations is around 10 $\mu$as. For the current state-of-the-art accuracy of 30 $\mu$as achieved at the KVN or VERA interferometers, which have shorter baselines in comparison with VLBI, the target and control samples will differ only at the 2$\sigma$-level on the scale of 10 years. To achieve the $3\sigma$-level on this time interval, it is necessary to improve the accuracy up to ~20 $\mu$as. Other possible effects that can also affect the arc length measurements between two sources are discussed, and an observational strategy to minimize them is suggested.