A Milliarcsecond-accurate Position for Sagittarius A*

TL;DR

This paper reports highly precise astrometric measurements of Sagittarius A*'s position and proper motion, significantly improving the accuracy of its celestial coordinates and motion estimates using VLBA observations.

Contribution

The study provides milliarcsecond-accurate absolute position and proper motion of Sgr A* based on multi-epoch VLBA phase-referencing observations, refining previous measurements.

Findings

Absolute position of Sgr A* determined with submilliarcsecond accuracy.

Proper motion of Sgr A* measured with high precision.

Updated celestial coordinates and motion vectors for Sgr A*.

Abstract

The absolute position of Sgr A*, the compact radio source at the center of the Milky Way, had been uncertain by several tens of milliarcseconds. Here we report improved astrometric measurements of the absolute position and proper motion of Sgr A*. Three epochs of phase-referencing observations were conducted with the Very Long Baseline Array for Sgr A* at 22 and 43 GHz in 2019 and 2020. Using extragalactic radio sources with submilliarcsecond-accurate positions as reference, we determined the absolute position of Sgr A* at a reference epoch 2020.0 to be at $\alpha$(J2000) = $17^{\rm h} 45^{\rm m}40.^{\rm s}032863~\pm~0.^{\rm s}000016$ and $\delta$(J2000) = $-29^{\circ} 00^{\prime} 28.^{''}24260~\pm~0.^{''}00047$, with an updated proper motion $-3.152~\pm~0.011$ and $-5.586~\pm~0.006$ mas yr$^{-1}$ in the easterly and northerly directions, respectively.