Trigonometric parallax and proper motion of Sagittarius A* measured by VERA using the new broad-band back-end system OCTAVE-DAS

Abstract

We successfully measured the trigonometric parallax of Sagittarius A* (Sgr A*) to be $117\pm 17$ micro-arcseconds ($\hat{I}¼$as) using the VLBI Exploration of Radio Astrometry (VERA) with the newly developed broad-band signal-processing system named OCTAVE-DAS. The measured parallax corresponds to a Galactocentric distance at the Sun of $R_0=8.5_{-1.1}^{+1.5}$ kpc. By combining the astrometric results with VERA and the Very Long Baseline Array (VLBA) over a monitoring period of 25 years, the proper motion of Sgr A* is obtained to be $(\hat{I}{¼}_{\hat{I}}\pm ,\hat{I}{¼}_{\hat{I}}´)=(-3.133\pm 0.003,-5.575\pm 0.005)$ mas yr${}^{-1}$ in equatorial coordinates, corresponding to $(\hat{I}{¼}_l,\hat{I}{¼}_b)=(-6.391\pm 0.005,-0.230\pm 0.004)$ mas yr${}^{-1}$ in Galactic coordinates. This gives an angular orbital velocity of the Sun of $\hat{I}{\text{c◯}}_{\odot }=30.30\pm 0.02$ km s${}^{-1}$ kpc${}^{-1}$. We find upper limits to the core wander, $\hat{I}”\hat{I}¸<0.20$ mas (1.6 AU), peculiar motion, $\hat{I}”\hat{I}¼<0.10$ mas yr${}^{-1}$ (3.7 km s${}^{-1}$), and acceleration, $a<2.6$ $\hat{I}¼$as yr${}^{-2}$ (0.10 km s${}^{-1}$ yr${}^{-1}$) for Sgr A*. Thus, we obtained upper mass limits of $\approx$ 3 $\times$ 10${}^4$$M_{\odot }$ and $\approx$ 3 $\times$ 10${}^3$$M_{\odot }$ for the supposed intermediate-mass black holes at 0.1 and 0.01 pc from the Galactic center, respectively.

15 pages, 9 figures, accepted for publication in the Publications of the Astronomical Society of Japan