The Position of Sgr A$^*$ at the Galactic Center

Abstract

The absolute position of the compact radio source at the dynamical center of the Galaxy, Sgr A$^*$, was known only to an accuracy of $0.2''$ in spite of its accurate location with respect to near-IR stellar sources to within 30 milliarcsecond (mas). To remedy this poor positional accuracy, we have selected 15 high-resolution, high-frequency VLA observations of Sgr A$^*$ carried out in the last 13 years and determined the weighted average position with the average epoch 1992.4 to be at $\alpha$, $\delta$[1950] = $17^{\rm h} 42^{\rm m}$ 29\dsec3076$\pm0.0007$, $-28^\circ 59^\prime 18.484\pm0.014^{\prime\prime}$, or $\alpha$, $\delta $[2000] = $17^{\rm h} 45^{\rm m}$ 40\dsec0383$\pm0.0007$, $-29^\circ 00^\prime 28.069\pm0.014^{\prime\prime}$ which agrees with earlier published values to within the $0.2''$ error bars of the earlier measurements. An accurate absolute position of Sgr A$^*$ can be useful for its identification with sources at other wavelengths, particularly, in soft and hard X-rays with implications for the models of a massive black hole at the Galactic center.