We report a direct and accurate measurement of the distance to the X-ray binary Cygnus X-1, which contains the first black hole to be discovered. The distance of 1.86 (-0.11,+0.12) kpc was obtained from a trigonometric parallax measurement using the Very Long Baseline Array. The position measurements are also sensitive to the 5.6 d binary orbit and we determine the orbit to be clockwise on the sky. We also measured the proper motion of Cygnus X-1 which, when coupled to the distance and Doppler shift, gives the three-dimensional space motion of the system. When corrected for differential Galactic rotation, the non-circular (peculiar) motion of the binary is only about 21 km/s, indicating that the binary did not experience a large "kick" at formation.
@article{arxiv.1106.3688,
title = {The Trigonometric Parallax of Cygnus X-1},
author = {Mark J. Reid and Jeffrey E. McClintock and Ramesh Narayan and Lijun Gou and Ronald A. Remillard and Jerome A. Orosz},
journal= {arXiv preprint arXiv:1106.3688},
year = {2015}
}
Comments
Paper I of three papers on Cygnus X-1; 13 pages including 3 figures and 2 tables, ApJ in press