First Resolution of Microlensed Images

• Published in: The Astrophysical journal 2019-01, Vol.871 (1), p.70
• Main Authors: Dong, Subo, Mérand, A., Delplancke-Ströbele, F., Gould, Andrew, Chen, Ping, Post, R., Kochanek, C. S., Stanek, K. Z., Christie, G. W., Mutel, Robert, Natusch, T., Holoien, T. W.-S., Prieto, J. L., Shappee, B. J., Thompson, Todd A.
• Format: Article
• Language: English
• Subjects: Astrophysics; Gravitation; Interferometers; Lenses; Parallax; Separation; Very Large Telescope
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/aaeffb

We employ Very Large Telescope Interferometer GRAVITY to resolve, for the first time, the two images generated by a gravitational microlens. The measurements of the image separation mas, and hence the Einstein radius θ E  = 1.87 ± 0.03 mas, are precise. This demonstrates the robustness of the method, provided that the source is bright enough for GRAVITY ( K ≲ 10.5) and the image separation is of order of or larger than the fringe spacing. When θ E  is combined with a measurement of the “microlens parallax” , the two will together yield the lens mass and lens–source relative parallax and proper motion. Because the source parallax and proper motion are well measured by Gaia , this means that the lens characteristics will be fully determined, whether or not it proves to be luminous. This method can be a powerful probe of dark, isolated objects, which are otherwise quite difficult to identify, much less characterize. Our measurement contradicts Einstein’s prediction that “the luminous circle [i.e., microlensed image] cannot be distinguished” from a star.