We analyze the binary gravitational microlensing event OGLE-2017-BLG-1130 (mass ratio q~0.45), the first published case in which the binary anomaly was only detected by the Spitzer Space Telescope. This event provides strong evidence that some binary signals can be missed by observations from the ground alone but detected by Spitzer. We therefore invert the normal procedure, first finding the lens parameters by fitting the space-based data and then measuring the microlensing parallax using ground-based observations. We also show that the normal four-fold space-based degeneracy in the single-lens case can become a weak eight-fold degeneracy in binary-lens events. Although this degeneracy is resolved in event OGLE-2017-BLG-1130, it might persist in other events.
@article{arxiv.1802.09023,
title = {OGLE-2017-BLG-1130: The First Binary Gravitational Microlens Detected From Spitzer Only},
author = {Tianshu Wang and S. Calchi Novati and A. Udalski and A. Gould and Shude Mao and W. Zang and C. Beichman and G. Bryden and S. Carey and B. S. Gaudi and C. B. Henderson and Y. Shvartzvald and J. C. Yee and P. Mroz and R. Poleski and J. Skowron and M. K. Szymanski and I. Soszynski and S. Kozlowski and P. Pietrukowicz and K. Ulaczyk and M. Pawlak and M. D. Albrow and S. -J. Chung and C. Han and K. -H. Hwang and Y. K. Jung and Y. -H. Ryu and I. -G. Shin and W. Zhu and S. -M. Cha and D. -J. Kim and H. -W. Kim and S. -L. Kim and C. -U. Lee and D. -J. Lee and Y. Lee and B. -G. Park and R. W. Pogge},
journal= {arXiv preprint arXiv:1802.09023},
year = {2018}
}