A possible binary system of a stellar remnant in the high-magnification gravitational microlensing event OGLE-2007-BLG-514

We report the extremely high-magnification (A > 1000) binary microlensing event OGLE-2007-BLG-514. We obtained good coverage around the double peak structure in the light curve via follow-up observations from different observatories. The binary lens model that includes the effects of parallax (known orbital motion of the Earth) and orbital motion of the lens yields a binary lens mass ratio of q = 0.321 ± 0.007 and a projected separation of s = 0.072 ± 0.001 in units of the Einstein radius. The parallax parameters allow us to determine the lens distance D_L = 3.11 ± 0.39kpc and total mass M_L = 1.40 ± 0.18 M⊙; this leads to the primary and secondary components having masses of M₁ = 1.06 ± 0.13 M⊙ and M₂ = 0.34 ± 0.04 M⊙, respectively. The parallax model indicates that the binary lens system is likely constructed by the main-sequence stars. On the other hand, we used a Bayesian analysis to estimate probability distributions by the model that includes the effects of xallarap (possible orbital motion of the source around a companion) and parallax (q = 0.270 ± 0.005, s = 0.083 ± 0.001). The primary component of the binary lens is relatively massive, with M₁ = 0.9+4.6-0.3 M⊙ and it is at a distance of D_L = 2.6+3.8-0.9 kpc. Given the secure mass ratio measurement, the companion mass is therefore M₂ = 0.2+1.2-0.1 M⊙. The xallarap model implies that the primary lens is likely a stellar remnant, such as a white dwarf, a neutron star, or a black hole.