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 stmcture 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 + or - 0.007 and a projected separation of s = 0.072 + or - 0.0001 in units of the Einstein radius. The parallaxi parameters allow us to determine the lens distance D sub(L) = 3.11 + or - 0.39 kpc and total mass M sub(L) = 1.40 + or - 0.18M[middot in circle] and M sub(2) = 0.34 + or - 0.04 M[middot in circle], 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 thc source around a companion) and parallax (q = 0.270 + or - 0.0005, s = 0.083 + or - 0,001). The primary component of the binary lens is relatively massive, with M sub(1) = 0.9 super(+4.6) sub(-0.3) M[middot in circle] and it is at a distance of D sub(L) = 2.6 super(+3.8) sub(-0.9) kpc. Given the secure mass ratio measurement, the companion mass is therefore M sub(2) = 0.2 super(+1.2) sub(-0.1) M[middot in circle]. The xallarap model implies that the primary lens is likely a stellar remniant, such as a white dwarf, a neutron star, or a black hole.