* Astronomy

Title: A possible binary system of a stellar remnant in the high magnification gravitational microlensing event OGLE-2007-BLG-514
Authors: N. Miyake, A. Udalski, T. Sumi, D. P. Bennett, S. Dong, R. A. Street, J. Greenhill, I. A. Bond, A. Gould, M. Kubiak, M. K. Szymanski, G. Pietrzynski, I. Soszynski, K. Ulaczyk, L. Wyrzykowski (The OGLE Collaboration) F. Abe, A. Fukui, K. Furusawa, S. Holderness, Y. Itow, A. Korpela, C. H. Ling, K. Masuda, Y. Matsubara, Y. Muraki, T. Nagayama, K. Ohnishi, N. Rattenbury, To. Saito, T. Sako, D. J. Sullivan, W. L. Sweatman, P. J. Tristram, P. C. M. Yock (The MOA Collaboration) W. Allen, G. W. Christie, D. L. DePoy, B. S. Gaudi, C. Han, C.-U. Lee, J. McCormick, B. Monard, T. Natusch, B.-G. Park, R. W. Pogge (The muFUN Collaboration) A. Allan, M. Bode, D. M. Bramich, N. Clay, M. Dominik, K. D. Horne, N. Kains, C. Mottram, C. Snodgrass, I. Steele, Y. Tsapras (The RoboNet Collaboration) M. D. Albrow, et al. (24 additional authors not shown)

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 ±0.39 kpc and total mass M_L=1.40 ±0.18 solar masses; this leads to the primary and secondary components having masses of M_1 = 1.06 ±0.13 solar masses and M_2 = 0.34 ±0.04 solar masses, 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 M_1 = 0.9_{-0.3}^{+4.6} solar masses and it is at a distance of D_L = 2.6_{-0.9}^{+3.8} kpc. Given the secure mass ratio measurement, the companion mass is therefore M_2 = 0.2_{-0.1}^{+1.2} solar masses. 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.

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