MOA 2003‐BLG‐37: A Bulge Jerk‐Parallax Microlens Degeneracy

Abstract

We analyze the Galactic bulge microlensing event MOA 2003-BLG-37. Although the Einstein timescale is relatively short, t E = 43 days, the light curve displays deviations consistent with parallax effects due to the Earth's accelerated motion. We show that the χ 2 surface has four distinct local minima that are induced by the "jerk-parallax" degeneracy, with pairs of solutions having projected Einstein radii r̃ E = 1.76 and 1.28 AU, respectively. This is the second event displaying such a degeneracy and the first toward the Galactic bulge. For both events, the jerk-parallax formalism accurately describes the offsets between the different solutions, giving hope that when extra solutions exist in future events they can easily be found. However, the morphologies of the χ 2 surfaces for the two events are quite different, implying that much remains to be understood about this degeneracy.