Title: The First Planetary Microlensing Event with Two Microlensed Source Stars,
Abstract: We present the analysis of microlensing event MOA-2010-BLG-117, and show that
the light curve can only be explained by the gravitational lensing of a binary
source star system by a star with a Jupiter mass ratio planet. It was necessary
to modify standard microlensing modeling methods to find the correct light
curve solution for this binary-source, binary-lens event. We are able to
measure a strong microlensing parallax signal, which yields the masses of the
host star, $M_* = 0.58\pm 0.11 M_\odot$, and planet $m_p = 0.54\pm 0.10 M_{\rm
Jup}$ at a projected star-planet separation of $a_\perp = 2.42\pm 0.26\,$AU,
corresponding to a semi-major axis of $a = 2.9{+1.6\atop -0.6}\,$AU. Thus, the
system resembles a half-scale model of the Sun-Jupiter system with a
half-Jupiter mass planet orbiting a half-solar mass star at very roughly half
of Jupiter's orbital distance from the Sun. The source stars are slightly
evolved, and by requiring them to lie on the same isochrone, we can constrain
the source to lie in the near side of the bulge at a distance of $D_S = 6.9 \pm
0.7\,$kpc, which implies a distance to the planetary lens system of $D_L =
3.5\pm 0.4\,$kpc. The ability to model unusual planetary microlensing events,
like this one, will be necessary to extract precise statistical information
from the planned large exoplanet microlensing surveys, such as the WFIRST
microlensing survey.