MOA-2011-BLG-322Lb: a "second generation survey" microlensing planet
  Global "second-generation" microlensing surveys aim to discover and
characterize extrasolar planets and their frequency, by means of
round-the-clock high-cadence monitoring of a large area of the Galactic bulge,
in a controlled experiment. We report the discovery of a giant planet in
microlensing event MOA-2011-BLG-322. This moderate-magnification event, which
displays a clear anomaly induced by a second lensing mass, was inside the
footprint of our second-generation microlensing survey, involving MOA, OGLE and
the Wise Observatory. The event was observed by the survey groups, without
prompting alerts that could have led to dedicated follow-up observations.
Fitting a microlensing model to the data, we find that the timescale of the
event was t_E=23.2 +/-0.8 days, and the mass ratio between the lens star and
its companion is q=0.028 +/-0.001. Finite-source effects are marginally
detected, and upper limits on them help break some of the degeneracy in the
system parameters. Using a Bayesian analysis that incorporates a Galactic
structure model, we estimate the mass of the lens at 0.39 +0.45/-0.19 M_sun, at
a distance of 7.56 +/-0.91 kpc. Thus, the companion is likely a planet of mass
11.6 +13.4/-5.6 M_J, at a projected separation of 4.3 +1.5/-1.2 AU, rather far
beyond the snow line. This is the first pure-survey planet reported from a
second-generation microlensing survey, and shows that survey data alone can be
sufficient to characterize a planetary model. With the detection of additional
survey-only planets, we will be able to constrain the frequency of extrasolar
planets near their systems' snow lines.
