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 \pm 0.8 days , and the mass ratio between the lens star and its companion is q = 0.028 \pm 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 _ { \odot } , at a distance of 7.56 \pm 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 .