A Likely Detection of a Two-planet System in a Low-magnification Microlensing Event

We report on the analysis of a microlensing event, OGLE-2014-BLG-1722, that showed two distinct short-term anomalies. The best-fit model to the observed light curves shows that the two anomalies are explained with two planetary mass ratio companions to the primary lens. Although a binary-source model is also able to explain the second anomaly, it is marginally ruled out by 3.1 sigma. The two-planet model indicates that the first anomaly was caused by planet "b" with a mass ratio of q = (4.5(-0.6)(+0.7)) x 10(-4) and projected separation in units of the Einstein radius, s = 0.753 +/- 0.004. The second anomaly reveals planet "c" with a mass ratio of q(2) = (7.0(-1.7)(+2.3)) x 10(-4) with Delta chi(2) similar to 170 compared to the single-planet model. Its separation has two degenerated solutions: the separation of planet c is s(2) = 0.84 +/- 0.03 and 1.37 +/- 0.04 for the close and wide models, respectively. Unfortunately, this event does not show clear finite-source and microlensing parallax effects; thus, we estimated the physical parameters of the lens system from Bayesian analysis. This gives the masses of planets b and c as m(b) = 56(-33)(+51) and m(c) =85(-51)(+86) M-circle plus, respectively, and they orbit a late-type star with a mass of M-host = 0.40(-0.24)(+0.36) M-circle dot located at D-L 6.4(-1.8)(+1.3) kpc from us. The projected distances between the host and planets are r(perpendicular to),(b) = 1.5 +/- 0.6 au for planet b and r(perpendicular to),(c) = 1.7(-0.6)(+0.7) au and r(perpendicular to),(c) = 2.7(-1.0)(+1.1) au for the close and wide models of planet c. If the two-planet model is true, then this is the third multiple-planet system detected using the microlensing method and the first multiple-planet system detected in low-magnification events, which are dominant in the microlensing survey data. The occurrence rate of multiple cold gas giant systems is estimated using the two such detections and a simple extrapolation of the survey sensitivity of the 6 yr MOA microlensing survey combined with the 4 yr mu FUN detection efficiency. It is estimated that 6% +/- 2% of stars host two cold giant planets.