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

<jats:title>Abstract</jats:title> <jats:p>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<jats:italic>σ</jats:italic>. The two-planet model indicates that the first anomaly was caused by planet “b” with a mass ratio of <jats:inline-formula> <jats:tex-math> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ajaabd7aieqn1.gif" xlink:type="simple"/> </jats:inline-formula> and projected separation in units of the Einstein radius, <jats:italic>s</jats:italic> = 0.753 ± 0.004. The second anomaly reveals planet “c” with a mass ratio of <jats:inline-formula> <jats:tex-math> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ajaabd7aieqn2.gif" xlink:type="simple"/> </jats:inline-formula> with Δ<jats:italic>χ</jats:italic> <jats:sup>2</jats:sup> ∼ 170 compared to the single-planet model. Its separation has two degenerated solutions: the separation of planet c is <jats:italic>s</jats:italic> <jats:sub>2</jats:sub> = 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 <jats:inline-formula> <jats:tex-math> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ajaabd7aieqn3.gif" xlink:type="simple"/> </jats:inline-formula> and <jats:inline-formula> <jats:tex-math> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ajaabd7aieqn4.gif" xlink:type="simple"/> </jats:inline-formula>, respectively, and they orbit a late-type star with a mass of <jats:inline-formula> <jats:tex-math> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ajaabd7aieqn5.gif" xlink:type="simple"/> </jats:inline-formula> located at <jats:inline-formula> <jats:tex-math> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ajaabd7aieqn6.gif" xlink:type="simple"/> </jats:inline-formula> from us. The projected distances between the host and planets are <jats:inline-formula> <jats:tex-math> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ajaabd7aieqn7.gif" xlink:type="simple"/> </jats:inline-formula> for planet b and <jats:inline-formula> <jats:tex-math> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ajaabd7aieqn8.gif" xlink:type="simple"/> </jats:inline-formula> and <jats:inline-formula> <jats:tex-math> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ajaabd7aieqn9.gif" xlink:type="simple"/> </jats:inline-formula> 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 <jats:italic>μ</jats:italic>FUN detection efficiency. It is estimated that 6% ± 2% of stars host two cold giant planets.</jats:p>