KMT-2018-BLG-1743: planetary microlensing event occurring on two source stars

Aims. We present the analysis of the microlensing event KMT-2018-BLG-1743. The analysis was conducted as a part of the project, in which previous lensing events detected in and before the 2019 season by the KMTNet survey were reinvestigated with the aim of finding solutions of anomalous events with no suggested plausible models. Methods. The light curve of the event, with a peak magnification A peak ~ 800, exhibits two anomaly features, one around the peak and the other on the falling side of the light curve. An interpretation with a binary lens and a single source (2L1S) cannot describe the anomalies. By conducting additional modeling that includes an extra lens (3L1S) or an extra source (2L2S) relative to a 2L1S interpretation, we find that 2L2S interpretations with a planetary lens system and a binary source best explain the observed light curve with Δ χ 2 ~ 188 and ~91 over the 2L1S and 3L1S solutions, respectively. Assuming that these Δ χ 2 values are adequate for distinguishing the models, the event is the fourth 2L2S event and the second 2L2S planetary event. The 2L2S interpretations are subject to a degeneracy, resulting in two solutions with s > 1.0 (wide solution) and s < 1.0 (close solution). Results. The masses of the lens components and the distance to the lens are ( M host / M ⊙ , M planet / M J , D L /kpc)~(0.19 −0.111 +0.27 ,0.25 −0.14 +0.34 ,6.48 −1.03 +0.94 ) and ~(0.42 −0.25 +0.34 ,1.61 −0.97 +1.30 ,6.04 −1.27 +0.93 ) according to the wide and close solutions, respectively. The source is a binary composed of an early G dwarf and a mid M dwarf. The values of the relative lens-source proper motion expected from the two degenerate solutions, μ wide ~ 2.3 mas yr −1 and μ close ~ 4.1 mas yr −1 , are substantially different, and thus the degeneracy can be broken by resolving the lens and source from future high-resolution imaging observations.