Ogle-2018-blg-0677lb: A super earth near the galactic bulge

We report the analysis of the microlensing event OGLE-2018-BLG-0677. A small feature in the light curve of the event leads to the discovery that the lens is a star-planet system. Although there are two degenerate solutions that could not be distinguished for this event, both lead to a similar planet-host mass ratio. We perform a Bayesian analysis based on a Galactic model to obtain the properties of the system and find that the planet corresponds to a super-Earth/sub-Neptune with a mass $M_{$\mathrm{p}\mathrm{l}\mathrm{a}\mathrm{n}\mathrm{e}\mathrm{t}$} = {3.96}^{+5.88}{-2.66}${\mathrm{M}}_{\oplus }$$\mathrm{.}Thehoststarhasamass$ M{$\mathrm{h}\mathrm{o}\mathrm{s}\mathrm{t}$} = {0.12}^{+0.14}_{-0.08}${\mathrm{M}}_{\odot }$$. The projected separation for the inner and outer solutions are ${0.63}_{-0.17}^{+0.20}$~AU and ${0.72}_{-0.19}^{+0.23}$~AU respectively. At $\Delta\chi^2=\chi^2({\rm 1L1S})-\chi^2({\rm 2L1S})=46$,thisisbyfarthelowest$\Delta\chi^2$ for any securely-detected microlensing planet to date, a feature that is closely connected to the fact that it is detected primarily via a “dip” rather than a “bump”.