MOA-2019-BLG-008Lb: A New Microlensing Detection of an Object at the Planet/Brown Dwarf Boundary

We report on the observations, analysis and interpretation of the microlensing event MOA-2019-BLG-008. The observed anomaly in the photometric light curve is best described through a binary lens model. In this model, the source did not cross caustics and no finite-source effects were observed. Therefore, the angular Einstein ring radius theta (E) cannot be measured from the light curve alone. However, the large event duration, t (E) similar to 80 days, allows a precise measurement of the microlensing parallax pi (E). In addition to the constraints on the angular radius theta (*) and the apparent brightness I ( s ) of the source, we employ the Besancon and GalMod galactic models to estimate the physical properties of the lens. We find excellent agreement between the predictions of the two galactic models: the companion is likely a resident of the brown dwarf desert with a mass M ( p ) similar to 30 M (Jup), and the host is a main-sequence dwarf star. The lens lies along the line of sight to the Galactic bulge, at a distance of <= 4 kpc. We estimate that in about 10 yr the lens and source will be separated by similar to 55 mas, and it will be possible to confirm the exact nature of the lensing system by using high-resolution imaging from ground- or space-based observatories.