Studying Microlensing Events from New Horizons

Having successfully completed its main mission, New Horizons could now become a unique observing platform for a wider range of astrophysics. In this paper, we explore the theory and practicalities of using the LORRI imager to observe microlensing events in the Galactic bulge. Simultaneous observations from both Earth and New Horizons could be used to measure the properties of stellar remnant lenses such as the predicted—but so far rarely detected—population of intermediate-mass black holes. While this technique cannot be applied for stellar lenses, it is possible that a single source star could be lensed by the same foreground object in two sequential microlensing events, and we explore the opportunities that this novel strategy provides for understanding the nature of the lens. With any microlensing event, two independent mass-distance relations are required to determine the physical properties of the lens. This is most commonly achieved by combining measurements of the parallax with those of the effects of the finite extent of the source star on the event light curve. We explore whether New Horizons’ trajectory could be used to constrain event parallax. As with any observatory, there are practical considerations that shape viable observing strategies.