Observatory Microlensing and Binary Self Lensing with Roman and with Rubin
Wide-Field Science – Regular
Rosanne Di Stefano / Harvard-Smithsonian Center for Astrophysics, PI
One of the primary goals of the Nancy Grace Roman Space Telescope mission is to establish the population properties of planetary systems in the Galactic Bulge. Its Galactic Bulge Time Domain Survey will be keenly sensitive to microlensing events. With its 15-minute cadence, it is particularly well suited to discover short events that could be free-floating planets, and also the short-term subtle deviations in a stellar-lensing light curve that are caused by planets. Predictions have been made that Roman will discover ~1400 planets via microlensing.
The Rubin Observatory’s Large Survey of Space and Time (LSST) is presently slated to cover the Roman field. It will start observations roughly a year earlier, observe the field in between Roman’s 72-day observation intervals, and continue for several years after Roman concludes. Our team, experts in microlensing and members of the Rubin microlensing group, proposes work that will use the Roman/Rubin Synergy to enable Roman to achieve its bold microlensing goals.
For long events, whether caused by black hole lenses or slow-moving stars, Rubin can play a crucial role in making sure we identify lensing events that do not start and complete within Roman’s observing window. We have been deeply engaged in developing event detection within LSST data, and will be working to identify the roughly 1200 Rubin-detectable events that are expected each year in the 2 square degree Roman field. Many Rubin-detected events that can be detected by Roman, even near baseline, will still be active when Roman starts observations. This applies not only to black-hole lenses. In fact, the events that can be detected by both observatories will be dominated by events with durations of weeks or months.
To increase the numbers of lensing events Roman will identify, and to increase the efficiency for the extraction of correct system parameters, we have devised a two-part plan.
First, we will conduct a sequence of light curve simulations in which we use, sequentially, a variety of Roman and Rubin sampling strategies in the Roman field. Our analyses of the simulated data will help us to identify optimal observing strategies, and should shape the approach both observatories take in the Roman Bulge field.
Second, we will create a Roman Input Microlensing Catalog for the Galactic Bulge. The entries in the catalog will be the event coordinates and the full LSST-multi-band light curves for each lensing event candidate. We will also create a complementary catalog of microlensing imposters–those events that could be easily confused with microlensing events, but which we have found to have other natures. With these catalogs in hand (or rather, downloaded from IPAC), Roman will start observations knowing the locations and prior histories of, potentially, hundreds of events. This will increase Roman’s early science return.
The science return will also be significantly increased by another aspect of the Roman/Rubin Synergy: the complementarity of their spectral coverage. Rubin’s mulitband (up to 6) coverage will provide spectral information about the lensed source and other objects along the line of sight.
From a physical perspective, the importance of this work is not simply an increase in the number of events Roman discovers. Our work will play crucial roles in allowing Roman to correctly characterize the events and, eventually, the full population responsible for planetary microlensing in the Bulge. If our work conducted under the aegis of this program is successful, as we expect it to be, we will take advantage of future funding opportunities to transform the catalog into a dynamic resource that is continuously updated with the combination of Roman and Rubin microlensing data.
Our team is uniquely qualified to conduct this research, which should be started as soon as possible if Roman is to derive the full scientific advantage of the Roman/Rubin microlensing synergy.