An Anomalous Symmetric Flare Observed in the Single-lined Spectroscopic Binary TIC 380907942: Assessing Self-lensing and Alternative Hypotheses

Abstract We report the observation of an anomalous flare in the Transiting Exoplanet Survey Satellite light curve of TIC 380907942 (HD 10443), a known single-lined spectroscopic binary. Archived spectra suggest this binary contains a G0IV star and an unresolved companion with an orbital period of ∼11 yr. We investigate a variety of hypotheses for the observed light-curve feature, including the possibility that TIC 380907942 is a self-lensing binary in which a compact object gravitationally lenses its stellar companion. We rule out the typical sources of self-lensing false positives, perform a joint fit to the system’s light curve and radial velocity data, and discuss future observations needed to confirm the viability of the self-lensing hypothesis. We evaluate the few alternative theories that cannot be excluded at present, including line-of-sight coincidences such as background dwarf novae or active galactic nucleus, and estimate their relative likelihood. If truly a self-lensing binary, TIC 380907942 would possess, by far, the longest orbital period yet observed for such a system.