Self-Lensing flares from black hole binaries: Observing black hole shadows via light curve tomography

Supermassive black hole (BH) binaries are thought to produce self-lensing flares (SLFs) when the two BHs are aligned with the line of sight. If the binary orbit is observed nearly edge-on, we find a distinct feature in the light curve imprinted by the relativistic shadow around the background (“source”) BH. We study this feature by ray tracing in a binary model and predict that 1% of the current binary candidates could show this feature. Our BH tomography method proposed here could make it possible to extract BH shadows that are spatially unresolvable by high-resolution very long base line interferometry (VLBI).