Self-lensing flares from black hole binaries II: observing black hole shadows via light-curve tomography

TL;DR

This paper proposes a method to observe black hole shadows in supermassive black hole binaries through light-curve tomography, enabling shadow detection even when direct imaging is not possible.

Contribution

It introduces a novel BH tomography technique using light-curve features caused by self-lensing flares, allowing shadow observation without high-resolution imaging.

Findings

1% of current binary candidates may show detectable shadow features

Ray-tracing models predict distinct light-curve signatures of BH shadows

Method enables shadow extraction from unresolved light-curve data

Abstract

Supermassive black hole (BH) binaries are thought to produce self-lensing flares (SLF) 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 BH shadow from the lensed 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 VLBI.