Extreme lensing induces spectro-temporal correlations in black-hole signals

Understand

Rapid progress in electromagnetic black hole observation presents a theoretical challenge: how can the universal signatures of extreme gravitational lensing be distilled from stochastic astrophysical signals? With this motivation, the two-point correlation function of specific intensity fluctuations across image positions, times, and frequencies is here considered.

• The contribution of strongly deflected light rays, those which make up the photon ring, is analytically computed for a Kerr black hole illuminated by a simple geometric-statistical emission model.
• We subsequently integrate over the image to yield a spectro-temporal correlation function which is relevant for unresolved sources.
• Finally, some observational aspects are discussed and a preliminary assessment of detectability with current and upcoming missions is provided.