Relative Magnification Factor of Point Sources on Accretion Disks

TL;DR

This paper introduces the relative magnification factor to analyze point sources on accretion disks near black holes, revealing how source motion affects lensing and can probe accretion flow dynamics.

Contribution

It presents a new framework for understanding how source motion influences gravitational lensing signatures on accretion disks.

Findings

Corotating sources show significant distortions in magnification distribution.

Source motion modulates the caustic structure of lensing.

Magnification patterns encode signatures of accretion flow kinematics.

Abstract

With the Event Horizon Telescope and future Very Long Baseline Interferometry arrays poised to image supermassive black holes, there is an urgent need to understand dynamic aspects of small-scale structure near the supermassive black hole. In this study, we introduce the relative magnification factor to characterize point sources distributed on the surface of the accretion disk near a black hole. We investigate the influence of source motion on this factor, comparing static sources with those corotating with the disk. In contrast to the static case, which can be well-understood in the standard framework of gravitational lensing, corotating sources exhibit significant distortions in the distribution of the magnification factor on both the image and source planes, indicating that the caustic structure is substantially modulated by source motion. This magnification factor pattern encodes signatures of the kinematics of accretion flow when the time-delayed images are incorporated. This potentially offers a novel probe for investigating the interplay between spacetime geometry and properties of accretion flow.