Light Loop Echoes and Blinking Black Holes
Latham Boyle (CITA, Perimeter), Matthew Russo (CITA)

TL;DR
This paper models the 'blinking' effect in light curves caused by multiple light paths near a black hole, especially in face-on configurations, revealing strong signals that could aid black hole observations.
Contribution
It provides detailed calculations of time delays and magnifications for multiple light paths near a black hole, highlighting the detectability of blinking signals in face-on geometries.
Findings
Blinking signals are enhanced in face-on configurations.
Flux contributions from secondary paths can be significant.
The effect is strongest near the innermost stable circular orbit.
Abstract
Radiation emitted near a black hole reaches the observer by multiple paths; and when this radiation varies in time, the time-delays between the various paths generate a "blinking" effect in the observed light curve L(t) or its auto-correlation function xi(T)= <L(t)L(t-T)>. For the particularly important "face-on" configuration (in which the hole is viewed roughly along its spin axis, while the emission comes roughly from its equatorial plane -- e.g. from the inner edge of its accretion disk, or from the violent flash of a nearby/infalling star) we calculate the blinking in detail by computing the time delay Delta t_{j}(r,a) and magnification mu_{j}(r,a) of the jth path (j=1,2,3,...), relative to the primary path (j=0), as a function of the emission radius r and black hole spin 0<a/M<1. The particular geometry and symmetry of the nearly-face-on configuration enhances and "protects" the…
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Taxonomy
TopicsBlack Holes and Theoretical Physics · Cosmology and Gravitation Theories
