Identify the origin of a single observed spectral modulation frequency

Determine whether a single detected periodic spectral variation in a supermassive-black-hole binary should be attributed to the minidisks or to the circumbinary disk.

Background

The paper predicts periodic modulation of iron and oxygen emission features from the orbiting inner edge of the circumbinary disk, while previous work has proposed periodic Doppler shifts of iron-line components produced by the two minidisks. These mechanisms can generate distinct characteristic frequencies, but an observation may reveal only one periodicity.

The authors state that a Fourier analysis showing two frequencies separated by a factor of roughly 0.1–0.2 would indicate a binary, whereas a single frequency would not by itself establish whether the signal originates in the minidisks or in the circumbinary disk. This attribution therefore remains unresolved in the single-frequency case.