Existence of decade-stable clocks in blazars

Determine whether any gamma-ray blazar hosts a clock-like modulation that remains stable over decades, extending beyond the approximately 18-year observational baseline analyzed in the study.

Background

The study develops a morphology-based analysis of year-scale gamma-ray variability in blazars, measuring coherence, persistence, period drift, and cycle-to-cycle volatility over an approximately 18-year Fermi-LAT baseline. Two sources exhibit persistent, coherent, and apparently stationary modulation, but the analysis finds that neither source is individually established as periodic and that red noise can reproduce Rank I behavior at a non-negligible rate.

The authors emphasize that stable morphology is not uniquely diagnostic of a binary black-hole origin: long-lived precession or other mechanisms could produce an indistinguishable signal over the available baseline. A substantially longer time series would be needed to test whether any candidate maintains its period over decades and to distinguish competing physical interpretations.