X-ray light curves of active galactic nuclei are phase incoherent

The authors compute the Fourier phase spectra for the light curves of five low-luminosity active galactic nuclei observed by EXOSAT. There is no statistically significant phase coherence in any of them. This statement is equivalent, subject to a technical caveat, to a demonstration that their fluctuation statistics are Gaussian. Models in which the X-ray output is controlled wholly by a unitary process undergoing a nonlinear limit cycle are therefore ruled out, while models with either a large number of randomly excited independent oscillation modes or nonlinearly interacting spatially dependent oscillations are favored. The authors also demonstrate how the degree of phase coherence in light curve fluctuations influences the application of causality bounds on internal length scales

Duke Scholars

Author Jeffrey L. Krolik Electrical and Computer Engineering