Multiple Emission States in Active Galactic Nuclei

TL;DR

This study investigates the emission variability of active galactic nuclei (AGN) by analyzing simulated lightcurves, revealing that multi-modal flux distributions suggest complex emission mechanisms beyond simple stochastic processes.

Contribution

It demonstrates that AGN emission cannot be fully explained by uniform stochastic models, indicating multiple activity states or emission regions.

Findings

Flux distributions are Gaussian for shallow power spectra slopes (beta<1)

Flux distributions become multi-modal for steeper slopes (beta>1)

Results challenge the assumption of uniform stochastic emission in AGN

Abstract

We present a test of the emission statistics of active galactic nuclei (AGN), probing the connection between red-noise temporal power spectra and multi-modal flux distributions known from observations. We simulate AGN lightcurves under the assumption of uniform stochastic emission processes for different power-law indices of their power spectra. For sufficiently shallow slopes (power-law indices beta < 1), the flux distributions (histograms) of the resulting lightcurves are approximately Gaussian. For indices corresponding to steeper slopes (beta > 1), the flux distributions become multi-modal. This finding disagrees systematically with results of recent mm/radio observations. Accordingly, we conclude that the emission from AGN does not necessarily originate from uniform stochastic processes even if their power spectra suggest this. Possible mechanisms are transitions between different activity states and/or the presence of multiple, spatially disconnected, emission regions.