The universal shape of the X-ray variability power spectrum of AGN up to $z\sim 3$

Abstract

We study the ensemble X-ray variability properties of Active Galactic Nuclei (AGN) over a large range of timescales (20 ks $\le T\le$ 14 yrs), redshift ($0\le z\lesssim 3$), luminosities ($10^{40}$ erg s${}^{-1}\le L_X\le 10^{46}$ erg s${}^{-1}$) and black hole (BH) masses ($10^6\le$M${}_{\odot }\le 10^9$). We propose the use of the variance-frequency diagram, as a viable alternative to the study of the power spectral density (PSD), which is not yet accessible for distant, faint and/or sparsely sampled AGN. We show that the data collected from archival observations and previous literature studies are fully consistent with a universal PSD form which does not show any evidence for systematic evolution of shape or amplitude with redshift or luminosity, even if there may be differences between individual AGN at a given redshift or luminosity. We find new evidence that the PSD bend frequency depends on BH mass and, possibly, on accretion rate. We finally discuss the implications for current and future AGN population and cosmological studies.

In press on Astronomy and Astrophysics

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• Continuum optical-UV and X-ray variability of AGN: current results and future challenges
• The SRG/eROSITA All-Sky Survey: X-ray beacons at late cosmic dawn
• The X-ray variability of AGN: power-spectrum and variance analysis of the Swift/BAT light curves
• Characterising X-ray variability in light curves with complex sampling patterns: application to the eROSITA south ecliptic pole survey
• Amoeba: An AGN Model of Optical Emissions Beyond steady-state Accretion discs
• Searching for supermassive black holes binaries within SRG/eROSITA-De I: Properties of the X-ray selected candidates
• The ensemble broad-frequency power spectrum of Stripe-82 quasars from multiple surveys