CAIXA: a catalogue of AGN in the XMM-Newton archive III. Excess Variance Analysis
Gabriele Ponti, Iossif Papadakis, Stefano Bianchi, Matteo Guainazzi,, Giorgio Matt, Phil Uttley, Fonseca Bonilla, Nuria

TL;DR
This study analyzes X-ray variability in 161 radio-quiet, unobscured AGN using excess variance, revealing strong correlations with black hole mass and spectral index, and demonstrating variability as a precise MBH measurement tool.
Contribution
It provides the largest systematic excess variance analysis of AGN X-ray variability, establishing its strong correlation with MBH and refining understanding of variability dependencies.
Findings
Excess variance correlates tightly with MBH (~0.7 dex)
Reverberation-mapped AGN show even smaller scatter (~0.45 dex)
Variability properties are consistent across AGN types once scaled for MBH and accretion rate
Abstract
We report on the results of the first XMM systematic "excess variance" study of all the radio quiet, X-ray un-obscured AGN. The entire sample consist of 161 sources observed by XMM for more than 10 ks in pointed observations which is the largest sample used so far to study AGN X-ray variability on time scales less than a day. We compute the excess variance for all AGN, on different time-scales (10, 20, 40 and 80 ks) and in different energy bands (0.3-0.7, 0.7-2 and 2-10 keV). We observe a highly significant and tight (~0.7 dex) correlation between excess variance and MBH. The subsample of reverberation mapped AGN shows an even smaller scatter (~0.45 dex) comparable to the one induced by the MBH uncertainties. This implies that X-ray variability can be used as an accurate tool to measure MBH and this method is more accurate than the ones based on single epoch optical spectra. The excess…
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Taxonomy
TopicsAstrophysical Phenomena and Observations · Galaxies: Formation, Evolution, Phenomena · Pulsars and Gravitational Waves Research
