BASS-XL: X-ray variability properties of unobscured active galactic nuclei

Abstract

We investigate the X-ray variability properties of Seyfert 1 Galaxies belonging to the BAT AGN Spectroscopic Survey (BASS). The sample includes 151 unobscured (NH < 1022 cm-2) AGNs observed with XMM-Newton for a total exposure time of ∼27 ms, representing the deepest variability study done so far with high signal-To-noise XMM-Newton observations, almost doubling the number of observations analysed in previous works. We constrain the relation between the normalized excess variance and the 2-10 keV AGN luminosities, black hole masses, and Eddington ratios. We find a highly significant correlation between and MBH, with a scatter of ∼0.85 dex. For sources with high L2-10 this correlation has a lower normalization, confirming that more luminous (higher mass) AGNs show less variability. We explored the versus MBH relation for the sub-sample of sources with MBH estimated via the 'reverberation mapping' technique, finding a tighter anticorrelation, with a scatter of ∼0.65 dex. We examine how the changes with energy by studying the relation between the variability in the hard (3-10 keV) and the soft (0.2-1 keV)/medium (1-3 keV) energy bands, finding that the spectral components dominating the hard energy band are more variable than the spectral components dominating in softer energy bands, on time-scales shorter than 10 ks.