BASS-XL: X-ray variability properties of unobscured active galactic nuclei
Kawamuro, Taiki; Ricci, Claudio; Bauer, Franz E.; Stern, Daniel; Trakhtenbrot, Benny; Mushotzky, Richard; Harrison, Fiona; Caglar, Turgay; Koss, Michael J.; Oh, Kyuseok; Ricci, Federica; Liu, Tingting; Temple, Matthew J.; Tortosa, Alessia; Arévalo, Patricia; Urry, Claudia Megan; Rojas Lilayu, Alejandra; Powell, Meredith Clark
Chile, Italy, China, United States, Israel, Japan, South Korea
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 $\sigma _{\rm NXS}^2$ 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 $\sigma _{\rm NXS}^2$ 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 $\sigma _{\rm NXS}^2$ 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.