Fourier-resolved spectroscopy of active galactic nuclei using XMM-Newton data. I. The 3-10 keV band results

We present the results from Fourier-resolved spectroscopy of archival XMM-Newton data of five AGNs, namely, Mrk 766, NGC 3516, NGC 3783, NGC 4051, and Ark 564. This work supplements an earlier study of MCG -6-30-15 and of several Galactic black hole candidate sources. Our results exhibit much larger diversity than for Galactic sources, a fact we attribute to the diversity of their masses. When we take into account this effect and combine our results with those for Cyg X-1, it seems reasonable to conclude that at high frequencies, the slope of the Fourier-resolved spectra in accreting black hole systems decreases with increasing frequency as ∝ f^-0.25, irrespective of whether the system is in its high or low state. This result implies that the flux variations in AGNs are accompanied by complex spectral slope variations as well. We also find that the Fe Kα line in Mrk 766, NGC 3783, and NGC 4051 is variable on timescales of ∼1 day to 1 hr. The iron fluorescence line is absent in the spectra of the highest frequencies, and there is an indication that, just like in Cyg X-1, the equivalent width of the line in the Fourier-resolved AGNs decreases with increasing frequency.