Fourier Resolved Spectroscopy of the XMM-Newton Observations of MCG -6-30-15

Abstract

We study the Frequency Resolved Spectra of the Seyfert galaxy MCG -6-30-15 obtained during two recent XMM-Newton observations. Splitting the Fourier spectra in soft (<2 keV) and hard (>2 keV) bands, we find that the soft band has a variability amplitude larger than the hard one on time scales longer than 10 ksec, while the opposite is true on time scales shorter than 3 ksec. Both the soft and hard band spectra are well fitted by power laws of different indices. The spectra of the hard band become clearly softer as the Fourier Frequency decreases from 7x10^{-4} Hz to 10^{-5} Hz, while the spectral slope of the soft band power law component is independent of the Fourier frequency. The well known broad Fe Ka feature is absent at all frequency bins; this result implies that this feature is not variable on time scales shorter than ~10^5 sec, in agreement with recent line variability studies. Strong spectral features are also present in the soft X-ray band (at E~0.7), clearly discernible in all Fourier Frequency bins. This fact is consistent with the assumption that they are due to absorption by intervening matter within the source.