Fourier-Resolved Spectroscopy of the XMM-Newton Observations of MCG -06-30-15

Abstract

We study the frequency-resolved spectra of the Seyfert galaxy MCG -06-30-15 obtained during two recent XMM-Newton observations. Splitting the Fourier spectra in soft (E<~2 keV) and hard (E>~2 keV) bands, we find that the soft band has a variability amplitude larger than the hard one on timescales longer than 10 ks, while the opposite is true on timescales shorter than 3 ks. 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 7×10^-4 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 Kα feature is absent at all frequency bins; this result implies that this feature is not variable on timescales shorter than ~10⁵ s, 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.