Negative X-ray reverberation time delays from MCG-6-30-15 and Mrk 766

We present an X-ray time lag analysis, as a function of Fourier frequency, for MCG-6-30-15 and Mrk 766 using long-term XMM-Newton light curves in the 0.5-1.5 and the 2-4 keV energy bands, together with some physical modelling of the corresponding time lag spectra. Both the time lag spectra of MCG-6-30-15 and Mrk 766 show negative values (i.e. soft band variations lag behind the corresponding hard band variations) at high frequencies, around 10^-3 Hz, similar to those previously observed from 1H 0707-495. The remarkable morphological resemblance between the time lag spectra of MCG-6-30-15 and Mrk 766 indicate that the physical processes responsible for the observed soft time delays are very similar in the two sources, favouring a reflection scenario from material situated very nearby to the central black hole. ^a The effective observing time, i.e. light curve duration, after the reduction of the raw data. ^b For the pn, MOS 1 and MOS 2, respectively. sw: small window, lw: large window and fw: fast uncompressed. ^c The mean count rate and the standard deviation of the light curve in the 0.5-4 keV energy band.