Christopher S. Reynolds
We use the method of Press, Rybicki & Hewitt (1992) to search for time
lags and time leads between different energy bands of the RXTE data for
MCG-6-30-15. We tailor our search in order to probe any reverberation
signatures of the fluorescent iron K 
line that is thought to
arise from the inner regions of the black hole accretion disk. In
essence, an optimal reconstruction algorithm is applied to the continuum
band (2-4keV) light curve which smoothes out noise and interpolates
across the data gaps. The reconstructed continuum band light curve can
then be folded through trial transfer functions in an attempt to find
lags or leads between the continuum band and the iron line band
(5-7keV). We find reduced fractional variability in the line band.
The spectral analysis of Lee et al. (1999) reveals this to be due to a
combination of an apparently constant iron line flux (at least on
timescales of 
), and flux correlated changes in
the photon index. We also find no evidence for iron line reverberation
and exclude reverberation delays in the range 0.5-50ksec. This
extends the conclusions of Lee et al. and suggests that the iron line
flux remains constant on timescales as short as 0.5ksec. The large
black hole mass ( 
) naively suggested by the constancy of the
iron line flux is rejected on other grounds. We suggest that the black
hole in MCG-6-30-15 has a mass of 
and
that changes in the ionization state of the disk may produce the
puzzling spectral variability. Finally, it is found that the 8-15keV
band lags the 2-4keV band by 50-100s. This result is used to
place constraints on the size and geometry of the Comptonizing medium
responsible for the hard X-ray power-law in this AGN.