The rhythm of Fairall 9 -- I: Observing the spectral variability with
  XMM-Newton and NuSTAR
  We present a multi-epoch X-ray spectral analysis of the Seyfert 1 galaxy
Fairall 9. Our analysis shows that Fairall 9 displays unique spectral
variability in that its ratio residuals to a simple absorbed power law in the
0.5-10 keV band remain constant with time in spite of large variations in flux.
This behavior implies an unchanging source geometry and the same emission
processes continuously at work at the timescale probed. With the constraints
from NuSTAR on the broad-band spectral shape, it is clear that the soft excess
in this source is a superposition of two different processes, one being blurred
ionized reflection in the innermost parts of the accretion disk, and the other
a continuum component such as spatially distinct Comptonizing region.
Alternatively, a more complex primary Comptonization component together with
blurred ionized reflection could be responsible.
