  We report on the first XMM-Newton observation of the highly X-ray variable,
radio-quiet, Narrow-Line Seyfert 1 galaxy IRAS 13224-3809 obtained during the
guaranteed time programme with a 64 ks exposure. The most remarkable spectral
feature is a sharp drop, by a factor ~5, in the spectrum at 8 keV. This is a
similar, but stronger, feature to that which we found in 1H0707-495.
Significant flattening of the hard X-ray spectrum occurs when the source flux
decreases. The flattening of the spectrum can be modelled as an increase in the
column density of the absorbing material and/or its covering fraction. Below ~
1.5 keV the spectrum is dominated by a giant soft X-ray excess, and at around ~
1.2 keV there is a significant absorption feature detected, most probably due
to ionized Fe L absorption. The new X-ray spectral properties detected with
XMM-Newton in IRAS 13224-3809 support a partial covering interpretation, i.e.
the presence of dense material inside the accretion-disc region partially
obscuring the emission from the accretion disc. However, the sharpness of the
feature, if due to photoelectric absorption, is surprising and may require an
alternative explanation. One possibility which does fit the whole spectrum is
that it is dominated by ionized reflection rather than absorption. The unusual
spectral properties detected with XMM-Newton from Narrow-Line Seyfert 1
galaxies increase the known spectral complexity of active galactic nuclei and
should further stimulate a combined theoretical and observational effort to
achieve a better understanding of the physics of the innermost regions of AGN.
