  We report the results of an X-ray observing campaign on the massive, evolved
star Eta Carinae, concentrating on the 2003 X-ray minimum as seen by the
XMM-Newton observatory. These are the first spatially-resolved X-ray monitoring
observations of the stellar X-ray spectrum during the minimum. The hard X-ray
emission, believed to be associated with the collision of Eta Carinae's wind
with the wind from a massive companion star, varied strongly in flux on
timescales of days, but not significantly on timescales of hours. The lowest
X-ray flux in the 2-10 keV band seen by XMM-Newton was only 0.7% of the maximum
seen by RXTE just before the X-ray minimum. The slope of the X-ray continuum
above 5 keV did not vary in any observation, which suggests that the electron
temperature of the hottest plasma associated with the stellar source did not
vary significantly at any phase. Through the minimum, the absorption to the
stellar source increased by a factor of 5-10 to NH ~3-4E23 cm-2. The thermal Fe
XXV emission line showed significant excesses on both the red and blue sides of
the line outside the minimum and exhibited an extreme red excess during the
minimum. The Fe fluorescence line at 6.4 keV increased in equivalent width from
100 eV outside the minimum to 200 eV during the minimum. From these observed
features, we discuss two possible causes of the X-ray minimum; the eclipse of
the X-ray plasma and an intrinsic fading of the X-ray emissivity. The drop in
the colliding wind X-ray emission also revealed the presence of an additional
X-ray component which exhibited no variation on timescales of weeks to years.
This component may be produced by the collision of high speed outflows at v
\~1000-2000 km s-1 from Eta Carinae with ambient gas within a few thousand AU
from the star.
