  X-ray emission from the supermassive binary system Eta Carinae declines
sharply around periastron. This X-ray minimum has two distinct phases - the
lowest flux phase in the first ~3 weeks and a brighter phase thereafter. In
2009, the Chandra X-ray Observatory monitored the first phase five times and
found the lowest observed flux at ~1.9e-12 ergs cm-2 s-1 (3-8 keV). The
spectral shape changed such that the hard band above ~4 keV dropped quickly at
the beginning and the soft band flux gradually decreased to its lowest observed
value in ~2 weeks. The hard band spectrum had begun to recover by that time.
This spectral variation suggests that the shocked gas producing the hottest
X-ray gas near the apex of the wind-wind collision (WWC) is blocked behind the
dense inner wind of the primary star, which later occults slightly cooler gas
downstream. Shocked gas previously produced by the system at earlier orbital
phases is suggested to produce the faint residual X-ray emission seen when the
emission near the apex is completely blocked by the primary wind. The brighter
phase is probably caused by the re-appearance of the WWC plasma, whose
emissivity significantly declined during the occultation. We interpret this to
mean that the X-ray minimum is produced by a hybrid mechanism of an occultation
and a decline in emissivity of the WWC shock.
