  We use RHESSI high-resolution imaging and spectroscopy observations from ~5
to 100 keV to characterize the hot thermal plasma during the 2002 July 23 X4.8
flare. These measurements of the steeply falling thermal X-ray continuum are
well fit throughout the flare by two distinct isothermal components: a
super-hot (T > 30 MK) component that peaks at ~44 MK and a lower-altitude hot
(T < 25 MK) component whose temperature and emission measure closely track
those derived from GOES measurements. The two components appear to be spatially
distinct, and their evolution suggests that the super-hot plasma originates in
the corona, while the GOES plasma results from chromospheric evaporation.
Throughout the flare, the measured fluxes and ratio of the Fe and Fe-Ni
excitation line complexes at ~6.7 and ~8 keV show a close dependence on the
super-hot continuum temperature. During the pre-impulsive phase, when the
coronal thermal and non-thermal continua overlap both spectrally and spatially,
we use this relationship to obtain limits on the thermal and non-thermal
emission.
