  We report broad-band X-ray measurements of the Be star Gamma Cassiopeiae by
the BeppoSAX X-ray astronomy satellite. The observations took place on 1998
July, 18-23. The 0.1-200 keV X-ray spectrum is reasonably well fit by an
optically thin thermal plasma model of temperature 12.5 +/- 0.6 keV with
significant residuals around 0.3 keV and 1 keV. The former is interpreted as
the variable soft component reported by ROSAT, although there is no evidence
for variability at the 5 % level. For a blackbody interpretation, the fitted
temperature is 100 +320 -13 eV, in agreement with the ROSAT value of 200 +/- 10
eV. However, a MEKAL interpretation gives a significantly lower temperature of
(48 +/- 11 eV). The fitted abundances are about half solar values, in agreement
with previous measurements. At higher energies, the spectrum does not require
non-thermal components and the observation of a line at 6.8 keV supports the
ASCA interpretation of the source as an accreting white dwarf. Assuming a
source distance of 188 pc, the bolometric luminosity in the 2-10 keV band is 6
10^32 erg/s. Simultaneous optical measurements by the Wendelstein Observatory
near Munich, indicate that the source continues to be in a late but rather
normal Be phase, with no obvious signs of a transition to the Be-shell phase.
The measured magnitudes at B, V and R wavelengths of 2.18 +/- 0.06, 2.23 +/-
0.02 and 2.36 + /- 0.03, respectively, confirm this.
