BeppoSAX broad-band observations of gamma Cassiopeiae

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 199 8 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 sign ificant residuals around 0.3 keV and 1 keV. The former is interpreted as th e 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 20 0+/-10 eV. However, a MEKAL interpretation gives a significantly lower temp erature 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 t he 2-10 keV band is 6x10(32) ergs s(-1). Simultaneous optical measurements by the Wendelstein Observatory near Munich, indicate that the source contin ues 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 wav elengths of 2.18+/-0.06, 2.23+/-0.02 and 2.36+/-0.03, respectively, confirm this.