THE X-RAY TIME VARIABILITY AND SPECTRUM OF GAMMA CASSIOPEIAE (X 0053+ 604)

A 30 h duration EXOSAT observation made in 1985 December is used to examine the X-ray time variability and spectrum of the Be star gamma Cassiopeiae (X 0053 + 604). We find that the X-ray lightcurve is dominated by irregular energy-independent flaring on time-scales greater than or similar to 100 s. This flaring markedly decreases the sensitivity to any periodic signals. We find no evidence for the 6000 s oscillations reported by Frontera et al. (1987) from an earlier EXOSAT observation. We suggest that these arise from statistical fluctuations in the red noise power. The X-ray spectrum of gamma Cas can either be modeled by thermal emission from an optically thin plasma with a temperature of 12 keV, or by a cut-off power-law model with a narrow iron line at an energy of 6.67 keV. The origin of the X-ray emission in this system remains open since its spectral and temporal properties are consistent with both an accreting neutron star and a white dwarf while its high temperature argues against a coronal mechanism.