X-ray spectrum from gamma Cassiopeiae

The X-ray source gamma Cassiopeiae was observed with the X-ray astronomy satellite Tenma. A strong iron line was observed at 6.8 keV with an intensity of 280 eV equivalent width as is expected from a highly ionized plasma. The strength of the iron line at 6.8 keV and the existence of a thin thermal plasma are in conflict with models that require a neutron star as the X-ray source. From many of the X-ray binaries with a neutron star, only a weak ionized iron line (less than 50 eV at 6.7 keV) or strong reprocessed iron line (6.4 keV) has been observed with Tenma. This Letter suggests the possible existence of a degenerate dwarf as a companion for gamma Cas instead of a neutron star. The lack of luminosity from the white dwarf companion is attributed to a nonspherical mass loss from the primary. 23 references