Toshiaki Murakami

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.

Delays of Optical Bursts in Simultaneous Optical and X-Ray Observations of MXB 1636-53

Observations of simultaneous optical and X-ray bursts from 4U/MXB 1636-53 were made using the Hakucho burst monitor system and optical telescopes at the European Southern Observatory during 1979 and 1980. The six best cases among the 10 coinciding observations are analyzed in terms of a model in which the optical emission is the result of reprocessing of X-rays (through blackbody heating). From this analysis, the temperature (spatially averaged) and size of a reprocessor, and the smearing and delay of the optical bursts are obtained. For the maximum temperatures of the optical reprocessor, the values differ from burst to burst, ranging from about 3 x 10 to the 4th to about 10 to the 5th K. The present analysis suggests that the size of the reprocessor varies by a factor of a few. For the smearing of the optical bursts an upper limit of a few seconds is derived. The most important result of this analysis is that the delay times are not the same for all bursts. The possible constraints which these results put on a low-mass binary model of this burst source are discussed.