Spectral analysis of x-ray bursts from Ser X-1

Some further results of the spectral analysis for X-ray bursts detected from Ser X-1/MXB 1837+05 by the SAS-3 satellite are presented. The observed variations of the maximum flux indicate that the emission area A can change from burst to burst. The colour temperature Ta obtained from the spectral analysis during the maximum flux is higher than the black-body temperature Tam by the emissivity factor ε = (Tam/Ta/)4. The maximum black-body temperature Tam obtained for a particular model of a neutron star M = 1.4 Msun and R = 10 km is 1.63 keV, and cannot be exceeded. It is a natural consequence of our general assumption that k=F/max/FEd is less than or equal to unity for all the bursts known from Ser X-1 data. The Eddington luminosity LEd is apparently exceeded for some observed bursts. This is due to variations of two quantities, the emissivity factor and the fractional emission area fa = A/4πR2/sub a/. In the case of Serpens X-1, for k = 1, the mean values of ε and fa are 0.30+-0.25 and 0.95+-0.27, respectively. The large spread of ε indicates the differences between some physical conditions fulfill each burst regime. (author)