Neutron star model atmospheres - a comparison with MXB 1728-34

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Abstract
A detailed comparison between the X-ray spectra calculated for model atmospheres in neutron stars and the observed spectra of X-ray bursts is presented. Comptonization and free–free absorption and emission processes are taken into account, as are the effects of iron in its last three states of ionization. Two types of model are formulated: (i) a constant density atmosphere and (ii) an atmosphere in approximate hydrostatic equilibrium. We obtain general correction formulae between colour temperature and effective temperature by folding the model spectra through the EXOSAT detector response. We have fitted the models to X-ray burst data obtained with EXOSA 7 from the source MXB 1728-34. We show that it is possible simultaneously to fit a sub-Eddington burst luminosity, a neutron star radius consistent with current equations of state, and a distance in agreement with optical estimates.

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