The formation of iron features in the cooling spectrum of X-ray bursts.

Abstract

A detailed calculation of the formation and detection of iron spectral features in X-ray bursts is presented. Observation of these features will enable the mass and radius of a neutron star to be estimated separately. Comptonization and free-free absorption and emission processes are taken into account, as well as the effects of iron in its last four states of ionization. The authors estimate the size of detector, with response similar to that of the EXOSAT ME, needed in order to observe the iron features. The large-area detectors on GINGA should meet this requirement. The authors show that the absorption feature reported at 4.1 keV from MXB 1636-536 has an equivalent width much larger than expected from Fe XXV.