The mass and radius of a neutron star in X-ray burster MXB 1636 - 536

Abstract

The observational data of the X-ray burst source MXB 1636 - 536, obtained from the Tenma satellite, have been used to place constraints on the mass and radius of a neutron star. The results of theoretical models for the emergent spectral energy distribution for bursting neutron stars are combined with the transverse Doppler and gravitational redshift interpretation of the 4.1 keV absorption line. Under the assumption that the peak burst luminosity is limited to the Eddington value and that the absorption feature is formed in a region rotating at the Keplerian velocity, we find a neutron star mass and radius of 1.45 M<SUB>sun</SUB> and 10.3 km. If these two theoretical assumptions are satisfied to high accuracy (so that systematic errors are not large), then the formal errors in the analysis lead to a mass and radius range from 1.28 to 1.65 M<SUB>sun</SUB> and from 9.1 to 11.3 km, respectively. These neutron star properties are consistent with the Friedman and Pandharipande neutron and nuclear interaction model for the equation of state.