Constraints on the parameters of X-ray burster emission regions

The neutron star mass-radius relations used in the present investigation are taken from a study conducted by Arnett and Bowers (1974). The emission region of an X-ray burster is characterized by three quantities, including the ratio of the emitted flux to the Eddington flux, the blackbody emissivity, and the fraction of the emitting surface which is at a distance R from the center of the compact object. Combined with flux and distance information one may place constraints on the X-ray emission region for each burster individually. Relativistic calculations transform the observed 'apparent areas' (as calculated from blackbody spectral fits) into limits on the fraction of the neutron star's surface involved in the emission. If the emission regions are actually Eddington limited, then either the emissivities are all very small or there are strong magnetic fields present, decreasing the scattering opacity. This result is independent of the size and shape of the emission region and also the burster's distance.