We present a new method of matching observations of Type-I (thermonuclear) X-ray bursts with models, comparing the predictions of a semi-analytic ignition model with X-ray observations of the accretion-powered millisecond pulsar SAX J1808.4-3658 in outburst. We used a Bayesian analysis approach to marginalize over the parameters of interest and determine parameters such as fuel composition, distance/anisotropy factors, neutron star mass, and neutron star radius. Our study includes a treatment of the system inclination effects, inferring that the rotation axis of the system is inclined (69+−42 )◦ from the observers line of sight, assuming a flat disc model. This method can be applied to any accreting source that exhibits Type-I X-ray bursts. We find a hydrogen mass fraction of 0.57+−001314 and CNO metallicity of 0.013+−00006004 for the accreted fuel is required by the model to match the observed burst energies, for a distance to the source of 3.3+−0032 kpc. We infer a neutron star mass of 1.5+−0063 M☉ and radius of 11.8+−1039 km for a surface gravity of 1.9+−0074 × 1014 cm s−2 for SAX J1808.4-3658.
- Pulsars: individual: SAX J1808.4-3658
- X-rays: binaries
- X-rays: bursts