A Bayesian approach to matching thermonuclear X-ray burst observations with models

A. J. Goodwin, D. K. Galloway, A. Heger, A. Cumming, Z. Johnston

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11 Citations (Scopus)

Abstract

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.

Original languageEnglish
Pages (from-to)2228-2240
Number of pages13
JournalMonthly Notices of the Royal Astronomical Society
Volume490
Issue number2
DOIs
Publication statusPublished - 1 Dec 2019

Keywords

  • Pulsars: individual: SAX J1808.4-3658
  • X-rays: binaries
  • X-rays: bursts

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