Inferring system parameters from the bursts of the accretion-powered pulsar IGR J17498-2921

TL;DR

This study uses an advanced simulation comparison method to analyze thermonuclear bursts from accretion-powered pulsars, constraining system parameters and revealing insights into neutron star properties and system evolution.

Contribution

It develops and applies the beansp code to infer detailed system parameters from burst observations, improving constraints on neutron star and binary system characteristics.

Findings

Good agreement with a hydrogen-deficient fuel model for IGR J17498-2921.

Revised distance estimate for SAX J1808.4-3658 at 2.7 kpc.

Constraints on neutron star mass and system inclination.

Abstract

Thermonuclear (type-I) bursts exhibit properties that depend both on the local surface conditions of the neutron stars on which they ignite, as well as the physical parameters of the host binary system. However, constraining the system parameters requires a comprehensive method to compare the observed bursts to simulations. We have further developed the beansp code for this purpose and analysed the bursts observed from IGR J17498-2921, a 401-Hz accretion-powered pulsar, discovered during it's 2011 outburst. We find good agreement with a model having H-deficient fuel with X = 0.15 +/- 0.4, and CNO metallicity Z=0.0014^{+0.0004}_{-0.0003}, about a tenth of the solar value. The model has the system at a distance of 5.7^{+0.6}_{-0.5} kpc, with a massive (approx. 2 M_sun) neutron star and a likely inclination of 60 deg. We also re-analysed the data from the 2002 outburst of the accretion-powered millisecond pulsar SAX J1808.4-3658. For that system we find a substantially closer distance than previously inferred, at 2.7 +/- 0.3 kpc, likely driven by a larger degree of burst emission anisotropy. The other system parameters are largely consistent with the previous analysis. We briefly discuss the implications for the evolution of these two systems.