Pulse profile modelling of thermonuclear burst oscillations − I. The effect of neglecting variability

Kini, Yves; Salmi, Tuomo; Watts, Anna L.; Vinciguerra, S.; Choudhury, Devarshi; Fenne, Siem; Bogdanov, Slavko; Meisel, Zach; Suleimanov, V.

doi:10.1093/mnras/stad1030

Monthly Notices of the Royal Astronomical Society

2023

DOI: 10.1093/mnras/stad1030

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Pulse profile modelling of thermonuclear burst oscillations − I. The effect of neglecting variability

Yves Kini

Tuomo Salmi

Anna L. Watts

et al.

Abstract: We study the effects of the time-variable properties of thermonuclear X-ray bursts on modeling their millisecond-period burst oscillations. We apply the pulse profile modeling technique that is being used in the analysis of rotation-powered millisecond pulsars by the Neutron Star Interior Composition Explorer (NICER) to infer masses, radii, and geometric parameters of neutron stars. By simulating and analyzing a large set of models, we show that overlooking burst time-scale variability in temperatures and size… Show more

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Cited by 3 publications

References 123 publications

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Pulse profile modelling of thermonuclear burst oscillations – II. Handling variability

Kini,

Salmi,

Vinciguerra

et al. 2023

Monthly Notices of the Royal Astronomical Society

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Pulse profile modelling is a relativistic ray-tracing technique that can be used to infer masses, radii, and geometric parameters of neutron stars. In a previous study, we looked at the performance of this technique when applied to thermonuclear burst oscillations from accreting neutron stars. That study showed that ignoring the variability associated with burst oscillation sources resulted in significant biases in the inferred mass and radius, particularly for the high count rates that are nominally required to obtain meaningful constraints. In this follow-on study, we show that the bias can be mitigated by slicing the bursts into shorter segments where variability can be neglected, and jointly fitting the segments. Using this approach, the systematic uncertainties on the mass and radius are brought within the range of the statistical uncertainty. With about 106 source counts, this yields uncertainties of approximately 10 per cent for both the mass and radius. However, this modelling strategy requires substantial computational resources. We also confirm that the posterior distributions of the mass and radius obtained from multiple bursts of the same source can be merged to produce outcomes comparable to that of a single burst with an equivalent total number of counts.

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Pulse profile modelling of thermonuclear burst oscillations – II. Handling variability

Kini,

Salmi,

Vinciguerra

et al. 2023

Monthly Notices of the Royal Astronomical Society

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show abstract

Constraining the properties of the thermonuclear burst oscillation source XTE J1814−338 through pulse profile modelling

Kini,

Salmi,

Vinciguerra

et al. 2024

Monthly Notices of the Royal Astronomical Society

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Pulse profile modelling (PPM) is a comprehensive relativistic ray-tracing technique employed to determine the properties of neutron stars. In this study, we apply this technique to the Type I X-ray burster and accretion-powered millisecond pulsar J, extracting its fundamental properties using PPM of its thermonuclear burst oscillations. Using data from its 2003 outburst, and a single uniform temperature hot spot model, we infer J to be located at a distance of $7.2^{+0.3}_{-0.4}$ kpc, with a mass of $1.21^{+0.05}_{-0.05}$ M⊙ and an equatorial radius of $7.0^{+0.4}_{-0.4}$ km. Our results also offer insight into the time evolution of the hot spot but point to some potential shortcomings of the single uniform temperature hot spot model. We explore the implications of this result, including what we can learn about thermonuclear burst oscillation mechanisms and the importance of modelling the accretion contribution to the emission during the burst.

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The Radius of the High-mass Pulsar PSR J0740+6620 with 3.6 yr of NICER Data

Salmi,

Choudhury,

Kini

et al. 2024

ApJ

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We report an updated analysis of the radius, mass, and heated surface regions of the massive pulsar PSR J0740+6620 using Neutron Star Interior Composition Explorer (NICER) data from 2018 September 21 to 2022 April 21, a substantial increase in data set size compared to previous analyses. Using a tight mass prior from radio-timing measurements and jointly modeling the new NICER data with XMM-Newton data, the inferred equatorial radius and gravitational mass are 12.49 − 0.88 + 1.28 km and 2.073 − 0.069 + 0.069 M ⊙, respectively, each reported as the posterior credible interval bounded by the 16% and 84% quantiles, with an estimated systematic error ≲ 0.1 km. This result was obtained using the best computationally feasible sampler settings providing a strong radius lower limit but a slightly more uncertain radius upper limit. The inferred radius interval is also close to the R = 12.76 − 1.02 + 1.49 km obtained by Dittmann et al., when they require the radius to be less than 16 km as we do. The results continue to disfavor very soft equations of state for dense matter, with R < 11.15 km for this high-mass pulsar excluded at the 95% probability. The results do not depend significantly on the assumed cross-calibration uncertainty between NICER and XMM-Newton. Using simulated data that resemble the actual observations, we also show that our pipeline is capable of recovering parameters for the inferred models reported in this paper.

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Pulse profile modelling of thermonuclear burst oscillations − I. The effect of neglecting variability

Cited by 3 publications

References 123 publications

Pulse profile modelling of thermonuclear burst oscillations – II. Handling variability

Pulse profile modelling of thermonuclear burst oscillations – II. Handling variability

Constraining the properties of the thermonuclear burst oscillation source XTE J1814−338 through pulse profile modelling

The Radius of the High-mass Pulsar PSR J0740+6620 with 3.6 yr of NICER Data

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