Measuring the neutron star equation of state using X-ray timing

By A. Watts, N. Andersson, D. Chakrabarty, M. Feroci, K. Hebeler, G. Israel, F. Lamb, M. Miller, S. Morsink, F. Özel and 8 more. 2016

215 citations recorded by the source corpus.

One of the primary science goals of the next generation of hard X-ray timing instruments is to determine the equation of state of the matter at supranuclear densities inside neutron stars, by measuring the radius of neutron stars with different masses to accuracies of a few percent. Three main techniques can be used to achieve this goal. The first involves waveform modelling. The flux we observe from a hotspot on the neutron star surface offset from the rotational pole will be modulated by the star's rotation, giving rise to a pulsation. Information about mass and radius is encoded into the pulse profile via relativistic effects, and tight constraints on mass and radius can be obtained. The second technique involves characterising the spin distribution of accreting neutron stars. The most rapidly rotating stars provide a very clean constraint, since the mass-shedding limit is a function of mass and radius. However the overall spin distribution also provides a guide to the torque mechanisms in operation and the moment of inertia, both of which can depend sensitively on dense matter physics. The third technique is to search for quasi-periodic oscillations in X-ray flux associated with global seismic vibrations of magnetars (the most highly magnetized neutron stars), triggered by magnetic explosions. The vibrational frequencies depend on stellar parameters including the dense matter equation of state. We illustrate how these complementary X-ray timing techniques can be used to constrain the dense matter equation of state, and discuss the results that might be expected from a 10m$^2$ instrument. We also discuss how the results from such a facility would compare to other astronomical investigations of neutron star properties. [Modified for arXiv]

Subfields: Astronomy and Astrophysics, Geophysics

View Paper: https://www.semanticscholar.org/paper/47fff77e80143e0513ea28955f8f031d851725ba

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In Astronomy and Astrophysics

1. J. Lattimer
2. A. Watts
3. Bao-An Li
4. Nai-Bo Zhang
5. S. Guillot
6. Jun Xu
7. A. Steiner
8. C. Heinke

In Geophysics

1. Bao-An Li
2. Nai-Bo Zhang
3. A. Watts
4. Jun Xu
5. J. Lattimer
6. S. Guillot
7. A. Steiner
8. T. Strohmayer

Citations in the corpus

• A NICER View of PSR J0030+0451: Millisecond Pulsar Parameter Estimation (2019, background): “…burst oscillations are radiatively harder (∼ 1–30 keV) than the pulsations of MSPs. Accumulating the requisite number of photons for tight constraints, in a realistic observing time, also requires a telescope with an effective area of several square meters (Watts et al. 2016; Watts 2019).”
• Equation of state sensitivities when inferring neutron star and dense matter properties (2018, methodology): “Given good relativistic ray-tracing models for rapidly rotating neutron star space-times, it is possible to perform Bayesian inference of EOS parameters using the pulse profile data (see Watts et al. 2016, and references therein).”
• Combined Constraints on the Equation of State of Dense Neutron-rich Matter from Terrestrial Nuclear Experiments and Observations of Neutron Stars (2018, background): “(Lattimer & Prakash 2016; Oertel et al. 2017; Özel & Freire 2016; Watts et al. 2016; Grigorian et al. 2016; Newton et al. 2014) for recent reviews.”
• A NICER View of PSR J0030+0451: Implications for the Dense Matter Equation of State (2019, methodology): “…encode information about the spacetime into the phase-energy resolved pulse-profile.18 Pulse-profile modeling employs relativistic ray-tracing and Bayesian inference software to jointly infer mass and radius (see Bogdanov 2016; Watts et al. 2016; Watts 2019, for an overview of the technique).”
• From hadrons to quarks in neutron stars: a review (2017, unknown): “Beyond simple estimates of radius based on spectroscopic analyses of photons from neutron stars in quiescence (see [20] and references therein), further information on the relation can be gained from following the evolution of thermonuclear x-ray bursts on the surfaces of accreting neutron stars in ”
• Constraining the mass and radius of neutron stars in globular clusters (2017, background): “H The central density of all neutron stars, however, is likely to be larger than four times the nuclear saturation density (Steiner et al. 2015; Watts et al. 2016).”