Determining Neutron Star Properties by Fitting Oblate-Star Waveforms To X-ray Burst Oscillations

M. Coleman Miller; Frederick K. Lamb

doi:10.1088/0004-637X/808/1/31

paper

Determining Neutron Star Properties by Fitting Oblate-Star Waveforms To X-ray Burst Oscillations

arXiv:1407.2579 · doi:10.1088/0004-637X/808/1/31

Abstract

We describe sophisticated new Bayesian analysis methods that make it possible to estimate quickly the masses and radii of rapidly rotating, oblate neutron stars by fitting oblate-star waveform models to energy-resolved observations of the X-ray oscillations produced by a hot spot on such stars. We conclude that models that take the oblate shape of the star into account should be used for stars with large radii and rotation rates $> 300$ Hz. We find that a 25% variation of the temperature of the hot spot with latitude does not significantly bias estimates of the mass $M$ and equatorial radius $R_{eq}$ derived by fitting a model that assumes a uniform-temperature spot. Our results show that fits of oblate-star waveform models to waveform data can simultaneously determine $M$ and $R_{eq}$ with uncertainties $≲$ 7% if (1) the star's rotation rate is $≳$ $600$ Hz; (2) the spot center and observer's sightline are both within $3 0^{\circ}$ of the star's rotational equator; (3) the oscillations have a fractional rms amplitude $≳$ 10%; and (4) $≳$ $1 0^{7}$ counts are collected from the star. This is a realistic fractional amplitude, and this many counts could be obtained from a single star by the accepted NICER and proposed LOFT and AXTAR space missions by combining data from many X-ray bursts. These uncertainties are small enough to improve substantially our understanding of cold, ultradense matter.

46 pages, 5 figures, accepted by The Astrophysical Journal

Determining Neutron Star Properties by Fitting Oblate-Star Waveforms To X-ray Burst Oscillations

Abstract

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