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Title:Accretion- and nuclear-powered phenomena in neutron stars with millisecond spin periods
Author(s):Lo, Ka-Ho
Director of Research:Lamb, Frederick K.
Doctoral Committee Chair(s):Stack, John D.
Doctoral Committee Member(s):Lamb, Frederick K.; Fields, Brian D.; Thaler, Jonathan J.
Department / Program:Physics
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):neutron stars
dense matter
equation of state
millisecond pulsars
Large Observatory for X-ray Timing (LOFT)
Abstract:Analysis of observations of the X-ray emission produced by accreting neutron stars with millisecond spin periods can provide important information about the masses M and radii R of neutron stars, thereby yielding uniquely valuable information about the still uncertain properties of cold matter at several times the density of nuclear matter; about the evolution of neutron star magnetic fields and spin rates; and about the physics of accretion onto these stars, which are found in close, low-mass binary star systems. Avenues for obtaining this information include modeling the accretion- and nuclear-powered millisecond X-ray brightness oscillations produced by some of these stars and the spectra of their nuclear-powered emission, and then comparing these models with high-quality X-ray data. In this thesis, I explore the so-called "nearly aligned moving spot model" that has been proposed to explain many of the observed properties of the accretion-powered millisecond X-ray brightness oscillations produced by some accreting neutron stars in close, low-mass binary star systems and compare the properties this model predicts with the observed properties of these stars. I also study the accuracy and precision with which M and R can be determined by analyzing energy-resolved waveforms of the X-ray brightness oscillations seen during some of the thermonuclear X-ray bursts produced by some of these neutron stars. Finally, I describe how comparison of high-precision measurements of X-ray burst spectra with the spectra predicted by high-precision model atmosphere calculations can be used to constrain M and R. I find that many observed properties of the accretion-powered millisecond X-ray oscillations can be successfully explained by a model in which the X-ray emitting areas on the neutron star surface are close to the star's rotation pole but wander. I find that M and R can be tightly constrained by analyzing energy-resolved X-ray burst oscillation waveform data measured by a future X-ray satellite instrument having 2-30 keV energy coverage and an effective area of 10 m^2, such as the proposed LOFT or AXTAR missions, provided the hot spots that produce these oscillations are not too far from the star's rotation equator. The precision of these M and R measurements can be increased substantially by independent knowledge of the inclination and other properties of the system. Finally, I find that the detailed model atmosphere spectra computed by Suleimanov et al. (2012) provide excellent descriptions of the most precise spectra of X-ray bursts that are currently available, verifying these models and potentially allowing M and R to be constrained using them. I explain the methodology used, describe the results, and discuss their implications.
Issue Date:2013-08-22
Rights Information:Copyright 2013 Ka-Ho Lo
Date Available in IDEALS:2013-08-22
Date Deposited:2013-08

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