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S. Bhattacharyya (Dept. of Astronomy, UMD), T.E. Strohmayer (GSFC, NASA), M.C. Miller (Dept. of Astronomy, UMD), C.B. Markwardt (Dept. of Astronomy, UMD; GSFC, NASA)
Detailed modeling of the millisecond brightness oscillations during thermonuclear bursts from low mass X-ray binaries can provide important information about neutron star structure. Until now the implementation of this idea has not been entirely successful, largely because of the negligible harmonic content in burst oscillation lightcurves. However, the recent discovery of non-sinusoidal burst oscillation lightcurves from the accreting millisecond pulsar XTE J1814-338 has changed this situation. We, therefore, for the first time, make use of this opportunity to constrain neutron star parameters effectively. In our detailed study of the lightcurves of 22 bursts, we fit the burst oscillation lightcurves with fully general relativistic models that include light-bending and frame-dragging for lightcurve calculation, and compute numerically the structure of neutron stars using realistic equations of state. We find that at the 90% confidence level, Rc2/GM > 4.4 for the neutron star in XTE J1814-338. We also find evidence that the photons from the thermonuclear flash come out through the layers of accreted matter under conditions of Thomson scattering, and show that the secondary companion is a hydrogen burning main sequence star, with possible bloating (probably due to X-ray heating). We conclude by discussing the constraints on neutron star structure that would be possible with future high-area timing missions. This work was supported in part by NSF grant AST0098436.
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Bulletin of the American Astronomical Society, 36 #3
© 2004. The American Astronomical Soceity.