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M. Muno (MIT), F. Ozel (IAS), D. Chakrabarty (MIT)
In this talk, I will present results from a study of 59 burst oscillations from six sources observed with the Rossi X-Ray Timing Explorer. The oscillations, which occur primarily during the decay of the bursts, exhibit amplitudes as large as 15%, disappearing after a few seconds because of intrinsic variations in their fractional amplitudes. I will show the combined folded profiles derived from all of the oscillations seen in each source. Using these pulse profiles, I obtain upper limits on the fractional amplitudes of harmonic and half-frequency signals of 0.3% and 0.6%, respectively. These correspond to less than 5% of the strongest signal at integer harmonics and less than 10% of the main signal at half-integer harmonics. Comparing the pulse morphologies with theoretical profiles calculated for various brightness patterns on the surface of a rotating neutron star, I place strong constraints on the geometry of thermonuclear bursts. I then discuss how these geometric constraints challenge current models for the production of surface brightness variations during the cooling phases of X-ray bursts.
Bulletin of the American Astronomical Society,
© 2003. The American Astronomical Soceity.