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Type I X-ray bursts are thermonuclear flashes observed from the surfaces ofaccreting neutron stars (NSs) in Low Mass X-ray Binaries. Oscillations havebeen observed during the rise and/or decay of some of these X-ray bursts. Thoseseen during the rise can be well explained by a spreading hot spot model, butlarge amplitude oscillations in the decay phase remain mysterious because ofthe absence of a clear-cut source of asymmetry. To date there have not been anyquantitative studies that consistently track the oscillation amplitude bothduring the rise and decay (cooling tail) of bursts. Here we compute the lightcurves and amplitudes of oscillations in X-ray burst models that realisticallyaccount for both flame spreading and subsequent cooling. We present results forseveral such "cooling wake" models, a "canonical" cooling model where eachpatch on the NS surface heats and cools identically, or with alatitude-dependent cooling timescale set by the local effective gravity, and an"asymmetric" model where parts of the star cool at significantly differentrates. We show that while the canonical cooling models can generateoscillations in the tails of bursts, they cannot easily produce the highestobserved modulation amplitudes. Alternatively, a simple phenomenological modelwith asymmetric cooling can achieve higher amplitudes consistent with theobservations.

X-ray Burst Oscillations: From Flame Spreading to the Cooling Wake