  An unusual Eddington-limited thermonuclear X-ray burst was detected from the
accreting neutron star in 2S 0918-549 with the Rossi X-ray Timing Explorer. The
burst commenced with a brief (40 ms) precursor and maintained near-Eddington
fluxes during the initial 77 s. These characteristics are indicative of a
nova-like expulsion of a shell from the neutron star surface. Starting 122 s
into the burst, the burst shows strong (87 +/- 1% peak-to-peak amplitude)
achromatic fluctuations for 60 s. We speculate that the fluctuations are due to
Thompson scattering by fully-ionized inhomogeneities in a resettling accretion
disk that was disrupted by the effects of super-Eddington fluxes. An expanding
shell may be the necessary prerequisite for the fluctuations.
