  We report the detection of pulsations at 552 Hz in the rising phase of two
type-I (thermonuclear) X-ray bursts observed from the accreting neutron star
EXO 0748-676 in 2007 January and December, by the Rossi X-ray Timing Explorer.
The fractional amplitude was 15% (rms). The dynamic power density spectrum for
each burst revealed an increase in frequency of approx. 1-2 Hz while the
oscillation was present. The frequency drift, the high significance of the
detections and the almost identical signal frequencies measured in two bursts
separated by 11 months, confirms this signal as a burst oscillation similar to
those found in 13 other sources to date. We thus conclude that the spin
frequency in EXO 0748-676 is within a few Hz of 552 Hz, rather than 45 Hz as
was suggested from an earlier signal detection by Villarreal & Strohmayer
(2004). Consequently, Doppler broadening must significantly affect spectral
features arising from the neutron star surface, so that the narrow absorption
features previously reported from an XMM-Newton spectrum could not have arisen
there. The origin of both the previously reported 45 Hz oscillation and the
X-ray absorption lines is now uncertain.
