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We report on the serendipitous discovery of a 442-Hz pulsar during a RossiX-ray Timing Explorer (RXTE) observation of the globular cluster NGC 6440. Theoscillation is detected following a burst-like event which was decaying at thebeginning of the observation. The time scale of the decay suggests we may haveseen the tail-end of a long-duration burst. Low-mass X-ray binaries (LMXBs) areknown to emit thermonuclear X-ray bursts that are sometimes modulated by thespin frequency of the star, the so called burst oscillations. The pulsationsreported here are peculiar if interpreted as canonical burst oscillations. Inparticular, the pulse train lasted for ~500 s, much longer than in standardburst oscillations. The signal was highly coherent and drifted down by ~2x10^-3Hz, much smaller than the ~Hz drifts typically observed during normal bursts.The pulsations are reminiscent of those observed during the much more energetic``superbursts'', however, the temporal profile and the energetics of the burstsuggest that it was not the tail end nor the precursor feature of a superburst.It is possible that we caught the tail end of an outburst from a new`intermittent'' accreting X-ray millisecond pulsar, a phenomenon which untilnow has only been seen in HETE J1900.1$-$2455 (Galloway et al. 2007). We notethat (Kaaret et al. 2003) reported the discovery of a 409.7 Hz burstoscillation from SAX J1748.9-2021, also located in NGC 6440. However, ChandraX-ray  Observatory imaging indicates it contains several point-like X-ray sources,thus the 442 Hz object is likely a different source.

Discovery of 442-Hz Pulsations from an X-ray Source in the Globular Cluster NGC 6440