Optical identification of the X-ray burster in the globular cluster NGC 1851

We have obtained exposures of the field of X0512-401 in the globular cluste r NGC 1851, in X-rays with the Chandra X-Ray Observatory, and in the far-UV with the Hubble Space Telescope. We derive an accurate new X-ray position (within similar to1") for X0512-401, which enables us to confirm that the o nly plausible candidate for the optical/UV counterpart is star A, which we previously identified from Wide Field Planetary Camera 2 imaging. We find n o evidence for X-ray or UV flux modulation on the ultrashort (less than or similar to1 hr) expected binary period, which implies a low system inclinat ion. In addition, we have detected and spatially resolved an X-ray burst ev ent, confirming the association of the burster, quiescent X-ray source, and optical object. The very large of L-X/L-opt of this object implies an extr aordinarily compact system, similar to the sources in NGC 6624 and NGC 6712 .