  We report the discovery of a short-duration microlensing candidate in the
northern field of the POINT-AGAPE pixel lensing survey towards M31. The
full-width half-maximum timescale is very short, just 1.8 days. Almost
certainly, the source star has been identified on Hubble Space Telescope
archival images, allowing us to infer an Einstein crossing time of 10.4 days, a
maximum magnification of about 18, and a lens-source proper motion greater than
0.3 microarcsec/day. The event lies projected at 8' from the center of M31,
which is beyond the bulk of the stellar lens population. The lens is likely to
reside in one of three locations. It may be a star in the M31 disk, or a
massive compact halo object (Macho) in either M31 or the Milky Way. The most
probable mass is 0.06 solar masses for an M31 Macho, 0.02 solar masses for a
Milky Way Macho and 0.2 solar masses for an M31 stellar lens. Whilst the
stellar interpretation is plausible, the Macho interpretation is the most
probable for halo fractions above 20%.
