M31 pixel lensing event OAB-N2: a study of the lens proper motion
  We present an updated analysis of the M31 pixel lensing candidate event
OAB-N2 previously reported in Calchi Novati et al. (2009). Here we take
advantage of new data both astrometric and photometric. Astrometry: using
archival 4m-KPNO and HST/WFPC2 data we perform a detailed analysis on the event
source whose result, although not fully conclusive on the source magnitude
determination, is confirmed by the following light curve photometry analysis.
Photometry: first, unpublished WeCAPP data allows us to confirm OAB-N2,
previously reported only as a viable candidate, as a well constrained pixel
lensing event. Second, this photometry enables a detailed analysis in the event
parameter space including the effects due to finite source size. The combined
results of these analyses allow us to put a strong lower limit on the lens
proper motion. This outcome favors the MACHO lensing hypothesis over self
lensing for this individual event and points the way toward distinguishing
between the MACHO and self-lensing hypotheses from larger data sets.
