M31 Pixel Lensing Event OAB-N2: A Study of the Lens Proper Motion
Gould, A.; Nucita, A.; Mancini, L.; Dall'Ora, M.; Dominik, M.; Bozza, V.; De Paolis, F.; Ingrosso, G.; Sereno, M.; Bruni, I.; Jetzer, Ph.; Strafella, F.; Calchi Novati, S.; Scarpetta, G.; Gualandi, R.; Plan Collaboration
Italy, United States, United Kingdom, Switzerland, Spain
Abstract
We present an updated analysis of the M31 pixel lensing candidate event OAB-N2 previously reported by Calchi Novati et al. Here we take advantage of new data both astrometrical and photometrical. For astrometry: using archival 4 m KPNO and Hubble Space Telescope/WFPC2 data we perform a detailed analysis of the event source whose result, although not fully conclusive on the source magnitude determination, is confirmed by the following light curve photometry analysis. For photometry: first, unpublished WeCAPP data allow us to confirm OAB-N2, previously reported only as a viable candidate, as a well-constrained pixel lensing event.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 a 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.