M31 Pixel Lensing Event OAB-N2: A Study of the Lens Proper Motion

July 2010 • 2010ApJ...717..987C

Authors • Calchi Novati, S. • Dall'Ora, M. • Gould, A. • Bozza, V. • Bruni, I. • De Paolis, F. • Dominik, M. • Gualandi, R. • Ingrosso, G. • Jetzer, Ph. • Mancini, L. • Nucita, A. • Scarpetta, G. • Sereno, M. • Strafella, F. • Plan Collaboration

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 For photometry: first, unpublished WeCAPP data allow us to confirm OAB-N2, previously reported only as a viable candidate, as a well-constrained pixel lensing event.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.

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Sebastiano Calchi Novati

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