M31 pixel lensing event OAB-N2: a study of the lens proper motion

TL;DR

This paper provides an updated analysis of the M31 pixel lensing event OAB-N2, combining new astrometric and photometric data to constrain the lens proper motion and distinguish between MACHO and self-lensing hypotheses.

Contribution

It introduces a comprehensive analysis using new data to better constrain the lens proper motion and differentiate lensing models in M31.

Findings

Confirmed OAB-N2 as a well-constrained pixel lensing event.

Established a strong lower limit on the lens proper motion.

Favors the MACHO lensing hypothesis over self-lensing for this event.

Abstract

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 Photometry: first, unpublished WeCAPP data allows us to confirm OAB-N2, previously reported only as a viable candidate, as a well constrained pixel lensing event.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