The POINT-AGAPE Survey: Comparing Automated Searches of Microlensing Events toward M31

TL;DR

This paper compares three automated microlensing search methods toward M31, highlighting how different selection criteria influence candidate detection and emphasizing the subjectivity and variability in results.

Contribution

It provides a comparative analysis of three independent microlensing candidate selection methods on the same dataset, revealing the impact of cut choices on results.

Findings

Candidate numbers vary with selection cuts

Only two candidates are common across all analyses

Different analysis strategies lead to different candidate lists

Abstract

Searching for microlensing in M31 using automated superpixel surveys raises a number of difficulties which are not present in more conventional techniques. Here we focus on the problem that the list of microlensing candidates is sensitive to the selection criteria or "cuts" imposed and some subjectivity is involved in this. Weakening the cuts will generate a longer list of microlensing candidates but with a greater fraction of spurious ones; strengthening the cuts will produce a shorter list but may exclude some genuine events. We illustrate this by comparing three analyses of the same data-set obtained from a 3-year observing run on the INT in La Palma. The results of two of these analyses have been already reported: Belokurov et al. (2005) obtained between 3 and 22 candidates, depending on the strength of their cuts, while Calchi Novati et al. (2005) obtained 6 candidates. The third analysis is presented here for the first time and reports 10 microlensing candidates, 7 of which are new. Only two of the candidates are common to all three analyses. In order to understand why these analyses produce different candidate lists, a comparison is made of the cuts used by the three groups...