Systematic Analysis of 22 Microlensing Parallax Candidates

We attempt to identify all microlensing parallax events for which the parallax fit improves ∆χ > 100 relative to a standard microlensing model. We outline a procedure to identify three types of discrete degeneracies (including a new one that we dub the “ecliptic degeneracy”) and find many new degenerate solutions in 16 previously published and 6 unpublished events. Only four events have one unique solution and the other 18 events have a total of 44 solutions. Our sample includes three previously identified black-hole (BH) candidates. We consider the newly discovered degenerate solutions and determine the relative likelihood that each of these is a BH. We find the lens of event MACHO-99-BLG-22 is a strong BH candidate (78%), event MACHO-96-BLG-5 is a marginal BH candidate (37%), and MACHO-98-BLG-6 is a weak BH candidate (2.2%). The lens of event OGLE-2003-BLG-84 may be a Jupiter-mass free-floating planet candidate based on a weak 3σ detection of finite-source effects. We find that event MACHO-179-A is a brown dwarf candidate within ∼ 100 pc of the Sun, mostly due to its very small projected Einstein radius, r̃E = 0.23±0.05AU. As expected, these microlensing parallax events are biased toward lenses that are heavier and closer than average. These events were examined for xallarap (or binary-source motion), which can mimic parallax. We find that 23% of these events are strongly affected by xallarap. Subject headings: gravitational lensing — parallax Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA, (sdp,gould)@astronomy.ohio-state.edu Max-Planck fuer Astronomie, Koenigstuhl 17, 69117 Heidelberg, Germany, [email protected] Department of Physics, Notre Dame University, Notre Dame, IN 46566, USA, [email protected] DAPNIA-SPP, CE-Saclay, F-91191 Gif-sur-Yvette, France, [email protected] Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa, Poland, (udalski,msz)@astrouw.edu.pl