The POINT-AGAPE survey: 4 high signal-to-noise microlensing candidates detected towards M 31

¹ Laboratoire de Physique Corpusculaire et Cosmologie, Collège de France, 11 place Marcelin Berthelot, 75231 Paris, France
² CERN, 1211 Genève, Switzerland
³ Astronomy Unit, School of Mathematical Sciences, Queen Mary, University of London, Mile End Road, London E1 4NS, UK
⁴ Université Bretagne-Sud, campus de Tohannic, BP 573, 56017 Vannes Cedex, France
⁵ Theoretical Physics, 1 Keble Road, Oxford OX1 3NP, UK
⁶ Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK
⁷ Department of Astronomy, Ohio State Univ., 140 West 18th Avenue, Columbus, OH 43210, USA
⁸ Astrophysics Research Institute, Liverpool John Moores Univ., 12 Quays House, Egerton Wharf, Birkenhead CH41 1LD, UK
⁹ LERMA, FRE2460, Obs. de Paris, 61 avenue de l'Observatoire, 75014 Paris, France
¹⁰ Laboratoire d'Astrophysique UMR CNRS 5572, Obs. Midi-Pyrénées, 14 avenue Édouard Belin, 31400 Toulouse, France

Corresponding author: S. Paulin-Henriksson, paulin@cdf.in2p3.fr

Received: 1 July 2002
Accepted: 3 April 2003

Abstract

We have carried out a survey of the Andromeda galaxy for unresolved microlensing (pixel lensing). We present a subset of four short timescale, high signal-to-noise microlensing candidates found by imposing severe selection criteria: the source flux variation exceeds the flux of an  magnitude star and the full width at half maximum timescale is less than 25 days. Remarkably, in three out of four cases, we have been able to measure or strongly constrain the Einstein crossing time of the event. One event, which lies projected on the M 31 bulge, is almost certainly due to a stellar lens in the bulge of M 31. The other three candidates can be explained either by stars in M 31 and M 32 or by MACHOs.