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We re-analyze the M31 microlensing event WeCAPP-GL1/Point-AGAPE-S3 taking into account that stars are not point-like but extended. We show that the finite size of stars can dramatically change the self-lensing eventrate and (less dramatically) also the halo lensing eventrate, if events are as bright as WeCAPP-GL1. The brightness of the brightest events mostly depends on the source sizes and fluxes and on the distance distribution of sources and lenses and therefore can be used as a sensitive discriminator between halo-lensing and self-lensing events, provided the stellar population mix of source stars is known well enough. Using a realistic model for the 3D-light distribution, stellar population and extinction of M31, we show that an event like WeCAPP-GL1 is very unlikely to be caused by self-lensing. In the entire WeCAPP-field ($17.2times 17.2$ centered on the bulge) we expect only one self-lensing event every 49 years with the approximate parameters of WeCAPP-GL1 (time-scale 1-3d, $R$ flux-excess <19.0 mag). If we assume only 20% of the dark halos of M31 and the Milky-Way consist of 1 solar mass MACHOs an event like WeCAPP-GL1 would occur every 10 years. Further more, if one uses position, FWHM time scale, flux excess and color of WeCAPP-GL1, self-lensing is even 13 times less likely than lensing by a MACHO, if MACHOs contribute 20% to the total halo mass and have masses in the range of 0.1 to 4 solar masses. We also demonstrate that (i) the brightness distribution of events in general is a good discriminator between self and halo lensing (ii) the time-scale distribution is a good discriminator if the MACHO mass is larger than 0.5 solar masses. Future surveys of M31 like PAndromeda (Pan-STARRS 1) should be able to provide many more such events within the next 4 years.
The POINT-AGAPE collaboration is carrying out a search for gravitational microlensing toward M31 to reveal galactic dark matter in the form of MACHOs (Massive Astrophysical Compact Halo Objects) in the halos of the Milky Way and M31. A high-threshold
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 sele
An automated search is carried out for microlensing events using a catalogue of 44554 variable superpixel lightcurves derived from our three-year monitoring program of M31. Each step of our candidate selection is objective and reproducible by a compu
The POINT-AGAPE survey is an optical search for gravitational microlensing events towards the Andromeda Galaxy (M31). As well as microlensing, the survey is sensitive to many different classes of variable stars and transients. Here we describe the au
The POINT-AGAPE collaboration has been monitoring M31 for three seasons with the Wide Field Camera on the Isaac Newton Telescope. In each season, data are taken for one hour per night for roughly sixty nights during the six months that M31 is visible