1 Research context

The idea of using gravitational microlensing as a tool to probe the dark matter in the Galactic halo goes back to 1986 with a paper by B. Paczynski (Paczynski 1986). Since then, several experiments have been monitoring millions of stars towards the Large and Small Magellanic Clouds ( LMC and SMC) and candidates have been observed towards the two targets (Alcock et al. 1993; Aubourg et al. 1993; Ansari et al. 1996; Alcock et al. 1997a; Afonso et al. 1999; Lasserre et al. 2000).

The detection of candidates towards the LMC suggested a population of lenses accounting for $\sim$20% of a standard halo, with a most probable mass between 0.2 and 0.9 $M_\odot$ (Alcock et al. 2000). Results by Lasserre et al. (2000) show that objects up to 1 $M_\odot$ cannot account for more than 40% of a standard halo. These lenses cannot be ordinary Galactic stars, whose density is much too low to account for the observed optical depth, and Goldman et al. (2002) demonstrated they cannot be halo white dwarfs with a hydrogen atmosphere. Much debate has occurred on the nature and the location of the lenses, the main two possibilities being 0.4 $M_\odot$ dark objects in the halo or stars at the low mass end of the main sequence in the clouds themselves (Sahu 1994; Wu 1994).

This makes the SMC a very valuable target. While the characteristics (optical depth and duration) of events towards the two clouds should be similar for halo lenses (Sackett & Gould 1993), the different dynamical properties of the clouds could account for differences if the events are due to self-lensing.

The EROS 2 experiment has been surveying the SMC since 1996. We present here an analysis of five years of data accumulated towards this target.