Aims . We seek to probe the Galactic bulge IMF starting from microlensing observations . Methods . We analyse the recent results of the microlensing campaigns carried out towards the Galactic bulge presented by the EROS , MACHO and OGLE collaborations .
In particular , we study the duration distribution of the events .
We assume a power law initial mass function , \xi ( \mu ) \propto \mu ^ { - \alpha } , and we study the slope \alpha both in the brown dwarf and in the main sequence ranges .
Moreover , we compare the observed and expected optical depth profiles . Results . The values of the mass function slopes are strongly driven by the observed timescales of the microlensing events .
The analysis of the MACHO data set gives , for the main sequence stars , \alpha = 1.7 \pm 0.5 , compatible with the result we obtain with the EROS and OGLE data sets , and a similar , though less constrained slope for brown dwarfs .
The lack of short duration events in both EROS and OGLE data sets , on the other hand , only allows the determination of an upper limit in this range of masses , making the overall result less robust .
The optical depth analysis gives a very good agreement between the observed and the expected values , and we show that the available data do not allow one to discriminate between different bulge models .