  The positron fraction in cosmic rays was found to be steadily increasing in
function of energy, above $\sim$10 GeV. This behaviour contradicts standard
astrophysical mechanisms, in which positrons are secondary particles, produced
in the interactions of primary cosmic rays during the propagation in the
interstellar medium. The observed anomaly in the positron fraction triggered a
lot of excitement, as it could be interpreted as an indirect signature of the
presence of dark matter species in the Galaxy. Alternatively, it could be
produced by nearby astrophysical sources, such as pulsars. Both hypotheses are
probed in this work in light of the latest AMS-02 positron fraction
measurements. The transport of primary and secondary positrons in the Galaxy is
described using a semi-analytic two-zone model. MicrOMEGAs is used to model the
positron flux generated by dark matter species. We provide mass and
annihilating cross section that best fit AMS-02 data for each single
annihilating channel as well as for combinations of channels. We find that the
mass of the favoured dark matter candidates is always larger than 500 GeV. The
description of the positron fraction from astrophysical sources is based on the
pulsar observations included in the ATNF catalogue. The region of the
distance-to-age plane that best fits the positron fraction for a single source
is determined and a list of five pulsars from the ATNF catalogue is given.
Those results are obtained with the cosmic ray transport parameters that best
fit the B/C ratio. Uncertainties in the propagation parameters turn out to be
very significant.
