Probing isolated compact remnants with microlensing
  We consider isolated compact remnants (ICoRs), i.e. neutrons stars and black
holes that do not reside in binary systems and therefore cannot be detected as
X-ray binaries. ICoRs may represent $\sim\,5$ percent of the stellar mass
budget of the Galaxy, but they are very hard to detect. Here we explore the
possibility of using microlensing to identify ICoRs. In a previous paper we
described a simulation of neutron star evolution in phase space in the Galaxy,
taking into account the distribution of the progenitors and the kick at
formation. Here we first reconsider the evolution and distribution of neutron
stars and black holes adding a bulge component. From the new distributions we
calculate the microlensing optical depth, event rate and distribution of event
time scales, comparing and contrasting the case of ICoRs and "normal stars". We
find that the contribution of remnants to optical depth is slightly lower than
without kinematics, owing to the evaporation from the Galaxy. On the other
hand, the relative contribution to the rate of events is a factor $\sim\,5$
higher. In all, $\sim\,6-7$ percent of the events are likely related to ICoRs.
In particular, $\sim\,30-40$ percent of the events with duration $>\,100$ days
are possibly related to black holes. It seems therefore that microlensing
observations are a suitable tool to probe the population of Galactic ICoRs.
