Subaru-HSC through a different lens: Microlensing by extended dark matter structures

We investigate gravitational microlensing signals produced by a spatially extended object transiting in front of a finite-sized source star. The most interesting features arise for lens and source sizes comparable to the Einstein radius of the setup. Using this information, we obtain constraints from the Subaru-HSC survey of M31 on the dark matter populations of NFW subhalos and boson stars of asteroid to Earth masses. These lens profiles capture the qualitative behavior of a wide range of dark matter substructures. We find that dark matter fractions down to 5 x 10(-3) may be probed, and that deviations from constraints on pointlike lenses (e.g., primordial black holes and MACHOs) become visible for lenses of radius 0.1 R. and larger, with the upper bound on lens masses weakening with increasing lens size.