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

Abstract

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 $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ may be probed, and that deviations from constraints on pointlike lenses (e.g., primordial black holes and machos) become visible for lenses of radius $0.1\text{ }\text{ }{\mathrm{R}}_{\ensuremath{\bigodot}}$ and larger, with the upper bound on lens masses weakening with increasing lens size.