Diffractive Microlensing II: Substellar Disk and Halo Objects
  Microlensing is generally studied in the geometric optics limit. However,
diffraction may be important when nearby substellar objects lens occult distant
stars. In particular the effects of diffraction become more important as the
wavelength of the observation increases. Typically if the wavelength of the
observation is comparable to the Schwarzschild radius of lensing object,
diffraction leaves an observable imprint on the lensing signature. The
commissioning of the Square Kilometre Array (SKA) over the next decade begs the
question of whether it will become possible to follow up lensing events with
radio observations because the SKA may have sufficient sensitivity to detect
the typical sources, giant stars in the bulge. The detection of diffractive
lensing in a lensing event would place unique constraints on the mass of the
lens and its distance. In particular it would distinguish rapidly moving
stellar mass lenses (e.g. neutron stars) from slowly moving substellar objects
such freely floating planets. An analysis of the sensitivity of the SKA along
with new simple closed-form estimates of the expected signal applied to local
exemplars for stellar radio emission reveals that this effect can nearly be
detected with the SKA. If the radio emission from bulge giants is stronger than
expected, the SKA could detect the diffractive microlensing signature from
Earth-like interstellar planets in the solar neighborhood.
