Probing planetary mass dark matter in galaxies: gravitational
  nanolensing of multiply imaged quasars
  Gravitational microlensing of planetary-mass objects (or "nanolensing", as it
has been termed) can be used to probe the distribution of mass in a galaxy that
is acting as a gravitational lens. Microlensing and nanolensing light curve
fluctuations are indicative of the mass of the compact objects within the lens,
but the size of the source is important, as large sources will smooth out a
light curve. Numerical studies have been made in the past that investigate a
range of sources sizes and masses in the lens. We extend that work in two ways
- by generating high quality maps with over a billion small objects down to a
mass of 2.5\times10-5M\odot, and by investigating the temporal properties and
observability of the nanolensing events. The system studied is a mock quasar
system similar to MG 0414+0534. We find that if variability of 0.1 mag in
amplitude can be observed, a source size of ~ 0.1 Einstein Radius (ER) would be
needed to see the effect of 2.5\times10-5M\odot masses, and larger, in the
microlensing light curve. Our investigation into the temporal properties of
nanolensing events finds that there are two scales of nanolensing that can be
observed - one due to the crossing of nanolensing caustic bands, the other due
to the crossing of nanolensing caustics themselves. The latter are very small,
having crossing times of a few days, and requiring sources of size ~ 0.0001 ER
to resolve. For sources of the size of an accretion disk, the nanolensing
caustics are slightly smoothed-out, but can be observed on time scales of a few
days. The crossing of caustic bands can be observed on times scales of about 3
months.
