Kepler K2 Campaign 9: I. Candidate short-duration events from the first
  space-based survey for planetary microlensing
  We present the first short-duration candidate microlensing events from the
Kepler K2 mission. From late April to early July 2016, Campaign 9 of K2
obtained high temporal cadence observations over a 3.7 square degree region of
the Galactic bulge. Its primary objectives were to look for evidence of a
free-floating planet (FFP) population using microlensing, and demonstrate the
feasibility of space-based planetary microlensing surveys. Though Kepler K2 is
far from optimal for microlensing, the recently developed MCPM photometric
pipeline enables us to identify and model microlensing events. We describe our
blind event-selection pipeline in detail and use it to recover 22
short-duration events with effective timescales of less than 10 days previously
announced by the OGLE and KMTNet ground-based surveys. We also announce five
new candidate events. One of these is a caustic-crossing binary event,
consistent with a bound planet and modelled as such in a companion study. The
other four have very short durations (effective timescales less than 0.1 days)
typical of an Earth-mass FFP population. Whilst Kepler was not designed for
crowded-field photometry, the K2C9 dataset clearly demonstrates the feasibility
of conducting blind space-based microlensing surveys towards the Galactic
bulge.
