On the detection of free-floating planets through microlensing towards
  the Magellanic Clouds
  In this work, we study detecting free-floating planets (FFPs) by microlensing
observations towards the Magellanic Clouds (MCs). In comparison to similar
events toward the Galactic bulge, an FFP in the Galactic halo produces on
average longer microlensing events with smaller projected source radii toward
these clouds. For these microlensing events, the relative lens-source
velocities are on average smaller. The MC self-lensing events due to FFPs
suffer from severe finite-source effects. We first simulate microlensing events
due to FFPs towards MCs and assume a log-uniform step function for their mass.
The efficiencies for capturing their lensing signatures (with signal-to-noise
greater than $50$) are found to be $0.1$-$0.6\%$ and $3$-$6\%$ through
ground-based optical surveys and space-based near-infrared surveys,
respectively. We then promote these simulations and assume the
\wfirst~telescope continuously observes each MC during one $72$-day season with
the $15$min observing cadence. From simulated microlensing events with the
resolvable source stars at the baseline due to FFPs with the masses $\sim
0.01$-$10^{4}M_{\oplus}$, \wfirst~discovers their lensing effects with the
efficiencies $\sim 10$-$80\%$, respectively. By adopting $5\%$ as halos
fraction from FFPs we estimate the expected number of events. The highest
number of detectable FFPs which is $\sim1700$-$2200$ per season per square
degree happens for ones with masses $\sim 0.01 M_{\oplus}$. Our simulations
show that \wfirst~potentially extends the mass range of detectable FFPs in
halos down to $5.9\times 10^{-7} M_{\oplus}$ with continuous observations
during one observing season from the Large Magellanic Cloud.
