We present the analysis of four candidate short duration binary microlensing events from the 2006-2007 MOA Project short event analysis .
These events were discovered as a byproduct of an analysis designed to find short timescale single lens events that may be due to free-floating planets .
Three of these events are determined to be microlensing events , while the fourth is most likely caused by stellar variability .
For each of the three microlensing events , the signal is almost entirely due to a brief caustic feature with little or no lensing attributable mainly to the lens primary .
One of these events , MOA-bin-1 , is due to a planet , and it is the first example of a planetary event in which stellar host is only detected through binary microlensing effects .
The mass ratio and separation are q = 4.9 \pm 1.4 \times 10 ^ { -3 } and s = 2.10 \pm 0.05 , respectively .
A Bayesian analysis based on a standard Galactic model indicates that the planet , MOA-bin-1Lb , has a mass of m _ { p } = 3.7 \pm 2.1 M _ { Jup } , and orbits a star of M _ { \ast } = 0.75 { +0.33 \atop - 0.41 } M _ { \odot } at a semi-major axis of a = 8.3 { +4.5 \atop - 2.7 } AU .
This is one of the most massive and widest separation planets found by microlensing .
The scarcity of such wide separation planets also has implications for interpretation of the isolated planetary mass objects found by this analysis .
If we assume that we have been able to detect wide separation planets with a efficiency at least as high as that for isolated planets , then we can set limits on the distribution on planets in wide orbits .
In particular , if the entire isolated planet sample found by Sumi et al .
( 71 ) consists of planets bound in wide orbits around stars , we find that it is likely that the median orbital semi-major axis is > 30 AU .