We report the characterization of a massive (mp = 3:91:4Mjup) microlensing planet (OGLE- 2015-BLG-0954Lb) orbiting an M dwarf host (M = 0:33  0:12M) at a distance toward the Galactic bulge of 0:6+0:4 􀀀0:2 kpc, which is extremely nearby by microlensing standards. The planet-host projected separation is a?  1:2AU. The characterization was made possible by the wide-eld (4 deg2) high cadence (􀀀 = 6 hr􀀀1) monitoring of the Korea Microlensing Telescope Network (KMTNet), which had two of its three telescopes in commissioning operations at the time of the planetary anomaly. The source crossing time t = 16 min is among the shortest ever published. The high-cadence, wide-eld observations that are the hallmark of KMTNet are the only way to routinely capture such short crossings. High-cadence resolution of short caustic crossings will preferentially lead to mass and distance measurements for the lens. This is because the short crossing time typically implies a nearby lens, which enables the measurement of additional eects (bright lens and/or microlens parallax). When combined with the measured crossing time, these eects can yield planet/host masses and distance.

Abstract
1. INTRODUCTION
2. KMTNET
3. OGLE-2015-BLG-0954’S UNFORESEENCAUSTIC CROSSING
4. OBSERVATIONS
5. LIGHT CURVE MODEL
6. COLOR-MAGNITUDE DIAGRAM
7. THE NATURE OF THE LENS
    7.1. A Nearby Lens
    7.2. Lens Properties
8. WHAT IS THE NATURE OF THE BLENDED LIGHT?
    8.1. Astrometry
    8.2. Four Possible Origins of Blended Light
    8.3. Resolution
9. CONCLUSION
REFERENCES

• I.-G. Shin(Harvard-Smithsonian Center for Astrophysics)
• Y.-H. Ryu(Korea Astronomy and Space Science Institute)
• A. Udalski(Warsaw University Observatory)
• M. Albrow(Department of Physics and Astronomy, University of Canterbury)
• S.-M. Cha(Korea Astronomy and Space Science Institute/School of Space Research, Kyung Hee University)
• J.-Y. Choi(Busan National Science Museum)
• S.-J. Chung(Korea Astronomy and Space Science Institute)
• C. Han(Department of Physics, Chungbuk National University)
• K.-H. Hwang(Department of Physics, Chungbuk National University)
• Y. K. Jung(Harvard-Smithsonian Center for Astrophysics)
• D.-J. Kim(Korea Astronomy and Space Science Institute)
• S.-L. Kim(Korea Astronomy and Space Science Institute/Korea University of Science and Technology)
• C.-U. Lee(Korea Astronomy and Space Science Institute/Korea University of Science and Technology)
• Y. Lee(Korea Astronomy and Space Science Institute/School of Space Research, Kyung Hee University)
• B.-G. Park(Korea Astronomy and Space Science Institute/Korea University of Science and Technology)
• H. Park(Busan National Science Museum)
• R. W. Pogge(Department of Astronomy Ohio State University)
• J. C. Yee(Harvard-Smithsonian Center for Astrophysics/Sagan Fellow)
• P. Pietrukowicz(Warsaw University Observatory)
• P. Mroz(Warsaw University Observatory)
• S. Koz lowski(Warsaw University Observatory)
• R. Poleski(Warsaw University Observatory/Department of Astronomy Ohio State University)
• J. Skowron(Warsaw University Observatory)
• I. Soszynski(Warsaw University Observatory)
• M. K. Szymanski(Warsaw University Observatory)
• K. Ulaczyk(Warsaw University Observatory)
• L. Wyrzykowski(Warsaw University Observatory)
• M. Pawlak(Warsaw University Observatory)
• A. Gould(Korea Astronomy and Space Science Institute/Department of Astronomy Ohio State University/Max-Planck-Institute for Astronomy) Corresponding author