Microlensing Zone of Planets Detectable through the Channel of High-Magnification Events

Abstract

A microlensing lensing zone refers to the range of planet-star separations where the probability of detecting a planetary signal is high. Its conventional definition as the range between $\sim 0.6$ and 1.6 Einstein radii of the primary lens is based on the criterion that a major caustic induced by a planet should be located within the Einstein ring of the primary. However, current planetary lensing searches focus on high-magnification events to detect perturbations induced by another caustic located always within the Einstein ring very close to the primary lens (stellar caustic) and thus a new definition of a lensing zone is needed. In this paper, we determine this lensing zone. By applying a criterion that detectable planets should produce signals $\ge 5$, we find that the new lensing zone varies depending on the planet/star mass ratio unlike the fixed range of the classical zone regardless of the mass ratio. The lensing zone is equivalent to the classical zone for a planet with a planet/star mass ratio $q\sim 3\times 10^{-4}$ and it becomes wider for heavier planets. For a Jupiter-mass planet, the lensing zone ranges from 0.25 to 3.9 Einstein radii, corresponding to a physical range between $\sim 0.5$ AU and 7.4 AU for a typical Galactic event. The wider lensing zone of central perturbations for giant planets implies that the microlensing method provides an important tool to detect planetary systems composed of multiple ice-giant planets.

6 pages, 5 figures

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• Distinguishing between Planetary and Binary Interpretations of Microlensing Central Perturbations under Severe Finite-Source Effect
• Microlensing by a wide-separation planet: detectability and boundness
• Extending the Planetary Mass Function to Earth Mass by Microlensing at Moderately High Magnification
• Planetary Lensing Signals of High-Magnification Events under Severe Finite-Source Effect
• KMT-2018-BLG-1025Lb: microlensing super-Earth planet orbiting a low-mass star
• Investigating the free-floating planet mass by Euclid observations
• Interpretation of Strong Short-Term Central Perturbations in the Light Curves of Moderate-Magnification Microlensing Events