Ogle-2009-BLG-092/Moa-2009-BLG-137: A Dramatic Repeating Event With the Second Perturbation Predicted by Real-Time Analysis

Abstract

We report the result of the analysis of a dramatic repeating gravitational microlensing event OGLE-2009-BLG-092/MOA-2009, for which the light curve is characterized by two distinct peaks with perturbations near both peaks. We find that the event is produced by the passage of the source trajectory over the central perturbation regions associated with the individual components of a wide-separation binary. The event is special in the sense that the second perturbation, occurring ∼100 days after the first, was predicted by the real-time analysis conducted after the first peak, demonstrating that real-time modeling can be routinely done for binary and planetary events. With the data obtained from follow-up observations covering the second peak, we are able to uniquely determine the physical parameters of the lens system. We find that the event occurred on a bulge clump giant and it was produced by a binary lens composed of a K-and M-type main-sequence stars. The estimated masses of the binary components are M 1 = 0.69±0.11 M and M 2 = 0.36±0.06 M , respectively, and they are separated in projection by r ⊥ = 10.9±1.3 AU. The measured distance to the lens is D L = 5.6 ± 0.7 kpc. We also detect the orbital motion of the lens system.

Three-dimensional microlensing

“…In a single plane Galactic microlensing, the motion of the centre of the mass of the binary can be absorbed into the motion of the source, although the binary rotation (of the order of ∼ 10 km s −1 ) can still be observed (Albrow et al 2000;An et al 2002;Jaroszynski et al 2005;Hwang et al 2010;Ryu et al 2010; for predictions see, . For three-dimensional lensing, the two lenses will move independently with velocities of 100 km s −1 , and so the distance between the lenses, and as a result critical curves and caustics, will change as a function of time more rapidly, which may further diversify the light curves.…”

Microlensing Searches for Exoplanets

“…As the event progresses and more observations are obtained, the likelihood of the different interpretations changes, but estimating exactly by how much requires the ability to model events in real-time as they are happening, and to constantly re-evaluate how well these models represent the data. This was computationally prohibitively expensive until 2010 when, based on previous work in the field, Bozza [135] came up with a conceptually simple method that could evaluate competing models in-real time and help follow-up teams decide whether to continue intensive observations or to reallocate their resources to a different target [136,137]. Furthermore, the software product was made publicly available and could be run on an average laptop.…”

The OGLE-III planet detection efficiency from six years of microlensing observations (2003–2008)

“…A small subset of these events are selected for monitoring by follow-up teams (RoboNet 4 , PLANET 5 , MiND-STeP 6 , µFUN 7 ) to look for planetary deviations. Anomalies are generally recognized in real time and secondary alerts are issued (Ryu et al 2010) to trigger higher cadence observations that can confirm or disprove the planetary nature of the event. All teams pool their resources and observe the anomalous features from multiple telescopes in order to fully characterize the potential planet.…”