OGLE-2017-BLG-1130: The First Binary Gravitational Microlens Detected From Spitzer Only

TL;DR

This paper presents the first binary gravitational microlensing event detected solely by the Spitzer Space Telescope, highlighting the importance of space-based observations for identifying binary signals missed from the ground.

Contribution

It introduces a novel analysis approach by first fitting space-based data to determine lens parameters before using ground data for parallax measurement, revealing complex degeneracies.

Findings

Spitzer detected a binary microlensing event missed by ground observations.

The event demonstrates an eight-fold degeneracy in binary-lens microlensing.

The analysis method can resolve degeneracies in space-based microlensing data.

Abstract

We analyze the binary gravitational microlensing event OGLE-2017-BLG-1130 (mass ratio q~0.45), the first published case in which the binary anomaly was only detected by the Spitzer Space Telescope. This event provides strong evidence that some binary signals can be missed by observations from the ground alone but detected by Spitzer. We therefore invert the normal procedure, first finding the lens parameters by fitting the space-based data and then measuring the microlensing parallax using ground-based observations. We also show that the normal four-fold space-based degeneracy in the single-lens case can become a weak eight-fold degeneracy in binary-lens events. Although this degeneracy is resolved in event OGLE-2017-BLG-1130, it might persist in other events.