MOA-2010-BLG-311: A planetary candidate below the threshold of reliable detection

TL;DR

This study analyzes a high-magnification microlensing event to evaluate the evidence for a planetary companion, highlighting the challenges in reliably detecting planets due to data systematics.

Contribution

It demonstrates that even with a candidate planetary signal, data systematics can prevent a secure detection, informing the threshold for reliable planet identification.

Findings

The event favors a planetary model with a low mass ratio.

Data systematics can obscure genuine planetary signals.

The study helps define the detection threshold in high-magnification microlensing events.

Abstract

We analyze MOA-2010-BLG-311, a high magnification (A_max>600) microlensing event with complete data coverage over the peak, making it very sensitive to planetary signals. We fit this event with both a point lens and a 2-body lens model and find that the 2-body lens model is a better fit but with only Delta chi^2~80. The preferred mass ratio between the lens star and its companion is $q=10^(-3.7+/-0.1), placing the candidate companion in the planetary regime. Despite the formal significance of the planet, we show that because of systematics in the data the evidence for a planetary companion to the lens is too tenuous to claim a secure detection. When combined with analyses of other high-magnification events, this event helps empirically define the threshold for reliable planet detection in high-magnification events, which remains an open question.