Difference imaging photometry of blended gravitational microlensing events with a numerical kernel

TL;DR

This paper introduces a numerical kernel method for difference imaging photometry in blended gravitational microlensing events, improving coordinate determination and flux measurement accuracy.

Contribution

It presents a new algorithm for precise source-star coordinate determination and flux measurement, enhancing the accuracy of difference imaging photometry in microlensing.

Findings

The new algorithm outperforms ISIS2 in accuracy.

Precise source coordinates improve photometry in blended events.

Flux can be derived from difference images without direct reference image measurement.

Abstract

The numerical kernel approach to difference imaging has been implemented and applied to gravitational microlensing events observed by the PLANET collaboration. The effect of an error in the source-star coordinates is explored and a new algorithm is presented for determining the precise coordinates of the microlens in blended events, essential for accurate photometry of difference images. It is shown how the photometric reference flux need not be measured directly from the reference image but can be obtained from measurements of the difference images combined with knowledge of the statistical flux uncertainties. The improved performance of the new algorithm, relative to ISIS2, is demonstrated.