Gravitational microlensing as a probe for dark matter clumps

TL;DR

This paper investigates how gravitational microlensing can be used to detect and differentiate dark matter substructures, including extended clumps, by analyzing their effects on light curves and autocorrelation functions.

Contribution

It introduces a simple model comparing microlensing effects of point masses and extended dark matter clumps, and explores their distinguishability in observational data.

Findings

High amplification events can constrain dark matter clump parameters.

Clump size significantly affects autocorrelation functions of microlensing light curves.

Distinguishing between point lenses and extended clumps is challenging but possible with precise data.

Abstract

Extended dark matter (DM) substructures may play the role of microlenses in the Milky Way and in extragalactic gravitational lens systems (GLSs). We compare microlensing effects caused by point masses (Schwarzschild lenses) and extended clumps of matter using a simple model for the lens mapping. A superposition of the point mass and the extended clump is also considered. For special choices of the parameters, this model may represent a cusped clump of cold DM, a cored clump of self-interacting dark matter (SIDM) or an ultra compact minihalo of DM surrounding a massive point-like object. We built the resulting micro-amplification curves for various parameters of one clump moving with respect to the source in order to estimate differences between the light curves caused by clumps and by point lenses. The results show that it may be difficult to distinguish between these models. However, some region of the clump parameters can be restricted by considering the high amplification events at the present level of photometric accuracy. Then we estimate the statistical properties of the amplification curves in extragalactic GLSs. For this purpose, an ensemble of amplification curves is generated yielding the autocorrelation functions (ACFs) of the curves for different choices of the system parameters. We find that there can be a significant difference between these ACFs if the clump size is comparable with typical Einstein radii; as a rule, the contribution of clumps makes the ACFs less steep.