Diffractive Microlensing III: Astrometric Signatures

TL;DR

This paper explores the astrometric effects of diffractive microlensing, deriving new signatures and bounds relevant for high-resolution radio observations of substellar objects.

Contribution

It introduces the first derivation of astrometric signatures of diffractive microlensing and provides a simple bound for maximal astrometric shifts.

Findings

Derived the first astrometric signatures of diffractive microlensing.

Provided a simple bound for maximal astrometric shifts.

Showed relevance for high-frequency radio telescopes like SKA.

Abstract

Gravitational lensing is generally treated in the geometric optics limit; however, when the wavelength of the radiation approaches or exceeds the Schwarzschild radius of the lens, diffraction becomes important. Although the magnification generated by diffractive gravitational lensing is well understood, the astrometric signatures of diffractive microlensing are first derived in this paper along with a simple closed-form bound for the astrometric shift. This simple bound yields the maximal shifts for substellar lenses in solar neighbourhood observed at 20~GHz, accessible to high sensitivity, high angular resolution radio telescopes such as the proposed Square Kilometre Array (SKA).