Scintillated microlensing: measuring cosmic distances with fast radio bursts

TL;DR

This paper introduces a new method to measure cosmic distances using scintillated microlensing of fast radio bursts, which could provide precise estimates of the Hubble constant by overcoming systematic uncertainties in traditional methods.

Contribution

The paper proposes using scintillation in the interstellar medium to resolve microlensed images of FRBs, enabling direct and precise measurement of the Hubble constant with minimal systematic errors.

Findings

Estimated 6% uncertainty on H0 from a single event

Sub-percent uncertainty on H0 possible with 30 events

Method feasible with upcoming FRB telescopes

Abstract

We propose a novel means of directly measuring cosmological distances using scintillated microlensing of fast radio bursts (FRBs). In standard strong lensing measurements of cosmic expansion, the main source of systematic uncertainty lies in modeling the mass profile of galactic halos. Using extra-galactic stellar microlensing to measure the Hubble constant avoids this systematic uncertainty as the lens potential of microlenses depends only on a single parameter: the mass of the lens. FRBs, which may achieve nanosecond precision on lensing time delays, are well-suited to precision measurements of stellar microlensing, for which the time delays are on the order of milliseconds. However, typical angular separations between the microlensed images on the order of microarcseconds make the individual images impossible to spatially resolve with ground-based telescopes. We propose leveraging scintillation in the ISM to resolve the microlensed images, effectively turning the ISM into an astrophysical-scale interferometer. Using this technique, we estimate a 6\% uncertainty on $H_0$ from a single observed scintillated microlensing event, with a sub-percent uncertainty on $H_0$ achievable with only 30 such events. With an optical depth for stellar microlensing of $10^{-3}$, this may be achievable in the near future with upcoming FRB telescopes.