Lensing of Fast Radio Bursts as a Probe of Compact Dark Matter

TL;DR

This paper proposes using gravitational lensing of fast radio bursts (FRBs) to detect or constrain the presence of massive compact halo objects (MACHOs) as dark matter, predicting observable repeated signals for certain mass ranges.

Contribution

It introduces a novel method to probe dark matter MACHOs via FRB lensing, providing estimates for detection rates and constraints on dark matter fraction.

Findings

Repeated FRBs could be observed if MACHOs are present in the 20-100 M_sun range.

Upcoming FRB surveys could constrain MACHO dark matter fraction to less than 8%.

Null results would significantly limit the contribution of MACHOs to dark matter.

Abstract

The possibility that part of the dark matter is made of massive compact halo objects (MACHOs) remains poorly constrained over a wide range of masses, and especially in the $20-100\, M_\odot$ window. We show that strong gravitational lensing of extragalactic fast radio bursts (FRBs) by MACHOs of masses larger than $\sim20\,M_\odot$ would result in repeated FRBs with an observable time delay. Strong lensing of an FRB by a lens of mass $M_L$ induces two images, separated by a typical time delay $\sim$ few $\times(M_L/30\, M_\odot)$ milliseconds. Considering the expected FRB detection rate by upcoming experiments, such as CHIME, of $10^4$ FRBs per year, we should observe from tens to hundreds of repeated bursts yearly, if MACHOs in this window make up all the dark matter. A null search for echoes with just $10^4$ FRBs, would constrain the fraction $f_{\rm DM}$ of dark matter in MACHOs to $f_{\rm DM}\lesssim 0.08$ for $M_L\gtrsim 20\,M_\odot$.