Lensing of Fast Radio Bursts by Binaries to Probe Compact Dark Matter

TL;DR

This paper explores how gravitational lensing of fast radio bursts by MACHO binaries can be used to detect or constrain the presence of compact dark matter objects in the 20-100 solar mass range.

Contribution

It proposes a novel method to detect or limit the fraction of dark matter in MACHOs using multi-peak FRB observations caused by binary lensing.

Findings

Expected detection of about five multi-peak FRBs per year if MACHOs constitute 1% of dark matter.

Null results from 10,000 FRBs could constrain MACHO dark matter fraction to less than 0.1%.

Lensing signatures include multiple images with millisecond time delays and flux ratios from 10 to 1000.

Abstract

The possibility that a fraction of the dark matter is comprised of massive compact halo objects (MACHOs) remains unclear, especially in the 20-100 $M_{\odot}$ window. MACHOs could make up binaries, whose mergers may be detected by LIGO as gravitational wave events. On the other hand, the cosmological origin of fast radio burst (FRBs) has been confirmed. We investigate the possibility of detecting fast radio bursts (FRBs) gravitational lensed by MACHO binaries to constrain their properties. Since lensing events could generate more than one images, lensing by binaries could cause multiple-peak FRBs. The angular separation between these images is roughly $10^{-3}$ mas, which is too small to be resolved. The typical time interval between different images is roughly 1 millisecond (ms). The flux ratio between different images is roughly from 10 to $10^3$. With the expected detection rate of $10^4$ FRBs per year by the upcoming experiments, we could expect five multi-peak FRBs observed per year with time interval larger than 1 ms and flux ratio less than $10^3$ if the fraction of dark matter in MACHOs is $f\sim0.01$. A null search multiple-peak FRBs for time interval larger than 1 ms and flux ratio less than $10^3$ with $10^4$ FRBs would constrain the fraction $f$ of dark matter in MACHOs to $f<0.001$.