Stellar prospects for FRB gravitational lensing

TL;DR

This paper forecasts the detection rates of gravitational lensing in fast radio bursts across various timescales and lens masses, highlighting potential for cosmological insights and dark matter constraints.

Contribution

It provides the first comprehensive forecast of FRB lensing detection rates across a wide range of lens masses and timescales, considering survey capabilities and redshift distributions.

Findings

Strong stellar lensing dominates microsecond timescale events.

Upcoming surveys will constrain dark matter in compact objects.

Longer lensing events from massive galaxies are detectable with all-sky monitors.

Abstract

Gravitational lensing of fast radio bursts (FRBs) offers an exciting avenue for several cosmological applications. However, it is not yet clear how many such events future surveys will detect nor how to optimally find them. We use the known properties of FRBs to forecast detection rates of gravitational lensing on delay timescales from microseconds to years, corresponding to lens masses spanning fifteen orders of magnitude. We highlight the role of the FRB redshift distribution on our ability to observe gravitational lensing. We consider cosmological lensing of FRBs by stars in foreground galaxies and show that strong stellar lensing will dominate on microsecond timescales. Upcoming surveys such as DSA-2000 and CHORD will constrain the fraction of dark matter in compact objects (e.g. primordial black holes) and may detect millilensing events from intermediate mass black holes (IMBHs) or small dark matter halos. Coherent all-sky monitors will be able to detect longer-duration lensing events from massive galaxies, in addition to short time-scale lensing. Finally, we propose a new application of FRB gravitational lensing that will measure directly the circumgalactic medium of intervening galaxies.