Stellar prospects for FRB gravitational lensing

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 time-scales from microseconds to years, corresponding to lens masses spanning 15 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 time-scales. 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.

Automated summary

The detection rates and optimal methods for finding gravitational lensing of fast radio bursts (FRBs) are still uncertain. We forecast detection rates of gravitational lensing on timescales ranging from microseconds to years, considering different lens masses and the redshift distribution of FRBs. We discuss the dominant role of strong stellar lensing on microsecond timescales and the potential for detecting millilensing events from intermediate mass black holes or small dark matter halos. We also propose a new application of FRB gravitational lensing to directly measure the circumgalactic medium of intervening galaxies.