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

摘要

The possibility that part of the dark matter is made of massive compact haloobjects (MACHOs) remains poorly constrained over a wide range of masses, andespecially in the $20-100\, M_\odot$ window. We show that strong gravitationallensing of extragalactic fast radio bursts (FRBs) by MACHOs of masses largerthan $\sim20\,M_\odot$ would result in repeated FRBs with an observable timedelay. 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 upcomingexperiments, such as CHIME, of $10^4$ FRBs per year, we should observe fromtens to hundreds of repeated bursts yearly, if MACHOs in this window make upall the dark matter. A null search for echoes with just $10^4$ FRBs, wouldconstrain the fraction $f_{\rm DM}$ of dark matter in MACHOs to $f_{\rmDM}\lesssim 0.08$ for $M_L\gtrsim 20\,M_\odot$.