A possible wave-optical effect in lensed fast radio bursts

Context. Fast radio bursts (FRBs) are enigmatic extragalactic bursts whose properties are still largely unknown, but based on their extremely short duration, they are proposed to have a compact structure, making them candidates for wave-optical effects if gravitationally lensed. If an FRB is lensed into multiple-image bursts at different times by a galaxy or cluster, a likely scenario is that only one image is detected because the others fall outside the survey area and time frame. Aims. We explore the FRB analog of quasar microlensing, namely the collective microlensing by stars in the lensing galaxy, now including wave optics. The eikonal regime is applicable here. Methods. We studied the voltage (rather than the intensity) in a simple simulation consisting of (a) microlensing stars and (b) plasma scattering by a turbulent interstellar medium. Results. The autocorrelation of the voltage shows peaks (at a separation on the order of microseconds) corresponding to wave-optical interference between lensed micro-images. The peaks are frequency dependent when plasma-scattering is significant. While qualitative and still in need of more realistic simulations, the results suggest that a strongly lensed FRB might be identified from a single image. Conclusions. Macro-lensed FRBs might be recognizable from a microlensing signature.