Pulsar emission amplified and resolved by plasma lensing in an eclipsing binary

TL;DR

This paper reports extreme plasma lensing events in the Black Widow pulsar, resolving emission regions and providing insights into plasma lensing effects, with implications for understanding fast radio bursts like FRB 121102.

Contribution

It demonstrates that plasma lensing near the pulsar can resolve emission regions at ~10 km scale, offering new observational evidence and linking to fast radio burst phenomena.

Findings

Flux enhancement up to 80 times at specific frequencies.

Resolved emission regions affecting main pulse and interpulse differently.

Lenses inferred to have resolution comparable to pulsar radius (~10 km).

Abstract

Radio pulsars scintillate because their emission travels through the ionized interstellar medium via multiple paths, which interfere with each other. It has long been realized that the scattering screens responsible for the scintillation could be used as `interstellar lenses' to localize pulsar emission regions. Most scattering screens, however, only marginally resolve emission components, limiting results to statistical inferences and detections of small positional shifts. Since screens situated close to the source have better resolution, it should be easier to resolve emission regions of pulsars located in high density environments such as supernova remnants or binaries in which the pulsar's companion has an ionized outflow. Here, we report events of extreme plasma lensing in the `Black Widow' pulsar, PSR~B1957+20, near the phase in its 9.2 hour orbit in which its emission is eclipsed by its companion's outflow. During the lensing events, the flux is enhanced by factors of up to 70--80 at specific frequencies. The strongest events clearly resolve the emission regions: they affect the narrow main pulse and parts of the wider interpulse differently. We show that the events arise naturally from density fluctuations in the outer regions of the outflow, and infer a resolution of our lenses comparable to the pulsar's radius, about 10\,km. Furthermore, the distinct frequency structures imparted by the lensing are reminiscent of what is observed for the repeating fast radio burst FRB 121102, providing observational support for the idea that this source is observed through, and thus at times strongly magnified by, plasma lenses.