Lunch talk on Jun. 29, 2023

Pulsar Double-lensing Sheds Light on the Origin of Extreme Scattering Events

Speaker: Hengrui Zhu (Princeton)

Venue: Video Conference

Time: 12:30 PM, Thursday, Jun. 29, 2023

Abstract: 

In extreme scattering events, the brightness of a compact radio source drops significantly, as light is refracted out of the line of sight by foreground plasma lenses. Despite recent efforts, the nature of these lenses has remained a puzzle, because any roughly round lens would be so highly overpressurized relative to the interstellar medium that it could only exist for about a year. This, combined with a lack of constraints on distances and velocities, has led to a plethora of theoretical models. In my talk, I will present observations of a dramatic double-lensing event in pulsar PSR B0834+06 and use a novel phase-retrieval technique to show that the data can be reproduced remarkably well with a two-screen model: one screen with many small lenses and another with a single, strong one. I will further show that the latter lens is so strong that it would inevitably cause extreme scattering events. These observations show that the lens moves slowly and is highly elongated on the sky. If similarly elongated along the line of sight, as would arise naturally from a sheet of plasma viewed nearly edge-on, no large overpressure is required and hence the lens could be long-lived.