Real-time detection of an extreme scattering event: constraints on Galactic plasma lenses

TL;DR

This paper presents a new survey method that detected an extreme scattering event in real-time, providing insights into Galactic plasma lenses and challenging existing models of interstellar medium conditions.

Contribution

The study introduces a novel real-time detection technique for ESEs, enabling immediate follow-up and constraining the physical nature of plasma lenses in the Galaxy.

Findings

The detected lens is a diverging density enhancement.

The new technique allows for real-time ESE detection.

Modeling rules out one of the competing physical models.

Abstract

Extreme scattering events (ESEs) are distinctive fluctuations in the brightness of astronomical radio sources caused by occulting plasma lenses in the interstellar medium. The inferred plasma pressures of the lenses are $\sim 10^3$ times the ambient pressure, challenging our understanding of gas conditions in the Milky Way. Using a new survey technique, we have discovered an ESE while it was in progress. We report radio and optical follow-up observations. Modelling of the radio data demonstrates that the lensing structure is a density enhancement and that the lens is diverging, ruling out one of two competing physical models. Our technique will uncover many more ESEs, addressing a long-standing mystery of the small-scale gas structure of the Galaxy.