Pulsar Observations of Extreme Scattering Events

Understand

Extreme scattering events (ESEs) in the interstellar medium (ISM) were first observed in regular flux measurements of compact extragalactic sources.

• They are characterized by a flux variation over a period of weeks, suggesting the passage of a "diverging plasma lens" across the line of sight.
• Modeling the refraction of such a lens indicates that the structure size must be of order AU and the electron density of order 10s of cm^{-3}.
• Similar structures have been observed in measurements of pulsar intensity scintillation and group delay.