A Compact Extreme Scattering Event Cloud Towards AO 0235+164

TL;DR

This paper reports the observation of a rare, rapid Extreme Scattering Event towards the BL-Lac AO 0235+164, providing estimates of the cloud's size, distance, and electron density, and suggesting ESEs may explain some transient radio sources.

Contribution

First detailed measurement and analysis of a rapid ESE cloud towards AO 0235+164, estimating its physical properties and implications for transient radio phenomena.

Findings

ESE cloud diameter between 0.09 and 0.9 AU

Cloud located within 3.6 kpc from Earth

At least one transient may be caused by ESEs

Abstract

We present observations of a rare, rapid, high amplitude Extreme Scattering Event toward the compact BL-Lac AO 0235+164 at 6.65 GHz. The ESE cloud is compact; we estimate its diameter between 0.09 and 0.9 AU, and is at a distance of less than 3.6 kpc. Limits on the angular extent of the ESE cloud imply a minimum cloud electron density of ~ 4 x 10^3 cm^-3. Based on the amplitude and timescale of the ESE observed here, we suggest that at least one of the transients reported by Bower et al. (2007) may be attributed to ESEs.