A compact extreme scattering event cloud toward AO 0235+164

Abstract

We present observations of a rare, rapid, high-amplitude extreme scattering event toward the compact BL Lac object AO 0235+164 at 6.65 GHz. The ESE cloud is compact; we estimate its diameter between 0.09 and 0.9 AU, with 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 × 103 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. may be attributed to ESEs.