Interpretation of Extreme Scattering Events

Abstract

Extreme Scattering Events are sometimes manifest in the light-curves of compact radio-quasars at frequencies of a few GHz. These events are not understood. The model which appears to offer the best explanation requires a new population of AU-sized, neutral gas clouds; these clouds would then make up a large fraction of the Galaxy's dark matter. Independent of the question of which theoretical model is correct, if we extrapolate the observed behaviour to low radio-frequencies, we expect that the sky should be criss-crossed by a network of narrow caustics, at frequencies below about 700 MHz. Consequently at these frequencies sources should typically manifest additional, faint images which are substantially delayed with respect to the primary image. Although some examples of this type of behaviour are already known, it is expected that these are just the tip of the iceberg, with strong selection biases having been imposed by the instrumentation employed to date.

6 pages, 1 figure; to appear in Proc. IAU Coll. 182 ``Sources and Scintillations: refraction and scattering in radio astronomy'' (Special edition of ApSS)

References in corpus (2)

• Extreme scattering events and Galactic dark matter
• The Cloudy Universe

Cited by in corpus (7)

• Deflection of Pulsar Signal Reveals Compact Structures in the Galaxy
• Pulsar scintillations from corrugated reconnection sheets in the ISM
• Scattering analysis of LOFAR pulsar observations
• First detection of frequency-dependent, time-variable dispersion measures
• Extreme scattering events from axisymmetric plasma lenses
• Pulsar scintillation patterns and strangelets
• High-resolution imaging with the International LOFAR Telescope: Observations of the gravitational lenses MG 0751+2716 and CLASS B1600+434