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Session 46 - Interstellar Scattering and Scintillation as Tools in Radio Astronomy.
Topical, Oral session, Tuesday, June 09
In recent years Interstellar Scintillation (ISS) has been identified as causing variations in flux density in a variety of radio astronomical observations. Although this ``Galactic seeing'' effect is in some ways a nuisance, ISS is also a valuable tool that provides information on radio source structure at angular scales well beyond the reach of all current interferometers. In addition to ISS, angular and temporal broadening have been measured on many lines of sight in the Galaxy. Such measurements also provide a probe for the fine scale structure in the ionized interstellar plasma.
The session will explore the science that can be done using these tools to probe both very compact radio sources and the interstellar plasma. Examples include:
\beginitemize \item ISS provides an explanation of rapid (hours to days - intraday) flux variations at centimeter wavelengths from compact cores of AGNs, reducing the implied brightness temperature by up to six orders of magnitude.
\item ISS has beeen recognised as causing the flux variations from the radio afterglow of the gamma-ray burst observed on May 8 1997, from which a diameter of a few microarcseconds has been estimated for the expanding fireball.
\item A study of the interstellar speckle pattern of the Vela pulsar has achieved nanoarcsecond angular resolution of the pulsar magnetosphere.
\item The Galaxy is permeated by irregular density structures, whose wavenumber spectrum is like a turbulent fluid over at least six and as many as ten orders of magnitude in length scale. However, the local strength of turbulence is itself non-uniform, with localized enhancemnents by more than six orders of magnitude, whose physical origin is still obscure.
Program listing for Tuesday