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[36.04] Scintillation as the cause of Intraday Variability at cm Wavelengths

B.J. Rickett (U.C. San Diego)

Rapid (intraday) flux density variations observed at cm wavelengths are more readily explained as scintillation in the ionized interstellar medium than by intrinsic models. Whereas the latter yield brightness temperatures many orders of magnitude above those found from VLBI, temperatures found from scintillation models are consistent with the canonical jet models with Doppler factors similar to those found from VLBI.

I will review the many lines of evidence in support of scintillation, concentrating on results from the most rapid variables, which are scattered in unusually nearby regions of the interstellar medium. I will also show preliminary results from a recent survey of 700 flat spectrum sources in which more than 12% vary on times shorter than two days, suggesting brightness temperatures no more than about 10¹² K.

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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.