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Session 46 - Interstellar Scattering and Scintillation as Tools in Radio Astronomy.
Topical, Oral session, Tuesday, June 09
Sierra/Padre,
The nearby pulsar B0809+74 should be in the regime of weak
interstellar scintillation at all frequencies above about 1
GHz, based on extrapolating 400 MHz observations using a
Kolmogorov spectral model. The predicted time scale at 933
MHz is about 1 hr. The source is circumpolar at the
EISCAT-Sodankyla site in Finland, and we were able to take
advantage of a receiver test to observe it continuously at
933 MHz for 80 hours. The observations showed that the
source was on the edge of weak scintillation with a
scintillation index S_rms/ = 0.90, and a time
scale of 1.9 hr.
The 80 hr observation was long enough to provide a reliable estimate of the intensity structure function, which we have compared with a weak scintillation theoretical model. The model includes the distribution of interstellar plasma turbulence along the line-of-sight; its spectral exponent; and the velocities of the pulsar, the observer and the turbulent plasma. The observations are consistent with a Kolmogorov spectrum and various distributions of turbulence along the line-of-sight, including a thin screen. In this paper we will show the range of models which provide an adequate match to the observations, including the model proposed by Bhat et al. (submitted to MNRAS 1998) in which there is enhanced scattering at the edge of the local super-bubble.
