Pulsar
observations with RadioAstron
All radio signals from cosmic sources are distorted by
the plasma turbulence in the interstellar medium (ISM). Understanding
of this turbulence is therefore essential for the proper interpretation
of astronomical radio observations. The properties and characteristics
of this turbulence can best be studied by observing point-like radio
sources, where the results are not infuenced by the extended structure
of the source, but instead are directly attributable to the effect of
the ISM itself. Pulsars are such sources. Dispersion and scattering
affect radio emission from pulsars. Whereas dispersion in the plasma
column introduces delays in arrival time that depend upon frequency and
results in smearing of the pulse, scattering by density inhomogeneities
causes angular broadening, pulse broadening, intensity modulation or
scintillation, and distortion of radio spectra in the form of
dffraction patterns.
The space VLBI mission RadioAstron offers the unique possibility to
observe pulsars at low frequencies and on baselines with projected
lenghts of up to 350,000 km. On such long baselines the scattering disk
of the pulsar is completely resolved and scattering properties of the
interstellar medium can be investigated in detail. We are publishing a
series of papers on pulsars observed with RadioAstron. The Figure below
shows the visibility magnitudes as a function of delay for five
different baselines with their lengths
given in parentheses in units of 1,000 km. The three lower plots show
the signal from the scattering disk at zero delay, stron on the short
ground-ground baseline and weaker on the ground-space baselines. The
two upper plots show that the scattering disk is completely resolved.
Only a distribution of visibility magnitudes along delay remains. This
distribution gives the unique information on the scattering parameters.
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