We have made high-resolution , high-sensitivity dynamic spectra of a sample of strong pulsars at 430 MHz with the Arecibo radiotelescope .
For 4 pulsars we find faint but sharply delineated features in the secondary spectra .
These are examples of the previously observed “ crisscross ” or “ multiple drift slope ” phenomenon presumed to be due to multiple imaging of the pulsar by the interstellar medium .
The unprecedented resolution and dynamic range of our observations allow a deeper level of analysis .
Distances to the dominant scattering screen along the line of sight are determined and are shown to agree well with those inferred from other scintillation phenomena .
Multiple imaging of the pulsar by the ISM is required .
A compact central image surrounded by a faint scattering halo , roughly circularly symmetric , is consistent with the data .
Scattering from filaments may also be consistent .
The angular extent of the scattering material parallel to the direction of the pulsar velocity is \sim 5 mas , corresponding to a linear extent of \sim 2 AU .
Further observations of these features should allow better discrimination between models and an identification of the scattering structures .